Post by: luken93 on March 16, 2011, 07:48:48 pm
I figure we could all get something out of every question made, but could we please keep it to theory or Why is/does/how etc? questions only as opposed to textbook questions.
Post by: luken93 on March 16, 2011, 07:50:40 pm
Why is Cr2O72- / H+ used as a catalyst for oxidation, and what does it therefore mean having the / H+ on the bottom of the arrow in a reaction?
Post by: Mao on March 16, 2011, 08:56:34 pm
Note that: this is a reduction equation, dichromate is an oxidant, dichromate causes oxidation, thus it is used when an organic compound need to be oxidized/etc. It is not a catalyst, it is required for the reaction.
Also note that this reaction consumes protons, thus only adding dichromate is not enough. You must always have plenty of acid to go with dichromate. You almost never see a dichromate solution, it is always available as 'acidified dichromate' to activate the oxidative reaction.
The use and behaviour of permanganate is very similar.
Post by: luken93 on March 16, 2011, 09:02:47 pm
Post by: meli001 on March 16, 2011, 09:12:33 pm
Post by: luken93 on March 16, 2011, 09:16:59 pm
Post by: Bozo on March 17, 2011, 06:19:43 pm
Post by: nacho on March 17, 2011, 06:34:44 pm
-Just a headsup : This is a back titration. Reacted lawn feed solution with excess NaOH. Remaining NaOH was reacted against HCl.
Q1. The supplied value for [HCl] was lower than its true value.
Q2. The distilled water was found to have a pH of 6.0
Post by: luken93 on March 17, 2011, 07:33:45 pm
Is Ba(H2PO4)2 insoluble?Wouldn't it be an Ionic Compound? (Barium is a metal, Phosphate is a non-metal)
Therefore, it is highly polar as it has a large difference in electronegativities - hence it is soluble...
I'd wait for this to be confirmed though.
Post by: luken93 on March 17, 2011, 07:37:54 pm
Predict the effect of the following on the experimental value for the concentration of nitrogein in the lawn feed: would it cause it to be higher than or lower than the true value, or have no effect? Justify each answer.Supplied value = Concentration?
-Just a headsup : This is a back titration. Reacted lawn feed solution with excess NaOH. Remaining NaOH was reacted against HCl.
Q1. The supplied value for [HCl] was lower than its true value.
Q2. The distilled water was found to have a pH of 6.0
If it is concentration, then more HCl would be required to neutralise the NaOH. As a result, you would think that more NaOH was left in excess after the first reaction, and hence a lower % of Nitrogen would be given in the lawn feed because it would seem less has reacted with it.
Q2, where was the distilled water used?
Post by: nacho on March 17, 2011, 08:23:00 pm
i believe the supplied value is the value we're given on the label (i.e, what we are made to think) and the true value is the real concentration.Predict the effect of the following on the experimental value for the concentration of nitrogein in the lawn feed: would it cause it to be higher than or lower than the true value, or have no effect? Justify each answer.Supplied value = Concentration?
-Just a headsup : This is a back titration. Reacted lawn feed solution with excess NaOH. Remaining NaOH was reacted against HCl.
Q1. The supplied value for [HCl] was lower than its true value.
Q2. The distilled water was found to have a pH of 6.0
If it is concentration, then more HCl would be required to neutralise the NaOH. As a result, you would think that more NaOH was left in excess after the first reaction, and hence a lower % of Nitrogen would be given in the lawn feed because it would seem less has reacted with it.
Q2, where was the distilled water used?
distilled water used for washing the volumetric flask (and any other places u would use distilled water to wash.
thanks
Post by: pi on March 17, 2011, 09:16:28 pm
Is Ba(H2PO4)2 insoluble?
Generally phosphates are insoluble, so I think that one will be too
Post by: Mao on March 17, 2011, 10:19:40 pm
Is Ba(H2PO4)2 insoluble?
Generally phosphates are insoluble, so I think that one will be too
I wouldn't be so sure. Phosphates are generally insoluble. dihydrogenphosphates, not so sure. (I have no idea whether it is soluble or not)
Moderator action: removed real name, sorry for the inconvenience
Post by: annabri on March 19, 2011, 03:01:09 pm
also how do i write a conclusion for an organic prac!?
short and sweet but what should it include?
Post by: pi on March 19, 2011, 03:03:28 pm
Post by: luken93 on April 03, 2011, 06:35:34 pm
Can someone please clarify the Primary, Secondary and Tertiary Structure of DNA/Proteins.
Is it the following:
DNA
Primary = Sequence of nucleotides along a single strand, hence the bond is between the Phosphate/Deoxyribose Sugars
Secondary = The complementary Base Pairing between the two strands, hence the bonding is hydrogen bonding between AT and GC
Tertiary = The ionic bonding that occurs between the negatively charged Phosphate Groups and the positively charged histones, allowing for it to be super-coiled.
Proteins
Primary = The sequence of Amino Acids, bonded together covalently by Peptide Linkages (CO-NH)
*Secondary = The coiling, bending or folds of the chain that are caused by Hydrogen Bonding between carboxyl and amine groups along the chain (bonding isn't on the adjacent amino acid, but one that is pulled close when coiled)
*Tertiary = Affected by the side chains of amino acids, and can be formed/modified by hydrogen bonding (between CO-HN), covalent bonding (between S-S creating a disulfide bridge), and ionic bonding (between NH2 and COOH)
*I don't think these are entirely correct, so any opinions would be appreciated :)
Post by: VivaTequila on April 03, 2011, 06:44:58 pm
wow at below
Post by: TortMequila on April 04, 2011, 09:38:15 am
Post by: luken93 on May 11, 2011, 07:04:33 pm
When a question gives you a mixture and they ask you whether GLC/HPLC would be more appropriate, is there an easy way to knowing this?
I know that HPLC is used for substances that usually have an Mr > 300, and may decompose upon heating.
But if you are presented with say perfume, how do you know which to use?
Is it more logic than anything of what is in it?
Post by: Graphite on May 11, 2011, 07:14:42 pm
Post by: luken93 on May 11, 2011, 07:28:11 pm
Think about which one is used for volatile liquids which perfume is.Yeah, but HOW do you know it is a volatile liquid is more what I'm asking..
Post by: Graphite on May 11, 2011, 07:44:41 pm
Post by: Graphite on May 11, 2011, 07:48:13 pm
Post by: luken93 on May 11, 2011, 08:53:25 pm
It makes sense if the substance is volatile, it would evaporate into your noseThat's actually a really good way of putting it!
However, I assume it's not limited to only substances you can smell?
Post by: jane1234 on May 11, 2011, 10:15:00 pm
No, a volatile substance is any one that readily gives off a gas.It makes sense if the substance is volatile, it would evaporate into your noseThat's actually a really good way of putting it!
However, I assume it's not limited to only substances you can smell?
Post by: Zebra on May 11, 2011, 10:33:13 pm
Obviously there are some straight forward ones but sometimes I struggled with some compounds!
Post by: Graphite on May 12, 2011, 10:46:09 am
I described a property of volatile liquids. They do evaporate more easily based on the weak interactions at the surface of the liquid therefore evaporate => a gaseous phase.No, a volatile substance is any one that readily gives off a gas.It makes sense if the substance is volatile, it would evaporate into your noseThat's actually a really good way of putting it!
However, I assume it's not limited to only substances you can smell?
Post by: jackson1234 on May 12, 2011, 04:21:04 pm
Post by: pi on May 12, 2011, 10:27:43 pm
for writing the states for reactants and products... do we have to remember the solubility rules?
Obviously there are some straight forward ones but sometimes I struggled with some compounds!
Yep, you should know them (and most common exceptions) :(
Post by: luken93 on May 12, 2011, 10:35:20 pm
Has anyone good a decent summary of the "common exceptions"?for writing the states for reactants and products... do we have to remember the solubility rules?
Obviously there are some straight forward ones but sometimes I struggled with some compounds!
Yep, you should know them (and most common exceptions) :(
Would be handy :)
Moderator action: removed real name, sorry for the inconvenience
Post by: Graphite on May 13, 2011, 03:22:16 pm
for writing the states for reactants and products... do we have to remember the solubility rules?Yes, in fact that is the point of understanding them. To predict the state of the product.
Obviously there are some straight forward ones but sometimes I struggled with some compounds!
Post by: pi on May 13, 2011, 05:19:03 pm
Has anyone good a decent summary of the "common exceptions"?for writing the states for reactants and products... do we have to remember the solubility rules?
Obviously there are some straight forward ones but sometimes I struggled with some compounds!
Yep, you should know them (and most common exceptions) :(
Would be handy :)
I copied from here: http://www.ausetute.com.au/solrules.html
Moderator action: removed real name, sorry for the inconvenience
Post by: luken93 on May 13, 2011, 05:32:43 pm
Also, which substances/reactions are liquid rather than aqueous?
This may seem really simple to some, but just want to make sure..
Moderator action: removed real name, sorry for the inconvenience
Post by: luken93 on May 15, 2011, 08:30:56 pm
- Hydroxy vs Hydroxyl - Does it matter?
- Is there a difference between Transesterification and Esterification? Is Trans used for Biodiesel especially?
More will come as I think of them.
Post by: scocliffe09 on May 15, 2011, 09:21:33 pm
More questions. Well, more just safeguard checking :PHydroxy = hydroxyl.
- Hydroxy vs Hydroxyl - Does it matter?
- Is there a difference between Transesterification and Esterification? Is Trans used for Biodiesel especially?
More will come as I think of them.
Esterification = formation of ester, usually by the joining of an OH group with a COOH group condensing to produce water.
Transesterification: alcohol + ester → different alcohol + different ester
Post by: luken93 on May 15, 2011, 09:47:12 pm
Cheers.More questions. Well, more just safeguard checking :PHydroxy = hydroxyl.
- Hydroxy vs Hydroxyl - Does it matter?
- Is there a difference between Transesterification and Esterification? Is Trans used for Biodiesel especially?
More will come as I think of them.
Esterification = formation of ester, usually by the joining of an OH group with a COOH group condensing to produce water.
Transesterification: alcohol + ester → different alcohol + different ester
Post by: luken93 on May 17, 2011, 07:47:28 am
Can you write C2H5OH as opposed to C2H6O? I understand what semi-structural and molecular are, but not sure if it's allowed.
Post by: scocliffe09 on May 17, 2011, 04:06:42 pm
Also, may be a silly question but nonetheless.yep they're both correct I think. When it comes to lipids - just be careful, because they can be written differently on the exam to how they are written in the data book...
Can you write C2H5OH as opposed to C2H6O? I understand what semi-structural and molecular are, but not sure if it's allowed.
Post by: luken93 on May 17, 2011, 04:36:24 pm
Yeah, I wasn't really sure as it's kinda semi-strucural, but it would be harder to recognise a Carboxyl with an Ester if you had to write it in full molecular.Also, may be a silly question but nonetheless.yep they're both correct I think. When it comes to lipids - just be careful, because they can be written differently on the exam to how they are written in the data book...
Can you write C2H5OH as opposed to C2H6O? I understand what semi-structural and molecular are, but not sure if it's allowed.
And by the lipids you just mean combining the Carboxyl into the Molecular Formula, ie C18H37COOH = C19H38O2?
Post by: luken93 on May 22, 2011, 07:21:46 pm
Also, while on indicators, if you had to choose between Phenolphthalein and Methyl Red as an indicator for a strong vs strong reaction, would any of them be better? By this I mean would it be better to look for a colourless -> red or red -> yellow? It probably sounds stupid, but just want to make sure I'm thinking straight :P
Post by: Andiio on May 22, 2011, 09:34:53 pm
I got it right but... I'm paranoid that my reasoning is dodgy >_>
Thanks!
Post by: luken93 on May 22, 2011, 10:00:37 pm
I know what you mean though, it's pretty obvious. Hence I suppose why it's only a mark.
Post by: scocliffe09 on May 23, 2011, 05:08:51 pm
So more of just a query, but do people learn about which indicators to use for different titrations, or are you taught how to interpret/choose a suitable indicator.I know this won't quite answer your question, but what you need to know for unit 3 is that you need to choose an indicator so that the end point represents the equivalence point, i.e. so that the equivalence point is as close to the centre of the indicator's pH range (data book). Apart from that, I don't think you need to know anything else about indicators other than that they are weak acids and therefore could potentially affect acid/base titrations (but this is unlikely).
Also, while on indicators, if you had to choose between Phenolphthalein and Methyl Red as an indicator for a strong vs strong reaction, would any of them be better? By this I mean would it be better to look for a colourless -> red or red -> yellow? It probably sounds stupid, but just want to make sure I'm thinking straight :P
Post by: luken93 on May 23, 2011, 05:15:12 pm
Also, in the production of biodiesel, can you skip straight from the triglyceride to the 3 methyl esters? Or are you better off to say an intermediate reaction that breaks the triglyceride into 3 carboxcylic acids before reaction with methanol etc.
Post by: scocliffe09 on May 23, 2011, 05:23:10 pm
Cheers, that basically answers my question.better off breaking it down and being more detailed. you have the knowledge and understanding so it can't hurt.
Also, in the production of biodiesel, can you skip straight from the triglyceride to the 3 methyl esters? Or are you better off to say an intermediate reaction that breaks the triglyceride into 3 carboxcylic acids before reaction with methanol etc.
Post by: luken93 on May 24, 2011, 09:47:36 pm
Also, is it only when a pH isn't stated that we draw the regular amino acid (H2N - CHR - COOH)? The exam I did today said at neutral pH of 7, draw a dipeptide of two amino acids immediatly after a zwitterion question - but the answers didn't show the zwitterion form? Do dipeptides change this?
Post by: GuessWho on May 24, 2011, 10:05:33 pm
In regard to your other question, a neutral pH of 7 doesn't necessarily mean that the amino acid is in its zwitterion form. The pH at which an amino acid is in its zwitterion form is determined by its Z group.
I think if a pH isn't stated its probably safe not to add charges to the amino acid.
Can anyone back me up on this information as I am not sure.
Post by: Graphite on May 25, 2011, 01:18:01 pm
In reality you can only make these statements by comparing the pKa of the acid/base functional groups with the external pH. (pKa vary depending on its extended conjugation to other atoms.)
@Guesswho you made a good point. Never assume an amino acid only contains a carboxylic and amino group as the Z group may contrain acid/base functional groups.
Post by: VivaTequila on May 26, 2011, 03:23:20 pm
The ionisation of an acid/base depends on the pH conditions. I would assume for VCE if external pH<7 then you can assume the basic functional groups get protonated and pH>7 the acid functional groups get deprotonated. Is this always true? No.
In reality you can only make these statements by comparing the pKa of the acid/base functional groups with the external pH. (pKa vary depending on its extended conjugation to other atoms.)
@Guesswho you made a good point. Never assume an amino acid only contains a carboxylic and amino group as the Z group may contrain acid/base functional groups.
Does this mean we can get amino acids that contain Z groups with carbonate groups or something? Those are basic aren't they?
Post by: luken93 on May 31, 2011, 07:32:42 pm
I had a question that asked to show the formation of the fragment from the parent ion, but just wanted to confirm that's how it actually worked...
Post by: Mao on May 31, 2011, 10:32:13 pm
Typically, the ionization step only has enough energy to cleave one bond (generally a C-C, C-O or O-H bond, it is not strong enough to cleave C-H). You therefore don't have any 'subsequent' ionization after the initial ionization.
WRONG!
Post by: luken93 on May 31, 2011, 10:45:45 pm
The answer said:
CH3COOH+ --> CH3+ + COOH
Whereas I wrote:
CH3COOH + e- --> CH3+ + COOH + 2e-
Is mine necessarily wrong then? (probably hahah)
Post by: Vincezor on May 31, 2011, 10:59:06 pm
Cheers, the question was to show the formation of the m/z = 15 fragment from the parent ion (ethanoic acid)
The answer said:
CH3COOH+ --> CH3+ + COOH
Whereas I wrote:
CH3COOH + e- --> CH3+ + COOH + 2e-
Is mine necessarily wrong then? (probably hahah)
Hehe this reminds me of a question from Insight 2011 :S
But I wrote what you wrote, and I think that textbook does it like that as well.
Post by: luken93 on May 31, 2011, 11:05:16 pm
This was the only Q I got wrong, gotta find out if I'm right or not!
Post by: Mao on May 31, 2011, 11:18:03 pm
Sorry for the confusion.
Source: Skoog, Holler & Crouch, Principles of Instrumental Analysis 6ed, 2007, Brooks/Cole.
Some more elaboration:
There are different ways to ionize the molecule. And these different methods produce different results. The most commonly used instrument in modern labs are electron-impact (EI) MS, which promote fragmentation and is useful for organic molecules. In EI-MS, electrons are accelerated to ~10 times the bond energy, which can easily cleave the bond. However, since electrons have extremely low mass, its kinetic energy is relatively small, and upon impact not much momentum is transferred to the molecule. Instead, a lot of the excess energy in the ionizing electron is transferred to vibrational and rotational energy of the impacted molecule (molecular ion), which then dissipate this energy by fragmenting. Depending on the setup of the MS, several fragmentation steps can occur.
(which, makes your life a bit harder I guess, oops)
Typical fragmentation example:
1. Molecular ion formation:
2. Fragmentation:
(and so on)
An alternative is the field-ionization technique, which simultaneously ionizes everything. This is by using a special 'emitter', which extracts electrons from the analyte via quantum tunneling. This technique doesn't promote fragmentation, and isn't too useful for organic molecules. (There are 8 other techniques listed here on top of these two. zzzZZZ)
(and obviously, this is beyond VCE level. If I had to guess, I'd say third year level, maybe)
Post by: luken93 on May 31, 2011, 11:36:15 pm
Ah well, thanks for the very good explanation!
Post by: jane1234 on June 01, 2011, 06:04:35 pm
The relative masses in the data booklet are written (mostly) to 3 significant figures. If all the other values were 4 significant figures would you round to 3 or to 4? Because the exam I just did says 4, but I used a molecular mass that had 3 significant figures in it... ???
Post by: RobM8 on June 01, 2011, 06:39:18 pm
With sig figures:
The relative masses in the data booklet are written (mostly) to 3 significant figures. If all the other values were 4 significant figures would you round to 3 or to 4? Because the exam I just did says 4, but I used a molecular mass that had 3 significant figures in it... ???
I think it is because the masses are meant to be treated as a 'literary value', whereas the other data you are given is experiment data that someone has collected and isn't exact. Maybe literary value is not the best term but it is the best I can think of at the moment...
Post by: luken93 on June 01, 2011, 07:09:53 pm
I hate company exams, period.
Post by: jane1234 on June 01, 2011, 07:12:05 pm
I hate company exams, period.
Couldn't agree more!! :)
Do you know if VCAA would take the number of significant figures of the molecular masses into account??
Post by: luken93 on June 01, 2011, 07:38:34 pm
I doubt they'd be that nice hahaI hate company exams, period.
Couldn't agree more!! :)
Do you know if VCAA would take the number of significant figures of the molecular masses into account??
Was it dividing/multiplying or add/minus? Just making sure it was sig figs and not decimal places...
Post by: nacho on June 01, 2011, 07:42:54 pm
I just want to make sure i don't lose any marks because of sig figs.
Post by: luken93 on June 01, 2011, 07:51:57 pm
Wasn't there a post somewhere giving the rules of sig figs?If multiplying/dividing, round to the least number of sig figs
I just want to make sure i don't lose any marks because of sig figs.
2.01 x 3.0 = 6.0
If adding/subtracting, round to the least number of decimal places
245.1 + 20.001 = 265.1
Zeroes placed before other digits are not significant
0.0023 = 2 sig figs
Zeroes placed between other digits are significant
0.0203 = 3 sig figs
Zeroes placed after other digits are significant.
0.00230 = 3 sig figs
Post by: nacho on June 01, 2011, 08:08:21 pm
And, also..
If we are working out, do we need to give answers in sig figs?
Eg, a certain question asks for the mol of element X when we know that:
A + 2B ---> 3AB
And the question says, molar mass of A= 1.001, B = 3.50
and that 5 grams of B completely reacted with excess 'A'.
would i go:
n(AB) = n2/3(B)
n(B) = 3.5/5 = .... <---- does this have to be in sig figs?
therefore n(AB) = .... <---- or is it only this answer which is in sig figs?
tyvm
Post by: pi on June 01, 2011, 08:12:54 pm
How about the rules for what number of sig figs to use, when presented with information from the question.
And, also..
If we are working out, do we need to give answers in sig figs?
Eg, a certain question asks for the mol of element X when we know that:
A + 2B ---> 3AB
And the question says, molar mass of A= 1.001, B = 3.50
and that 5 grams of B completely reacted with excess 'A'.
would i go:
n(AB) = n2/3(B)
n(B) = 3.5/5 = .... <---- does this have to be in sig figs?
therefore n(AB) = .... <---- or is it only this answer which is in sig figs?
tyvm
Just the final answer is appropriate. Although, I like to maintain sig figs through steps, however it is not marked, just the answer.
Post by: luken93 on June 01, 2011, 08:19:40 pm
Also, your final answer is to the sig figs of your starting data only ie what is contained in the question itself?
Post by: nacho on June 01, 2011, 08:22:46 pm
why not good old 'round to two d.p'
so much damn easier. sig figs are unnecessarily confusing..
Post by: Graphite on June 02, 2011, 09:37:30 am
Its good in case you stuff up, you don't have to do something again
Post by: VivaTequila on June 02, 2011, 12:07:43 pm
If you want just write like as many numbers as you feel comfortable then next line write sig figs
Its good in case you stuff up, you don't have to do something again
When writing my answers, I always include at least 5 sig figures, and show these in my working. I get to a final answer and write =3.3913g for instance, and then directly under it, I always without fail write =3.39g w/ sig fig.
Hasn't failed me yet and it's been endorsed by everyone I've asked. Always circle the final answer though if you use this method.
Post by: EvangelionZeta on June 02, 2011, 08:29:54 pm
Post by: luken93 on June 05, 2011, 09:29:16 pm
Would the H come off the O, since it next to a more EN atom in oxygen, or is it just as likely to come off any other carbon atom?
Post by: b^3 on June 05, 2011, 09:38:59 pm
Post by: thatricksta on June 06, 2011, 08:15:34 am
Cheers, the question was to show the formation of the m/z = 15 fragment from the parent ion (ethanoic acid)
The answer said:
CH3COOH+ --> CH3+ + COOH
Whereas I wrote:
CH3COOH + e- --> CH3+ + COOH + 2e-
Is mine necessarily wrong then? (probably hahah)
Both are correct and will get you full marks (apparently this has been confirmed by the chief assessor) according to TSFX
I lurked around on this post (hopefully I didn't miss my answer) and was wondering if VCAA significant figures will take into account the molecular masses. It has been noted that most of the elements in our data booklet are rounded to 3 sig figures, so if we had a question (obviously not this easy) that involved us simply finding the mol of atoms in a particular mass that was weighed to be 4 sig figures, 2.514g it was something like... Calcium which has a molar mass of 40.1, would be then round our answer to 3 sig figures? (0.0627) or 4 sig figures? (0.06269)
Thanks
Post by: luken93 on June 06, 2011, 04:18:22 pm
Post by: thatricksta on June 06, 2011, 08:23:38 pm
Yep, still 3 sig figs, as molar mass is still a measurement that comes with significant figures.
Thanks.
My chemistry teacher still thinks it might be 4 sig figures as you should only take uncertainties within the question... I wonder if VCAA will actually treat us like that though... I have never actually had to make the decision in a practice exam
Post by: DavidSheena on June 06, 2011, 08:40:35 pm
1) Name a functional group present in all four nitrogen bases found in DNA.
The answer was Amine but I thought it would be carbonyl because in the data book I couldn't determine the amine group present on thymine.
2)Gravimetric analysis: why where multiple weighings of the precipitate formed?
ANS: Ensure precipitate was dry.
I wrote to acheive constant mass. Would that be acceptable?
3)How would an appropriate wavelength be determined for AAS analysis?
The answer didn't state anything about cathode lamps. And it was a bit too all over the place to understand.
Post by: Vincezor on June 06, 2011, 08:51:38 pm
1) Name a functional group present in all four nitrogen bases found in DNA.
The answer was Amine but I thought it would be carbonyl because in the data book I couldn't determine the amine group present on thymine.
There is no carbonyl functional group in the adenine base? :S. Sorry I'll have to leave this for others to answer.
2)Gravimetric analysis: why where multiple weighings of the precipitate formed?
ANS: Ensure precipitate was dry.
I wrote to acheive constant mass. Would that be acceptable?
I'd say so. constant mass is achieved when the precipitate is fully dried.
3)How would an appropriate wavelength be determined for AAS analysis?
The answer didn't state anything about cathode lamps. And it was a bit too all over the place to understand.
:S Question sounds like something you'd ask in UV-Vis analysis. What exam was this? For AAS you'd use the appropriate hollow cathode lamp for the metal being analysed, so I'm not sure what else you need to say...
Post by: luken93 on June 06, 2011, 09:01:07 pm
2) Yeah, I'd say yours is better than the answer
3) What Vince said.
Overall, it was a shit exam. Take their answers/questions with not too much thought.
Post by: tony3272 on June 06, 2011, 09:06:08 pm
Post by: nacho on June 06, 2011, 09:09:55 pm
Post by: Matt-Ong on June 06, 2011, 09:17:25 pm
Question 3:
Which of the following statements is incorrect?
B. The oxidation number of N in NH3 is -1/3
D. The oxidation number of H is LiAlH4 is +1
The answer says D and that the oxidation number can be a fraction.
I know that the oxidation number can be a fraction, but if N = -1/3, and H = +1, then won't the charge be 8/3?
Post by: DavidSheena on June 06, 2011, 09:18:27 pm
And for question 3. It was UV-Vis; read it wrong. Excuse my stupidity :P. But what would the answer be for UV- Vis?
Post by: nacho on June 06, 2011, 09:19:09 pm
Thanks for clearing up Quesiton One. My bad it clearly isn't carbonyl, I was thinking of C=C. Some random exam said that C=C was a functional group present in nucleotides.you keep picking wave lengths until a maximum abosrbance is determined... i think
And for question 3. It was UV-Vis; read it wrong. Excuse my stupidity :P. But what would the answer be for UV- Vis?
TSFX 2009 Examthere must be a mistake.. It would be -3 for N.
Question 3:
Which of the following statements is incorrect?
B. The oxidation number of N in NH3 is -1/3
D. The oxidation number of H is LiAlH4 is +1
The answer says D and that the oxidation number can be a fraction.
I know that the oxidation number can be a fraction, but if N = -1/3, and H = +1, then won't the charge be 8/3?
Hydrogen's oxidation number is always +1, except for metal hydrides, if i am not mistaken?
__ _ _ _
go call mao someone..
Post by: thatricksta on June 06, 2011, 09:45:29 pm
I have a few questions
1) Name a functional group present in all four nitrogen bases found in DNA.
The answer was Amine but I thought it would be carbonyl because in the data book I couldn't determine the amine group present on thymine.
2)Gravimetric analysis: why where multiple weighings of the precipitate formed?
ANS: Ensure precipitate was dry.
I wrote to acheive constant mass. Would that be acceptable?
3)How would an appropriate wavelength be determined for AAS analysis?
The answer didn't state anything about cathode lamps. And it was a bit too all over the place to understand.
I believe I just finished this exam and it mentions of a PURPLE organic compound, its corresponding wavelength will be YELLOW, i do not know the wavelength of this by heart... the exam overall (NEAP 2008 I assume) is not a very good one, its full of junk
I wrote the same answer for question two and thought it was significantly better than theirs!
Post by: Matt-Ong on June 06, 2011, 09:50:35 pm
there must be a mistake.. It would be -3 for N.
Hydrogen's oxidation number is always +1, except for metal hydrides, if i am not mistaken?
That's what I thought as well.. NH3 is definitely not a metal hydride.. So.. TSFX got it wrong?
Post by: thatricksta on June 06, 2011, 10:02:27 pm
B) "Does the information provided about experiment 2 allow you to state the functional group present in the compound?
I wrote:
Yes. The IR spectrum indicates a C=O bond. The compound reacts with NaOH which is a base, indicating that the compound is an acid. Therefore it will have a carboxyl functional group
NEAP answer:
"The band at 1700 is due to the carbonyl group. As this group is present in both esters and carboxylic acids (and other groups such as amides, aldehydes and keytones), we cannot be sure which functional group is present."
Who is correct? Can someone please explain this to me? Do I not understand the significance of the titration in this experiment? THANKS!
Post by: thatricksta on June 06, 2011, 10:10:42 pm
"How would an appropriate wavelength be determined for this analysis?"
This is in respect to an experiment using "spectroscopy" (not specified) and indicates that the compound being tested is "bore water", containing iron (we are determining the concentration of Fe in the bore water), which is first added to ferrozine to form a PURPLE complex. It goes on to suggest "their absorbances were determined in a spectrometer using an appropriate wavelength of light" (which I would assume corresponds to UV-Visible spec??)
NEAP writes its answer as:
A graph of the absorbance versus wavelength for a solution of iron/ferrozine complex would be obtained (1 mark)
The absorbance of maximum wavelength would be chosen (provided that no other component of bore water sample absorbed this wavelength) (1 mark)
ME:
I straight away recognised the complimentary colour yellow and wrote that
Yellow would be used as it is complimentary to purple.
Is my answer OK? Or is it straight up WRONG?
Thank you
Post by: nacho on June 06, 2011, 10:15:21 pm
Also, the final question on this exam statesto be honest, i would have put what the neap answers suggested (as stated in my previous post)
"How would an appropriate wavelength be determined for this analysis?"
This is in respect to an experiment using "spectroscopy" (not specified) and indicates that the compound being tested is "bore water", containing iron (we are determining the concentration of Fe in the bore water), which is first added to ferrozine to form a PURPLE complex. It goes on to suggest "their absorbances were determined in a spectrometer using an appropriate wavelength of light" (which I would assume corresponds to UV-Visible spec??)
NEAP writes its answer as:
A graph of the absorbance versus wavelength for a solution of iron/ferrozine complex would be obtained (1 mark)
The absorbance of maximum wavelength would be chosen (provided that no other component of bore water sample absorbed this wavelength) (1 mark)
ME:
I straight away recognised the complimentary colour yellow and wrote that
Yellow would be used as it is complimentary to purple.
Is my answer OK? Or is it straight up WRONG?
Thank you
I wouldnt think your answer would get the mark, UNLESS you added what wavelength of light 'yellow' occurs at. Yellow is a colour, not a wavelength.
And complimentary colours/corresponding wavelengths are not in the study design AFAIK.
hopefully someone can verify what i've said
Post by: Water on June 06, 2011, 10:25:19 pm
Post by: luken93 on June 06, 2011, 10:41:27 pm
NEAP 2008 has a question which specifies that C4H604 will have an IR band at 1700 which indicates a C=O bond, it then also states that 0.134g dissolved in water is titrated with a standardised 0.106 M NaOH solution. A titre of 21.43 was required to reach the end point.
B) "Does the information provided about experiment 2 allow you to state the functional group present in the compound?
"In experiment 2, the infrared spectrum of the compound was obtained. The spectrum included a band at a
wavenumber of approximately 1700 cm -1 ."
Experiment 2 is only the IR, you're jumping ahead of yourself. :P
Also, the final question on this exam statesNah, I wouldn't say you'd get the mark either. The important aspect of choosing a wavelength is that it is a) Strong absorbance, and b) No other compounds absorb strongly at this wavelength. As for complimentary colours, although it may absorb strongly, it's not necessarily true that it would be the best.
"How would an appropriate wavelength be determined for this analysis?"
This is in respect to an experiment using "spectroscopy" (not specified) and indicates that the compound being tested is "bore water", containing iron (we are determining the concentration of Fe in the bore water), which is first added to ferrozine to form a PURPLE complex. It goes on to suggest "their absorbances were determined in a spectrometer using an appropriate wavelength of light" (which I would assume corresponds to UV-Visible spec??)
NEAP writes its answer as:
A graph of the absorbance versus wavelength for a solution of iron/ferrozine complex would be obtained (1 mark)
The absorbance of maximum wavelength would be chosen (provided that no other component of bore water sample absorbed this wavelength) (1 mark)
ME:
I straight away recognised the complimentary colour yellow and wrote that
Yellow would be used as it is complimentary to purple.
Is my answer OK? Or is it straight up WRONG?
Thank you
Post by: thatricksta on June 06, 2011, 10:43:24 pm
NEAP 2008 has a question which specifies that C4H604 will have an IR band at 1700 which indicates a C=O bond, it then also states that 0.134g dissolved in water is titrated with a standardised 0.106 M NaOH solution. A titre of 21.43 was required to reach the end point.
B) "Does the information provided about experiment 2 allow you to state the functional group present in the compound?
"In experiment 2, the infrared spectrum of the compound was obtained. The spectrum included a band at a
wavenumber of approximately 1700 cm -1 ."
Experiment 2 is only the IR, you're jumping ahead of yourself.Also, the final question on this exam statesNah, I wouldn't say you'd get the mark either. The important aspect of choosing a wavelength is that it is a) Strong absorbance, and b) No other compounds absorb strongly at this wavelength. As for complimentary colours, although it may absorb strongly, it's not necessarily true that it would be the best.
"How would an appropriate wavelength be determined for this analysis?"
This is in respect to an experiment using "spectroscopy" (not specified) and indicates that the compound being tested is "bore water", containing iron (we are determining the concentration of Fe in the bore water), which is first added to ferrozine to form a PURPLE complex. It goes on to suggest "their absorbances were determined in a spectrometer using an appropriate wavelength of light" (which I would assume corresponds to UV-Visible spec??)
NEAP writes its answer as:
A graph of the absorbance versus wavelength for a solution of iron/ferrozine complex would be obtained (1 mark)
The absorbance of maximum wavelength would be chosen (provided that no other component of bore water sample absorbed this wavelength) (1 mark)
ME:
I straight away recognised the complimentary colour yellow and wrote that
Yellow would be used as it is complimentary to purple.
Is my answer OK? Or is it straight up WRONG?
Thank you
I thought experiment two was the entire experiment =/
Miss reading the question = fail
Thanks for the help :)
Post by: jane1234 on June 06, 2011, 10:47:10 pm
Yeah bitch! One of the Companies discretely added the complementary colour and I was LIKE ASJFGASKJGASJKFAJSGAHGSJKG, your screwing with me right? I have to know complementary colours. Lolol. When I did two VCAA Exams, I realized, I didn't need to :).
It's assumed knowledge.
From Year 7 art :D
And yeah, best absorbance is not necessarily the complementary colour, as you have to consider the other components of the solution that may also absorb it. This has tripped me up a fair few times :(
Post by: nacho on June 06, 2011, 10:58:54 pm
are we required to know that a nickel catalyst is present in hydrogenation from ethene to ethane?
and do we need to know states of catalysts involved in reaction pathways?
Also, if our reaction pathway is efficient, but a bit longer than the suggested one
eg: ethene to ethane to chloroethane to ethanol
as opposed to ethene to ethanol
would we be marked down?
Post by: luken93 on June 06, 2011, 11:04:22 pm
As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..
Post by: scocliffe09 on June 06, 2011, 11:05:55 pm
Yeah, you need to know catalysts for them.Yes I agree - it's best to know both pathways, because you might have to use either.
As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).
Post by: nacho on June 06, 2011, 11:07:03 pm
Books do not have any listed
thanks
Post by: thatricksta on June 06, 2011, 11:10:53 pm
Yeah, you need to know catalysts for them.Yes I agree - it's best to know both pathways, because you might have to use either.
As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).
Why is H2SO4 not (aq)? It is only 98% pure at the most I believe
Post by: luken93 on June 06, 2011, 11:13:02 pm
are there any catalysts present in the substitution reaction when forming an alcohol from a chloroalkane?PCl5
Books do not have any listed
thanks
Post by: jane1234 on June 06, 2011, 11:19:27 pm
Nah just NaOH or KOH as reactants I'm fairly sure.are there any catalysts present in the substitution reaction when forming an alcohol from a chloroalkane?PCl5
Books do not have any listed
thanks
luken93, I think PCl5 is only used for synthesising chloroalkanes from alcohols, could be wrong though...
Post by: RobM8 on June 06, 2011, 11:20:11 pm
Yeah, you need to know catalysts for them.Yes I agree - it's best to know both pathways, because you might have to use either.
As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).
Why is H2SO4 not (aq)? It is only 98% pure at the most I believe
It would work the reaction backward if it was aqueous.
Post by: luken93 on June 06, 2011, 11:20:53 pm
Woops, read it te other way around :SNah just NaOH or KOH as reactants I'm fairly sure.are there any catalysts present in the substitution reaction when forming an alcohol from a chloroalkane?PCl5
Books do not have any listed
thanks
luken93, I think PCl5 is only used for synthesising chloroalkanes from alcohols, could be wrong though...
Yeah, NaOH in that case :P
Post by: RobM8 on June 06, 2011, 11:22:19 pm
Post by: luken93 on June 06, 2011, 11:23:38 pm
Luken is alkanol ---> chloroalkane for VCE or Uni Chem?Either/Both AFAIK, I don't see any reason why you can't?
Post by: thatricksta on June 06, 2011, 11:29:45 pm
Yeah, you need to know catalysts for them.Yes I agree - it's best to know both pathways, because you might have to use either.
As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).
Why is H2SO4 not (aq)? It is only 98% pure at the most I believe
It would work the reaction backward if it was aqueous.
Thanks, its just used as a dehydrating agent, so we would have to use pure H2SO4 yes? (does this even exist??)
Or do impurities caused by metals not affect the reaction? (sorry if this doesn't make sense, I'm finding it very difficult to explain)
- I am going to bed and will check answer tomorrow morning, thanks for the help
Post by: Shark 774 on June 06, 2011, 11:53:42 pm
Post by: RobM8 on June 07, 2011, 12:03:23 am
Why can't non-metals be analysed by AAS?
They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.
Post by: scocliffe09 on June 07, 2011, 12:38:39 am
That's not necessarily true...Why can't non-metals be analysed by AAS?
They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!
Post by: RobM8 on June 07, 2011, 10:30:53 am
I always was told that they didn't produce visible light by our teacher - that is a worry.That's not necessarily true...Why can't non-metals be analysed by AAS?
They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?
Post by: nacho on June 07, 2011, 10:37:51 am
I think it may have something to do with electrical conductivity, pretty sure we don't need to know why though, it would seem like we're dwelling back into unit 1 and 2 and going ahead to 4..I always was told that they didn't produce visible light by our teacher - that is a worry.That's not necessarily true...Why can't non-metals be analysed by AAS?
They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?
edit:
Why is the light in AAS pulsed?
Post by: jane1234 on June 07, 2011, 03:58:58 pm
I think it may have something to do with electrical conductivity, pretty sure we don't need to know why though, it would seem like we're dwelling back into unit 1 and 2 and going ahead to 4..I always was told that they didn't produce visible light by our teacher - that is a worry.That's not necessarily true...Why can't non-metals be analysed by AAS?
They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?
edit:
Why is the light in AAS pulsed?
To differentiate between the light absorbed by the sample and the light emitted from the sample, as they will be of the same wavelength.
Post by: tony3272 on June 07, 2011, 04:01:08 pm
It's pulsed so that light which is emitted when the electron moves back from it's excited state is not read by the detector, I think.I think it may have something to do with electrical conductivity, pretty sure we don't need to know why though, it would seem like we're dwelling back into unit 1 and 2 and going ahead to 4..I always was told that they didn't produce visible light by our teacher - that is a worry.That's not necessarily true...Why can't non-metals be analysed by AAS?
They absorb and emit light/radiation that is not in the visible part of the electromagnetic spectrum.
It's more to do with the fact that we can't produce Hollow Cathode Lamps for them (and this is the hallmark of AAS that gives it specificity and accuracy) and that we might not be able to vaporise them successfully. e.g. most organic chemicals will be combusted by a flame!
Why is it that we can't produce Hollow Cathode Lamps for non-metals ?
edit:
Why is the light in AAS pulsed?
Post by: nacho on June 07, 2011, 07:27:35 pm
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam
Post by: luken93 on June 07, 2011, 07:36:09 pm
thanks,Pretty sure we don't, I thought the exact same thing!
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam
Post by: tony3272 on June 07, 2011, 07:39:21 pm
thanks,Lol i have no idea what that is...
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam
It seems more bio than chem. (btw which neap exam? I don't think i've seen that question)
Post by: nacho on June 07, 2011, 07:56:27 pm
these exam companies should never ever put things outside the syllabus.. it's completely demotivating and makes you think that you've missed out on some major aspect, or which wasnt covered by the textbook..thanks,Pretty sure we don't, I thought the exact same thing!
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam
Post by: Keo on June 07, 2011, 08:04:04 pm
I guess that's how these companies make money, make students think that harder questions which are totally irrelevant to the study design are actually better :tickedoff:these exam companies should never ever put things outside the syllabus.. it's completely demotivating and makes you think that you've missed out on some major aspect, or which wasnt covered by the textbook..thanks,Pretty sure we don't, I thought the exact same thing!
did we need to know that each amino acid is coded by 3 bases?
It came up in a neap exam
Post by: jane1234 on June 07, 2011, 11:18:31 pm
- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?
Post by: luken93 on June 07, 2011, 11:41:04 pm
- (Yet another sig fig question): When working out volumes of gases, does the number of significant figures in the temperature matter (using the nRT=PV formula)??Ummm, well I suppose it does, however when you are converting from celcius to kelvin, it'll be say 25 + 273 = 298. Addition means to the least number of DECIMAL places...
- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?
As for combustion, I thought all of the reactants and products were (g) ? Grr I hate states!
Post by: scocliffe09 on June 08, 2011, 01:08:12 am
Seriously guys, chill about sig figs. In the sf question, VCAA should make it pretty clear what's going on. And temperature is a bit of a contentious topic. My advice would be include it in your considerations but don't forget Luke's point.- (Yet another sig fig question): When working out volumes of gases, does the number of significant figures in the temperature matter (using the nRT=PV formula)??Ummm, well I suppose it does, however when you are converting from celcius to kelvin, it'll be say 25 + 273 = 298. Addition means to the least number of DECIMAL places...
- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?
As for combustion, I thought all of the reactants and products were (g) ? Grr I hate states!
Combustion is safest when written with gaseous states. depending on other reaction conditions, other states might be acceptable. For example, it is common for liquid water to form on the inside of a test tube so I don't see why writing (l) for water would be wrong.
Post by: thatricksta on June 08, 2011, 08:10:29 am
- (Yet another sig fig question): When working out volumes of gases, does the number of significant figures in the temperature matter (using the nRT=PV formula)??
- Also, when writing combustion equations, is it acceptable to write the organic compound in the gaseous (g) state?
Just DO NOT write aqueous and you should be ok.
Also, it's unlikely something like this would be asked, but if you were asked for the combustion of glucose (organic molecule), it would be solid, but that is common sense and I am sure you wouldn't write glucose as a gaseous state before combustion... xD
Question:
Do we need to include heat above the arrow of our equation for combustion reactions?
Post by: thushan on June 08, 2011, 08:30:41 am
Post by: nacho on June 08, 2011, 12:11:54 pm
2methyl-propan-1-ol be accepted if the given answers are:
• methylpropan–1–ol
• methyl–1–propanol
• 2–methyl–1–propanol
Post by: Water on June 08, 2011, 12:21:49 pm
From 2008 VCAA.
4-aminophenol absorbs less strongly than paracetamol onto the stationary phase of this TLC plate. Predict whether the Rf Value of 4-aminophenol in this analysis is greater or smaller than that of paracetamol, giving a reason for your choice.
My Answer: Greater than paracatamol as 4-aminophenol would desorb greater than adsorb thereby move along the mobile phase easier.
VCAA Answer: Greater, moves further from origin.
Would my answer be correct xD?
1 mark question btw.
Post by: RobM8 on June 08, 2011, 12:23:25 pm
• methylpropan–1–ol
• methyl–1–propanol
are correct as it is wrong nomenclature to put a 2 in front of the methyl - as it is the only place that it can occupy.
Post by: RobM8 on June 08, 2011, 12:28:14 pm
Water's question
From 2008 VCAA.
4-aminophenol absorbs less strongly than paracetamol onto the stationary phase of this TLC plate. Predict whether the Rf Value of 4-aminophenol in this analysis is greater or smaller than that of paracetamol, giving a reason for your choice.
My Answer: Greater than paracatamol as 4-aminophenol would desorb greater than adsorb thereby move along the mobile phase easier.
VCAA Answer: Greater, moves further from origin.
Would my answer be correct xD?
Your answer is messy but it is essentially saying the same thing.
I wouldn't say it desorbs greater than adsorbs...
Maybe 'Greater than paracatamol as 4-aminophenol does not adsorb to the stationary phase as strongly and hence spends more time in the mobile phase resulting in greater displacement from the origin and a higher Rf value'.
Post by: jasoN- on June 08, 2011, 12:38:54 pm
Nacho, onlyno clue why they didn't just call it 2-butanol
• methylpropan–1–ol
• methyl–1–propanol
are correct as it is wrong nomenclature to put a 2 in front of the methyl - as it is the only place that it can occupy.
Post by: RobM8 on June 08, 2011, 12:42:04 pm
C
|
C-C-C is different to C-C-C-C
Post by: nacho on June 08, 2011, 12:42:14 pm
Nacho, only
• methylpropan–1–ol
• methyl–1–propanol
are correct as it is wrong nomenclature to put a 2 in front of the methyl - as it is the only place that it can occupy.
the 2-methyl-1-propanol is the answer given by vcaa, and the methyl group could hang off the first carbon atom
except i was just wondering
since i wrote 2-methyl, am i incorrect in saying propan-1-ol and should i have to say 1-propanol
also, yea water your ans is correct, except just being pedantic - it technically doesnt move along the mobile phase, it just bonds to the mobile phase - doesn't it? (wait, is that the same thing?...)
It moves up the stationary phase, i would just say 'further away from the origin'
btw, what mark did u get on 08, water? :D
Post by: Water on June 08, 2011, 12:48:27 pm
+ for that question, I marked it wrong because it didn't align with VCAAs, not sure if I was being too harsh.
Post by: RobM8 on June 08, 2011, 12:49:40 pm
Why? There is only one possible carbon for the methyl to be on?
The methyl group can't be on the first carbon atom otherwise it becomes butanol ?
To answer the original aim of your question: propan-1-ol and 1-propanol are saying the same thing.
Post by: luken93 on June 08, 2011, 12:52:08 pm
Post by: Water on June 08, 2011, 12:52:52 pm
Is the IO4- (aq) ion acting as an oxidant or reductant? Explain your choice.
My Answer: Oxidant, as it causes the reduction reaction.
VCAA: Oxidant, the oxidation number of I decreases from +7 to +5.
Was my answer too herpy derpy? It is another 1 mark question. I Don't know when the VCAA wants a general answer or a deep answer. God >_<!
Post by: RobM8 on June 08, 2011, 12:58:13 pm
Yeah, but the assessor's have stated that as long as it is named within the IUPAC ruling and is clear what you are naming, it isn't wrong. Hence. you are able to put 2-methyl or just methyl - as both imply the same meaning.Yeah.
Always give specific answers Water; it is a minor discrepancy but you have given a very general reason and have more said what an oxidant does not why the ion is acting as an oxidant.
Post by: nacho on June 08, 2011, 12:59:47 pm
i got every aspiriin question wrong, we never did an aspirin SAC, our last sac was on polymers..
4 multiple choice errors, that def could have been handled better..
just realised, that it would indeed be butanol, hm..
uh in regards to your oxidation quesiton, i think its always best to write like what it reduces, or that there is a change in the oxidation number
can we use 'hydrogen environments' and 'proton environments' interchangebly?
Post by: RobM8 on June 08, 2011, 01:07:22 pm
1H = a proton.
Post by: luken93 on June 08, 2011, 01:08:37 pm
damn, ya beat me by 1 mark..I'd say 1H environments to be safe :P
i got every aspiriin question wrong, we never did an aspirin SAC, our last sac was on polymers..
4 multiple choice errors, that def could have been handled better..
just realised, that it would indeed be butanol, hm..
uh in regards to your oxidation quesiton, i think its always best to write like what it reduces, or that there is a change in the oxidation number
can we use 'hydrogen environments' and 'proton environments' interchangebly?
A new question, from the 2008 VCAA.Yeah, to be safe always include the oxidation number - in doing so you're confirming the answer with yourself anyway :)
Is the IO4- (aq) ion acting as an oxidant or reductant? Explain your choice.
My Answer: Oxidant, as it causes the reduction reaction.
VCAA: Oxidant, the oxidation number of I decreases from +7 to +5.
Was my answer too herpy derpy? It is another 1 mark question. I Don't know when the VCAA wants a general answer or a deep answer. God >_<!
Post by: jasoN- on June 08, 2011, 01:09:02 pm
Because methylpropan-1-ol and butan-2-ol are structural isomersC
C
|
C-C-C is different to C-C-C-C
|
C-C-C that's not the carbon backbone of methylpropan-1-ol (that would be the backbone of 2-methylpropanol)
C OH
| |
C-C-C this is methylpropan-1-ol.. also known as butan-2-ol: C-C-C-C
| anyway i dunno why vcaa would name it like methylpropan-1-ol
OH
Post by: nacho on June 08, 2011, 01:11:18 pm
is accepted, correct?
I hate Ramine
eg aminoethane over ethanamine
Post by: luken93 on June 08, 2011, 01:11:22 pm
wouldWe are talking about 2-MethylPropan-1-ol
2methyl-propan-1-ol be accepted if the given answers are:
• methylpropan–1–ol
• methyl–1–propanol
• 2–methyl–1–propanol
The reason why it is stated as methyl only, is because if you were to put a methyl on a propane chain, the only place it can be put is on the 2-C, hence the debate if you need to bother adding the 2. In essence, it's the same as saying 1-Butanoic Acid, because we know that a carboxyl group has to be on the 1st carbon, but neither are penalised.
Post by: luken93 on June 08, 2011, 01:12:14 pm
2-butanamine
2-butylamine
Post by: jane1234 on June 08, 2011, 01:13:34 pm
aminoR
is accepted, correct?
I hate Ramine
eg aminoethane over ethanamine
TSFX said that only the latter is correct.
So, to be on the safe side I'd always write R-amine.
Then again, TSFX could be wrong :P
Post by: jasoN- on June 08, 2011, 01:13:46 pm
still i myself wouldn't accept methylpropanol to be the same as 2-methylpropanol.
Post by: nacho on June 08, 2011, 01:19:05 pm
yea, that's what the P2G lecturer said (taught at macrob) and she explicitly mentioned that VCAA said not to write amino..aminoR
is accepted, correct?
I hate Ramine
eg aminoethane over ethanamine
TSFX said that only the latter is correct.
So, to be on the safe side I'd always write R-amine.
Then again, TSFX could be wrong :P
but, my tutor says that you can write amino.. and he got a 50, and probably has an IQ >130 .. so confused.
i got caught off guard by that one, i didnt realise it was on the same carbon backbone, otherwise i wouldnt have wrote 2-methyl..wouldWe are talking about 2-MethylPropan-1-ol
2methyl-propan-1-ol be accepted if the given answers are:
• methylpropan–1–ol
• methyl–1–propanol
• 2–methyl–1–propanol
The reason why it is stated as methyl only, is because if you were to put a methyl on a propane chain, the only place it can be put is on the 2-C, hence the debate if you need to bother adding the 2. In essence, it's the same as saying 1-Butanoic Acid, because we know that a carboxyl group has to be on the 1st carbon, but neither are penalised.
however... my original question was in regard to the placement of the number '1'
in propan-1-ol
is that accept? Or does it have to be 1-propanol
Post by: jasoN- on June 08, 2011, 01:22:43 pm
just make sure theres always - between numbers, and no - between words (for the most part, in some cases such as ethers, there may be spaces between words)
(ie. looking at what u wrote about 2methyl-propan-1-ol is technically incorrect, it shoul be 2-methylpropan-1-ol, don't know if vcaa penalises on these flaws though)
Post by: luken93 on June 08, 2011, 01:23:45 pm
btw, why so many people not at school?
Post by: luken93 on June 08, 2011, 01:24:18 pm
1-propanol = propan-1-ol both are equally acceptedwoops hahaha
just make sure theres always - between numbers, and no - between words
(ie. looking at what u wrote about 2methyl-propan-1-ol is technically incorrect, it shoul be 2-methylpropan-1-ol, don't know if vcaa penalises on these flaws though)
Post by: RobM8 on June 08, 2011, 01:24:57 pm
To answer the original aim of your question: propan-1-ol and 1-propanol are saying the same thing.
btw, why so many people not at school?
Spares
Post by: nacho on June 08, 2011, 02:32:44 pm
btw, why so many people not at school?got a chem exam in a week and an accounting exam in 6 days
Post by: scocliffe09 on June 08, 2011, 02:35:00 pm
yea, that's what the P2G lecturer said (taught at macrob) and she explicitly mentioned that VCAA said not to write amino..aminoR
is accepted, correct?
I hate Ramine
eg aminoethane over ethanamine
TSFX said that only the latter is correct.
So, to be on the safe side I'd always write R-amine.
Then again, TSFX could be wrong :P
but, my tutor says that you can write amino.. and he got a 50, and probably has an IQ >130 .. so confused.i got caught off guard by that one, i didnt realise it was on the same carbon backbone, otherwise i wouldnt have wrote 2-methyl..wouldWe are talking about 2-MethylPropan-1-ol
2methyl-propan-1-ol be accepted if the given answers are:
• methylpropan–1–ol
• methyl–1–propanol
• 2–methyl–1–propanol
The reason why it is stated as methyl only, is because if you were to put a methyl on a propane chain, the only place it can be put is on the 2-C, hence the debate if you need to bother adding the 2. In essence, it's the same as saying 1-Butanoic Acid, because we know that a carboxyl group has to be on the 1st carbon, but neither are penalised.
however... my original question was in regard to the placement of the number '1'
in propan-1-ol
is that accept? Or does it have to be 1-propanol
amino- as a prefix, if amine is the primary functional group, is NOT acceptable according to IUPAC naming, because the primary functional group must come last. the most acceptable naming is -anamine, and -ylamine is also acceptable (according to my teacher and the IUPAC naming system). As long as your naming is unambiguous and without obvious errors for VCE, you will get your marks.
Post by: luken93 on June 08, 2011, 02:40:52 pm
Also, I know this has been brought up, but if you're going to put the number in front of the name, do you have to do this for the whole naming?
ie 2-methylpropan-1-ol and
2-methyl-1-propanol
Post by: Water on June 08, 2011, 02:45:43 pm
Post by: nacho on June 08, 2011, 02:45:56 pm
they accepted:
aminoethane
ethylamine
ethanamine.
Post by: scocliffe09 on June 08, 2011, 02:51:10 pm
2008 vcaa assessment report:But just wait until they have an easy exam and need to spread the cohort (2008 was medium I think) - VCAA will change their minds... They do it on a regular basis for methods!
they accepted:
aminoethane
ethylamine
ethanamine.
Post by: luken93 on June 08, 2011, 03:29:15 pm
and numbering, should it be X-..ylamine and X-...anamine or??
Post by: nacho on June 08, 2011, 03:34:59 pm
I'm reading up on how it is produced, and i know how it blocks pain (as in how it attaches itself to the active site of the enzyme which oxidises the fatty acid to make that thing that sends pain messages to the brain)
is there anything else?
I didn't know it could be produced from ethanoic acid, the book only mentioned acetic anhydride
Post by: luken93 on June 08, 2011, 03:37:39 pm
Wouldn't hurt to know about ethanoic acid though.
Post by: nacho on June 08, 2011, 03:38:39 pm
Post by: luken93 on June 08, 2011, 03:41:33 pm
anything else about it?Not that I know of, only how it reacts, what it's made of, and the functional groups present I suppose. I've never seen it questioned in depth though, but then again, feel free to surprise me VCAA.
Post by: jane1234 on June 08, 2011, 03:43:20 pm
anything else about it?
I don't think you need to know in great detail how aspirin inhibits prostaglandin formation... that's bio stuff..
The main thing to be aware of is the synthesis reaction, the hydrolysis reaction and also be able to recognise the structure of aspirin and salicylic acid.
Wouldn't hurt to know the catalysts as well...
and @luken93 I think half the state gets Wednesdays or Wednesday afternoons off :P
Post by: luken93 on June 08, 2011, 03:45:57 pm
Post by: Water on June 08, 2011, 04:06:51 pm
Post by: jane1234 on June 08, 2011, 04:10:42 pm
But if you wanted to know:
The pH where a molecule (e.g. amino acid) has no net charge.
Okay concordant tires are +-0.05mL, yes?
So out of:
17.98mL
18.32mL
18.07mL
18.16mL
...there are no concordant tires right?
Lisachem thinks not, they say that 18.07mL, 18.16mL and 17.98mL are all concordant.
???
Post by: nacho on June 08, 2011, 04:13:43 pm
^I thought so too, that's what nelson chem says 0.05mL
But if you wanted to know:
The pH where a molecule (e.g. amino acid) has no net charge.
Okay concordant tires are +-0.05mL, yes?
So out of:
17.98mL
18.32mL
18.07mL
18.16mL
...there are no concordant tires right?
Lisachem thinks not, they say that 18.07mL, 18.16mL and 17.98mL are all concordant.
???
i've also heard that it is the closest three
just to be safe, if a q ever comes up, and they're not in 0.05 range, may as well put closest three
no one is going to expect an answer of
"There are no concordant results.."
Also:
Ammonia is a weak base, which ionises in water according to the equation
NH3(aq) + H2O(l) ---> NH4+(aq) + OH-(aq).
If 20 mL of 0.10 M NH3(aq) is added to 50 mL of water, which of the following correctly
describes the expected change in pH and number of ammonia molecules, i.e. N(NH3), present
due to the dilution.
A. pH increases, N(NH3) increases
B. pH decreases, N(NH3) increases
C. pH increases, N(NH3) decreases
D. pH decreases, N(NH3) decreases
Post by: Water on June 08, 2011, 04:17:44 pm
On note of things, speculation. Is this year's cohurt strong?
@Nacho, is it D?
Post by: jane1234 on June 08, 2011, 04:21:01 pm
Lisachem does their concordant results as +/- 0.10, perhaps?
On note of things, speculation. Is this year's cohurt strong?
Yeah that's what they said but what does VCAA define as concordant?
And no idea... I know my school cohort is heaps stronger than last year's though... even the teachers are saying it :)
Post by: thatricksta on June 08, 2011, 04:33:42 pm
Lisachem does their concordant results as +/- 0.10, perhaps?
On note of things, speculation. Is this year's cohurt strong?
Yeah that's what they said but what does VCAA define as concordant?
And no idea... I know my school cohort is heaps stronger than last year's though... even the teachers are saying it :)
I believe VCAA will define concordant results as within +/- 0.05mL of each other.
Post by: luken93 on June 08, 2011, 05:19:41 pm
Post by: luken93 on June 08, 2011, 05:23:59 pm
Assessor did mention that if the highest priority functional group is an amino, it should be
mentioned in the suffix, 2-aminobutane was accepted as an answer.
The IUPAC system is a series of guidelines (about 1000 pages of rules and notations) to
assist scientists in naming compounds. There are many acceptable variations in naming,
and therefore, the general rule is that if the name results in a unique compound, it is
acceptable! Saying that, the comment from the Chief Assessor last year (see below)
suggests that even though he says "amine should appear in the systematic name"
having the principle functional group in the suffix is becoming very important. In short -
use amine at the end of the name if the amino is the principle functional group, just to be
safe.
Quoted from TSFX
Post by: RobM8 on June 08, 2011, 05:28:29 pm
A teacher at our school who is an assessor says that they must be in 1% of each other.
He also said it is highly unlikely VCAA would give you a question with stupid titres, there would always be three titres that are very close to each other and 1 or 2 titres that are way off - like 0.5 mL higher or lower than the other three.
Post by: nacho on June 08, 2011, 05:37:09 pm
A. CH3CH2OH
B. CH3CH3
C. CH3CH2CH2OH
D. HOCH2CH2OH
okay i think its pretty obvious its not B..
But what about D? Is that a polar or is it symmetrical?
I did this question ages ago, and next to it, in pencil, i've written 'don't be tricked, - asymmetrical'
Post by: jane1234 on June 08, 2011, 05:40:12 pm
Which of the following molecules would be most soluble in water?
A. CH3CH2OH
B. CH3CH3
C. CH3CH2CH2OH
D. HOCH2CH2OH
okay i think its pretty obvious its not B..
But what about D? Is that a polar or is it symmetrical?
I did this question ages ago, and next to it, in pencil, i've written 'don't be tricked, - asymmetrical'
I'd think D as it has two polar functional groups - as opposed to A which only has one.
No idea if the symmetrical/asymmetrical factor has a big effect.
Post by: luken93 on June 08, 2011, 05:46:58 pm
As for cohorts, ours is far better than last year as well, however last year our highest score was 35 - so it shouldn't taake too much to beat that :P
Post by: nacho on June 08, 2011, 06:03:19 pm
Will it donate the proton in it's Z-group, or only the proton in its backbone?
Is this the same for when the environment is acidic, or basic?
Post by: Water on June 08, 2011, 06:12:36 pm
PS: Just consulted Heineman and Wikipedia.
Wikipedia: In chemistry, a zwitterion ( /ˈtsvɪtər.aɪ.ən/ tsvit-ər-eye-ən; from German zwitter [ˈtsvɪtɐ] "hybrid") is a molecule with a positive and a negative electrical charge (n.b. not dipoles) at different locations within that molecule. Zwitterions are sometimes also called inner salts.
Heineman : A dipolar ion formed when the proton of a carboxy group molecule is transferred to the amino functional group.
Post by: tony3272 on June 08, 2011, 06:27:00 pm
The Secondary COOH, will not be affected.In the exams i've done, the solutions say that they both donate a proton.
Post by: Andiio on June 08, 2011, 06:43:26 pm
Post by: thatricksta on June 08, 2011, 06:44:00 pm
The amino story: What is acceptable keeps on evolving, and although the Chief
Assessor did mention that if the highest priority functional group is an amino, it should be
mentioned in the suffix, 2-aminobutane was accepted as an answer.
The IUPAC system is a series of guidelines (about 1000 pages of rules and notations) to
assist scientists in naming compounds. There are many acceptable variations in naming,
and therefore, the general rule is that if the name results in a unique compound, it is
acceptable! Saying that, the comment from the Chief Assessor last year (see below)
suggests that even though he says "amine should appear in the systematic name"
having the principle functional group in the suffix is becoming very important. In short -
use amine at the end of the name if the amino is the principle functional group, just to be
safe.
Quoted from TSFX
just a note on this, yes in this specific case the Amino group is the highest priority, but it is exceeded by Carboxylic acids and alkenes.
I don't have the specific order with me :( sorry, but basically, if it doesn't sound right, it's probably not...
You aren't super likely to get a combination of high priority groups (not saying it cant happen though), but as a general rule, if its got COOH, NH2 or a double bonded carbon, I would be using the suffix's
We don't need to know about how Aspirin/Paracetamol specifically 'blocks' and alleviates pain...right?
No, but its possible that we might need to know that rational drug design is based on inhibiting active sizes of enzymes. This is very much a biology question, but I believe its possible for them to ask.
The Secondary COOH, will not be affected.In the exams i've done, the solutions say that they both donate a proton.
This was debated during the TSFX lecture and apparently both are acceptable.
Post by: luken93 on June 08, 2011, 07:00:09 pm
Post by: Water on June 08, 2011, 07:05:12 pm
Post by: luken93 on June 08, 2011, 07:19:35 pm
Post by: Greatness on June 08, 2011, 07:30:09 pm
'The net charge on a zwitterion is zero, so on aspartic acid it is only the alpha-COOH group which is deprotonated to COO-'
But i've been told by my teacher and read in exams and stuff that the side chains are affected in low/high Ph...
Post by: Water on June 08, 2011, 07:30:35 pm
Post by: Andiio on June 08, 2011, 07:40:20 pm
Obviously the normal NH2 and COOH groups would become protonated/de-protonated, but if you deprotonated the COOH in the Z-group, wouldn't the aspartic acid 'zwitterion' retain a negative charge? :\
Post by: Water on June 08, 2011, 07:44:22 pm
New Questions: From Jacaranda 2011.
The Victorian EPA has recently monitored an oil slick by sample. BY this means the agency was able to idenfy the ship that had ilegally discharged its bilge water into the bay. Which of the following combinations of instrumental analytical techniques would provide the most useful information to identify the hydrocarbons in the oil slick
a) IR and NMR
b) GC And Mass Spectroscopy
c) IR and AAS
d) UV-Vis and HPLC
My question is, why did Jacaranda said B? I said D.
Isn't Oil a liquid?
2nd Question.
A Chemical analyses a 5.0g ore sample of chalcopyrite, CuFeS2. A gravimetric analysis is carried out so that all the sulfur in CuFeS2 is precipitated as BaSO4. The amount of BaSO4 is determined to be 0.10mol. What is Percentage mass of sulfur in the ore?
a) 3.2%
b) 12.8%
c) 32%
d) 64%
Jacarandaa said 64% D , but I said 32%. Any working out to justify Jacaranda's answer.
I"m assuming its like CuFeS2 --> 2BaSO4
Post by: Mao on June 08, 2011, 07:49:43 pm
Since zwitterions are said to have a neutral charge, and if Z/side chain groups are affected, what would you draw if you had to draw say, the aspartic acid zwitterion in a pH of 7?
Obviously the normal NH2 and COOH groups would become protonated/de-protonated, but if you deprotonated the COOH in the Z-group, wouldn't the aspartic acid 'zwitterion' retain a negative charge? :\
That depends on the isoelectric point, which you are not required to know.
However, they could word it like "draw aspartic acid at pH=12", in which case the environment is too basic, and all groups deprotonate (net -2 charge).
[In reality, the side group of aspartic acid deprotonates at pH>2.77]
Post by: vea on June 08, 2011, 07:58:21 pm
Post by: Mao on June 08, 2011, 08:02:52 pm
New Questions: From Jacaranda 2011.
The Victorian EPA has recently monitored an oil slick by sample. BY this means the agency was able to idenfy the ship that had ilegally discharged its bilge water into the bay. Which of the following combinations of instrumental analytical techniques would provide the most useful information to identify the hydrocarbons in the oil slick
a) IR and NMR
b) GC And Mass Spectroscopy
c) IR and AAS
d) UV-Vis and HPLC
My question is, why did Jacaranda said B? I said D.
Isn't Oil a liquid?
Yes, oil in this case is a liquid. However hydrocarbons don't respond very well to UV-vis radiation unless they are conjugated (google carotene to see what this means). IR is mostly useless for hydrocarbons, since it gives functional group information but not too much on overall structure, so you will just see a whole bunch of C-C and C-H peaks. And NMR would only be useful if the mixture can be separated into pure fractions to analyse separately (NMR of mixtures can be ridiculously messy, as the peaks will overlap).
This question is testing a small section of the chromatography chapter, which briefly mentions GC can be paired with MS. With GC-MS, you can achieve a separation of components, as well as the mass spectrum of each components. The separation of components is important because a mixture of different hydrocarbons are present.
Post by: luken93 on June 08, 2011, 08:21:17 pm
So wait, in acidic/basic conditions the Z group is affected, yet as a zwitterion it isn't?Since zwitterions are said to have a neutral charge, and if Z/side chain groups are affected, what would you draw if you had to draw say, the aspartic acid zwitterion in a pH of 7?
Obviously the normal NH2 and COOH groups would become protonated/de-protonated, but if you deprotonated the COOH in the Z-group, wouldn't the aspartic acid 'zwitterion' retain a negative charge? :\
That depends on the isoelectric point, which you are not required to know.
However, they could word it like "draw aspartic acid at pH=12", in which case the environment is too basic, and all groups deprotonate (net -2 charge).
[In reality, the side group of aspartic acid deprotonates at pH>2.77]
aah chemistry is just getting worse by the minute
Post by: Andiio on June 08, 2011, 08:33:59 pm
Q: Asparagine is an amino acid that can be produced in the human body. Draw the structural formula of asparagine at pH 2.
I drew it with a protonated NH3+ group in the Z chain and also a 'normal' NH3+ in the a-amino acid... but the answers only drew it with the 'normal' NH3+ (i.e. NH3+CHCOOH)
:\ Am I right or..?
Post by: nacho on June 08, 2011, 08:35:21 pm
Since zwitterions are said to have a neutral charge, and if Z/side chain groups are affected, what would you draw if you had to draw say, the aspartic acid zwitterion in a pH of 7?WAIT, maybe, the NH2 goes to NH3+ from the carboxyl group in the main chain and then to NH42+ from the carboxyl group in the z-group?
Obviously the normal NH2 and COOH groups would become protonated/de-protonated, but if you deprotonated the COOH in the Z-group, wouldn't the aspartic acid 'zwitterion' retain a negative charge? :\
Or is my line of thought retarded?
Post by: taqi on June 08, 2011, 10:08:27 pm
i got 64%; since u know that its 0.1mol of BaSO4, you know theres a total of 0.1mol of S, so times that by Mr, 0.1x32.1=3.21g, so 3.21/5x100=64%
just what i think
Post by: Water on June 08, 2011, 10:11:09 pm
but for every 1 amount of sulfur in BaSO4 , and there is CuFeS2 , there shud be two amounts of sulfur in CuFeS2 to get that 1 amount?
Or Is my thinking wrong?
Post by: luken93 on June 08, 2011, 10:26:10 pm
Just some weird question from CSE:That exam is wrong, it should be protonated on both. I know this for a fact that the exam is wrong.
Q: Asparagine is an amino acid that can be produced in the human body. Draw the structural formula of asparagine at pH 2.
I drew it with a protonated NH3+ group in the Z chain and also a 'normal' NH3+ in the a-amino acid... but the answers only drew it with the 'normal' NH3+ (i.e. NH3+CHCOOH)
:\ Am I right or..?
Post by: Andiio on June 08, 2011, 10:53:01 pm
Just some weird question from CSE:That exam is wrong, it should be protonated on both. I know this for a fact that the exam is wrong.
Q: Asparagine is an amino acid that can be produced in the human body. Draw the structural formula of asparagine at pH 2.
I drew it with a protonated NH3+ group in the Z chain and also a 'normal' NH3+ in the a-amino acid... but the answers only drew it with the 'normal' NH3+ (i.e. NH3+CHCOOH)
:\ Am I right or..?
:[
Post by: dmanz on June 08, 2011, 10:58:17 pm
i know that if something is concentrated it means that the soluble particles are closer together.
Post by: davidle_10 on June 08, 2011, 11:06:42 pm
Post by: Andiio on June 08, 2011, 11:07:19 pm
Post by: davidle_10 on June 08, 2011, 11:09:47 pm
Post by: Andiio on June 08, 2011, 11:11:44 pm
I would think both phosphate or phosphate group would be acceptable, but i don't think you can call it as a phosphate ion
Haha I wrote phosphate group, according to NEAP it's a phosphate ion.
Post by: davidle_10 on June 08, 2011, 11:16:06 pm
Post by: Mao on June 09, 2011, 12:23:11 am
So wait, in acidic/basic conditions the Z group is affected, yet as a zwitterion it isn't?Since zwitterions are said to have a neutral charge, and if Z/side chain groups are affected, what would you draw if you had to draw say, the aspartic acid zwitterion in a pH of 7?
Obviously the normal NH2 and COOH groups would become protonated/de-protonated, but if you deprotonated the COOH in the Z-group, wouldn't the aspartic acid 'zwitterion' retain a negative charge? :\
That depends on the isoelectric point, which you are not required to know.
However, they could word it like "draw aspartic acid at pH=12", in which case the environment is too basic, and all groups deprotonate (net -2 charge).
[In reality, the side group of aspartic acid deprotonates at pH>2.77]
aah chemistry is just getting worse by the minute
Not sure what you mean. the zwitterion is also affected by the acid/base conditions. I do need to make a correction though, the side group of aspartic acid ionizes at pH>4 (roughly).
Here is a more detailed explanation:
We must consider the amino acid to be in some kind of equilibrium with its surroundings (unit 4 VCE + first year university). However, there are a few things we can know without learning all of that:
-Typically, acids and bases ionize over a pH range of 2. Acids and bases all have an 'acidic constant' Ka (unit 4 VCE), which corresponds to some pKa value. This can be considered to be the 'activation' point of the acid.
--When pH=pKa, the concentration of acid and its conjugate are equal.
--When pH=pKa-1 (i.e. environment is more acidic than the activation of the acid), the protonated form is 10x the concentration of the deprotonated form.
--When pH=pKa+1, the deprotonated form is 10x more concentrated than the protonated form. This transition is smooth.
-Consider the 2-amino acid group.
--The acid group typically have a pKa of ~2. Thus at pH of 3 or greater, it is always deprotonated. (at pH of 2 or slightly below it, a mixture of both deprotonated and protonated form exist)
--The amine group typically have a pKa of ~10. Thus at pH of 9 or less, it is always protonated.
--Combining the above, the zwitterion is dominant in the pH range of 3 to 9.
Consider aspartic acid, with a side group pKa of 3.6
pH=1: NH3+, COOH, Z-group COOH
pH=3: NH3+, COO-, Z-group COOH
pH=5: NH3+, COO-, Z-group COO-
pH=11: NH2, COO-, Z-group COO-
Post by: Lols123 on June 09, 2011, 07:38:29 am
What colour would the resulting mixture be in the presence of phenol red and thymol blue?
I dont get why it would be yellow for thymol blue :S wouldnt the resulting solution be slightly acidic, turning it red?
Post by: thatricksta on June 09, 2011, 08:20:58 am
I would think both phosphate or phosphate group would be acceptable, but i don't think you can call it as a phosphate ion
Haha I wrote phosphate group, according to NEAP it's a phosphate ion.
I wrote phosphate group on that exam, I wouldn't be stressed over that. I would be more concerned about naming the phosodiester xD
Post by: luken93 on June 09, 2011, 08:30:21 am
If an amino acid had the NH2 and COOH group off the 2-C, as well as an NH2 in the Z chain
At pH 2, NH3+, COOH, NH3+
At pH 7, NH3+, COO-, NH3+
At pH 12, NH2, COO-, NH2
And vice versa if it had a COOH group rather than an NH2
That's all I want to know :)
Post by: thushan on June 09, 2011, 08:55:02 am
Put it this way; in low pH there is a lot of H3O+ flying around, and H3O+ loves shoving protons into other things. So the NH2 and the COO- would have protons shoved in to form NH3+ and COOH.
In high pH there is a lot of OH- flying around, and OH- loves ripping protons off other things. So the amino group would have its extra proton taken to form -NH2 (from -NH3+) and carboxyl would have its proton ripped off to form COO- (from COOH).
Post by: luken93 on June 09, 2011, 09:11:07 am
You mean NH2 COO- NH2 for pH 12 in general luken.Haha I really should proof read my stuff :P
Put it this way; in low pH there is a lot of H3O+ flying around, and H3O+ loves shoving protons into other things. So the NH2 and the COO- would have protons shoved in to form NH3+ and COOH.
In high pH there is a lot of OH- flying around, and OH- loves ripping protons off other things. So the amino group would have its extra proton taken to form -NH2 (from -NH3+) and carboxyl would have its proton ripped off to form COO- (from COOH).
How're you feeling about today? :)
Post by: thushan on June 09, 2011, 10:30:50 am
Post by: nacho on June 09, 2011, 12:36:36 pm
Wait, at a pH of 3, why would the COOH group in the main chain donate it's proton? Shouldn't it just be the NH2 accepting protons to form NH3+?So wait, in acidic/basic conditions the Z group is affected, yet as a zwitterion it isn't?Since zwitterions are said to have a neutral charge, and if Z/side chain groups are affected, what would you draw if you had to draw say, the aspartic acid zwitterion in a pH of 7?
Obviously the normal NH2 and COOH groups would become protonated/de-protonated, but if you deprotonated the COOH in the Z-group, wouldn't the aspartic acid 'zwitterion' retain a negative charge? :\
That depends on the isoelectric point, which you are not required to know.
However, they could word it like "draw aspartic acid at pH=12", in which case the environment is too basic, and all groups deprotonate (net -2 charge).
[In reality, the side group of aspartic acid deprotonates at pH>2.77]
aah chemistry is just getting worse by the minute
Not sure what you mean. the zwitterion is also affected by the acid/base conditions. I do need to make a correction though, the side group of aspartic acid ionizes at pH>4 (roughly).
Here is a more detailed explanation:
We must consider the amino acid to be in some kind of equilibrium with its surroundings (unit 4 VCE + first year university). However, there are a few things we can know without learning all of that:
-Typically, acids and bases ionize over a pH range of 2. Acids and bases all have an 'acidic constant' Ka (unit 4 VCE), which corresponds to some pKa value. This can be considered to be the 'activation' point of the acid.
--When pH=pKa, the concentration of acid and its conjugate are equal.
--When pH=pKa-1 (i.e. environment is more acidic than the activation of the acid), the protonated form is 10x the concentration of the deprotonated form.
--When pH=pKa+1, the deprotonated form is 10x more concentrated than the protonated form. This transition is smooth.
-Consider the 2-amino acid group.
--The acid group typically have a pKa of ~2. Thus at pH of 3 or greater, it is always deprotonated. (at pH of 2 or slightly below it, a mixture of both deprotonated and protonated form exist)
--The amine group typically have a pKa of ~10. Thus at pH of 9 or less, it is always protonated.
--Combining the above, the zwitterion is dominant in the pH range of 3 to 9.
Consider aspartic acid, with a side group pKa of 3.6
pH=1: NH3+, COOH, Z-group COOH
pH=3: NH3+, COO-, Z-group COOH
pH=5: NH3+, COO-, Z-group COO-
pH=11: NH2, COO-, Z-group COO-
Here's what i think, please correct where incorrect:
in very acid conditions (x< 3 ) the side group, which happens to have NH2 will be effected and receive a proton
in very basic conditions, (x>9) the side group, which happens to have a COOH will be effected and donate its proton
at zwitterion, the sidegroups are not effected?
If the side group contains 1 NH2 and 1 COOH group, will the zwitterion affect the side groups? as if it does, a neutral charge is still maintained in the molecule..
Is that correct, or?
Unnecessarily complicated things, lol
FURTHERMORE
a monoprotic acid will react with a base in a 1:1 ratio, correct?
TSSM 2008 seems to say that for 1 mol of acid in a monoprotic, you need 2 mol of base...
Post by: Mao on June 09, 2011, 07:28:00 pm
Wait, at a pH of 3, why would the COOH group in the main chain donate it's proton? Shouldn't it just be the NH2 accepting protons to form NH3+?
Here's what i think, please correct where incorrect:
in very acid conditions (x< 3 ) the side group, which happens to have NH2 will be effected and receive a proton
in very basic conditions, (x>9) the side group, which happens to have a COOH will be effected and donate its proton
at zwitterion, the sidegroups are not effected?
If the side group contains 1 NH2 and 1 COOH group, will the zwitterion affect the side groups? as if it does, a neutral charge is still maintained in the molecule..
For aspartic acid, the COOH on its side group does not have the same reactivity as the COOH in its main chain group. The main chain is usually a bit more reactive. This is why at pH~3, the main chain COOH is deprotonated, and the side group is protonated.
You can think of weak acids (-COOH) and weak bases (-NH2) as 'buffers', i.e. they would like to maintain a certain pH range (i.e. pKa +/- 1). e.g. for main group -COOH, it has pKa~2. This means if pH>2, -COOH will deprotonate to lower pH. If pH<2, -COO(-) will protonate to increase pH.
I'm not too sure what you mean by 'at zwitterion, side groups are not affected'. All groups are similarly affected by their surrounding environment (see above, also thushan's post), the difference is that the groups have different 'turning points'. main chain COOH has pKa~2, main chain amine has pKa~9.
The reason why I'm throwing pKa everywhere is because it is a useful tool for working out what has protonated and deprotonated. Given the surrounding environment, we simply need to compare the pKa of the groups to see what form it is. I'll dig out the pKa for all the acidic and basic amino acids, you can use these to practice.
There are only two basic amino acids: lysine (side chain pKa = 10.3) and arginine (side chain pKa=13.2). There are only two acidic amino acids: aspartic acid (side chain pKa=3.6) and glutamic acid (side chain pKa=4.3).
Note that having an N does not make a side group basic (glutamine, asparagine and tryptophan are not basic, they do not protonate). Proline is a special case, the cyclic structure makes the main group amine more basic (pKa=10.6). Tyrosine is also a special case, the aromatic alkanol can deprotonate at high pH (pKa=10.1).
Post by: scocliffe09 on June 09, 2011, 07:46:13 pm
Would anyone be able to explain the concept of n-1 in sulfide links?If you have 500 links then you have 500 water molecules... one water is given off for every peptide bond formed.
I understand that if we have eg. 500 links, then we'd multiply that by the molar mass, and then minus 499 from M of Water, but i'm wondering if that's all.
Also, they tested on last year's exam, the idea that if you have two chains with a total of 500 peptides, there will be only 498 links, and therefore only 498 molecules of water.
Post by: taqi on June 09, 2011, 10:36:45 pm
Post by: Water on June 09, 2011, 10:38:26 pm
Post by: dmanz on June 09, 2011, 11:45:11 pm
Post by: tony3272 on June 09, 2011, 11:48:20 pm
Post by: dmanz on June 10, 2011, 12:00:13 am
You technically need to know it, but they say as long as there is only one structure which can be drawn from the systematic name you provide, then it is correct.
so what is it then? just another way of naming something?
what do you mean when you say only one structure can be drawn? what about isomers?
Post by: tony3272 on June 10, 2011, 12:06:31 am
It's basically the recognized system for naming organic compounds. What i meant by only one structure, is that if you have something such as C4H8Cl2 and you are shown the structure, you must name it so that only the given structure can be drawn, not any isomers.You technically need to know it, but they say as long as there is only one structure which can be drawn from the systematic name you provide, then it is correct.
so what is it then? just another way of naming something?
what do you mean when you say only one structure can be drawn? what about isomers?
Post by: Dr.Lecter on June 10, 2011, 03:28:08 am
Post by: thatricksta on June 10, 2011, 07:36:37 am
do examiners care if you don't do 3D representations of structural formulae? are you in contravention of losing marks if you don't? (I'm clueless with 3D representations - I just make patterns because they are cool)
You will get full marks if you draw your molecules at right angles and the bonds are to the right atoms.
Post by: mickeymouse on June 10, 2011, 02:28:39 pm
2) reacting a diprotic acid with a base would the ratio be 1 acid: 3 base?
Post by: vea on June 10, 2011, 02:38:22 pm
1) do alkanes have a higher boiling temperature than chloroalkanes? would increased branching result in a higher boiling temperature?
2) reacting a diprotic acid with a base would the ratio be 1 acid: 3 base?
1. Chloroalkanes have a higher boiling temperature than their respective alkane because the chlorine makes the molecule polar and so requires higher temperature to break the dipole-dipoles that may form. Increased branching results in a higher boiling point. I think this is because the branches start make dispersion forces with each other? Someone correct me if I'm wrong.
2. A diprotic acid has 2 protons to donate so you would need two bases (assuming it is a monoprotic base) to make up for it. The ratio is 1 acid: 2 base.
Question: A titration is performed to determine the concentration of a methanoic acid solution. Sodium hydroxide is used as the base. A suitable indicator to use for this titration would be?
Where do we have to assume the acid and the base are? Which is in the burette and which is in the conical flask and why? :S
Post by: mickeymouse on June 10, 2011, 02:47:01 pm
hope that helps...
Post by: DisaFear on June 10, 2011, 02:48:18 pm
0.308g of an ester is reacted under reflux with 20ml of 1M of NaOH solution
What is a reflux?
Post by: thushan on June 10, 2011, 02:51:42 pm
ALSO: This is an important point, but for organic chem where they ask you to draw structural formulas, NEVER use line drawings, even if they don't ask you to show all bonds, because there is a VERY HIGH chance you will be penalised. VCAA deems it too inaccurate (as line drawings don't show that you know that each carbon is bonded to 4 things).
Post by: thushan on June 10, 2011, 02:53:20 pm
Reflux is where you need to heat a liquid to boiling point but you don't want it to evaporate, so we stick in a condenser which essentially prevents any reagent being lost as vapour.
It doesn't change the nature of the question though, so don't worry about it :D
Post by: nacho on June 10, 2011, 03:12:19 pm
I've just lost a heap of confidence..
@vea - in that kind of question it doesn't matter which reagent is in the burette or pipette as either way we would produce a colour change at endpoint, given we used a suitable indicator.
ALSO: This is an important point, but for organic chem where they ask you to draw structural formulas, NEVER use line drawings, even if they don't ask you to show all bonds, because there is a VERY HIGH chance you will be penalised. VCAA deems it too inaccurate (as line drawings don't show that you know that each carbon is bonded to 4 things).
do you mean not to draw at 90 degree angles?
eg. H H
| |
H - C - C - H
| |
H H
Oh wait i think i know what you mean
you mean where you dont show the carbons/other atoms involved
Post by: mickeymouse on June 10, 2011, 03:12:58 pm
Post by: jane1234 on June 10, 2011, 03:31:53 pm
Or are both acceptable?
Post by: thushan on June 10, 2011, 03:49:49 pm
http://www.csupomona.edu/~lsstarkey/linedraw/line_images/hex_line.gif
Post by: thushan on June 10, 2011, 03:51:11 pm
Does VCAA like you to write H2CO3 or separate it into H2O and CO2 (for chemical equations - e.g. Na2CO3 + H2SO4)?
Or are both acceptable?
For an acid-base reaction don't write H2CO3 as a product. It is true that H2CO3 is formed, but it immediately decomposes (H2CO3 is unstable) to form CO2 + H2O. So write CO2 + H2O.
Post by: Dr.Lecter on June 10, 2011, 03:52:35 pm
Line drawing - something like this:
http://www.csupomona.edu/~lsstarkey/linedraw/line_images/hex_line.gif
This particularly pertains to drawing the benzene ring.
Post by: jorrrdan on June 10, 2011, 04:55:01 pm
Post by: DisaFear on June 10, 2011, 05:45:07 pm
Aspartic acid, histidine, lysine or methionine
What are we meant to look for to determine the answer?
Post by: Water on June 10, 2011, 05:45:40 pm
Post by: Tashi on June 10, 2011, 06:40:35 pm
Does VCAA like you to write H2CO3 or separate it into H2O and CO2 (for chemical equations - e.g. Na2CO3 + H2SO4)?
Or are both acceptable?
For an acid-base reaction don't write H2CO3 as a product. It is true that H2CO3 is formed, but it immediately decomposes (H2CO3 is unstable) to form CO2 + H2O. So write CO2 + H2O.
Argh I was just reading through this thread and then realised I recognised your name from someone's facebook status I'd just read in my news feed ahahaha :p
Post by: Andiio on June 10, 2011, 06:46:38 pm
Post by: generalkorn12 on June 10, 2011, 06:50:25 pm
Post by: Tashi on June 10, 2011, 06:51:51 pm
Is it better to write glycosidic linkage or an ether bond when identifying the func group linking 2 glucose molecules together?
Is it an ether bond or ether functional group?
Post by: thushan on June 10, 2011, 06:55:24 pm
Post by: thushan on June 10, 2011, 07:02:34 pm
Post by: Andiio on June 10, 2011, 07:03:36 pm
And is it worth the 'risk' to specify condensation elimination/polymerisation rather than simply condensation?
EDIT: Also, just for clarification, on an amino acid, is the -NH2 group referred to as an amine group or amino? (or both?)
Post by: luken93 on June 10, 2011, 07:06:29 pm
Do we need to know about every part of all the instruments of AAS, UV-vis, IR and NMR? Like the monochromators, the coil, the magnet, hollow cathode lamp and all?Urgh, I hope not. They're too hard to define!
btw, on that topic, what are the "official" names of the lamps in AAS and UV-Vis.
Saying "Copper Lamp" sounds way too informal haha
Post by: stonecold on June 10, 2011, 07:06:42 pm
Similarly is it better to refer to the production of an ester as esterification or condensation?
And is it worth the 'risk' to specify condensation elimination/polymerisation rather than simply condensation?
esterification is the most specific term if you are producing an ester. put condensation as well, it is not wrong.
similarly, as long as it actually is polymerisation, (i.e. grycerol + fatty acids is NOT polymerisation) then there is nothing wrong with that.
Post by: luken93 on June 10, 2011, 07:08:47 pm
Similarly is it better to refer to the production of an ester as esterification or condensation?They usually always accept either, however I wonder if you'd be penalised if you wrote both when they're both correct?
And is it worth the 'risk' to specify condensation elimination/polymerisation rather than simply condensation?
I could just imagine myself sitting there at 1hr 29mins continuously rewriting the name of a linkage hoping that I choose the write one...
Also, linkage or bond? Or is it case specific...
Post by: thushan on June 10, 2011, 07:10:50 pm
Post by: Dr.Lecter on June 10, 2011, 07:11:48 pm
Do we need to know about every part of all the instruments of AAS, UV-vis, IR and NMR? Like the monochromators, the coil, the magnet, hollow cathode lamp and all?
basic knowledge of AAS and UV-vis - NMR is far too complex at this point in time
Post by: Tashi on June 10, 2011, 07:16:10 pm
Do we need to know about every part of all the instruments of AAS, UV-vis, IR and NMR? Like the monochromators, the coil, the magnet, hollow cathode lamp and all?
I reckon you'd have to know about the lamp and what it does. Also probably the monochromator but that's not too hard. I don't think you'd really have to know the fine details of NMR (like the radio transmitter coils or whatever), however I'm not sure.
Post by: Andiio on June 10, 2011, 07:17:42 pm
Similarly is it better to refer to the production of an ester as esterification or condensation?
And is it worth the 'risk' to specify condensation elimination/polymerisation rather than simply condensation?
esterification is the most specific term if you are producing an ester. put condensation as well, it is not wrong.
similarly, as long as it actually is polymerisation, (i.e. grycerol + fatty acids is NOT polymerisation) then there is nothing wrong with that.
In the exam are we allowed to write answers like this: esterification/condensation reaction.
:\
Post by: stonecold on June 10, 2011, 07:20:33 pm
Similarly is it better to refer to the production of an ester as esterification or condensation?
And is it worth the 'risk' to specify condensation elimination/polymerisation rather than simply condensation?
esterification is the most specific term if you are producing an ester. put condensation as well, it is not wrong.
similarly, as long as it actually is polymerisation, (i.e. grycerol + fatty acids is NOT polymerisation) then there is nothing wrong with that.
In the exam are we allowed to write answers like this: esterification/condensation reaction.
:\
As long as they are both right, I can't see why not. I frequently do it because generally there is more than one term to describe what is going on.
Post by: mickeymouse on June 10, 2011, 07:40:03 pm
Post by: Tashi on June 10, 2011, 07:49:53 pm
would we have to know how to draw the reactions of specific addition polymerisation reactions? e.g. PVC and polystyrene
I think they'd give you the structure of the monomer/polymer first if they expected you to draw the reaction.
Post by: luken93 on June 10, 2011, 08:03:24 pm
Post by: nacho on June 10, 2011, 09:27:05 pm
my answer - Biodiesel is a fuel, and if it were to combust in the presence of a high concentration of water, the water would prevent the combustion from occurring.
Neap answer: The biodiesel must be of a high enough concentration to burn in the combustion process.
am i correct to some degree?
Post by: DisaFear on June 10, 2011, 09:37:10 pm
I faced that question yesterday, didn't know the answer so I wrote "Water is not a fuel so may hinder performance" :P heh
Post by: Water on June 10, 2011, 09:43:15 pm
But its to remove all impurities of biodiesel to obtain its most concentrated form.
Was using it based on Ethanol, and its process of obtaining it ;x
Post by: nacho on June 10, 2011, 09:44:50 pm
i lost like 3 marks cause i put the wrong things in my calc lmao
Post by: DisaFear on June 10, 2011, 09:47:14 pm
I'll just say I lost ~10 marks in the short answer
My scores are steadily improving though
Post by: Vincezor on June 10, 2011, 09:51:04 pm
whatd you guys get on neap 11?
i lost like 3 marks cause i put the wrong things in my calc lmao
Wow what a beast! I lost 6 marks (damn WVO!) but I discussed some of the corrections with my teacher and she said 2 of the questions I marked wrong were right. But who cares, I'll just keep the lower score haha :laugh:
Post by: Andiio on June 10, 2011, 09:53:00 pm
Post by: nacho on June 10, 2011, 09:54:30 pm
haha no i meantwhatd you guys get on neap 11?
i lost like 3 marks cause i put the wrong things in my calc lmao
Wow what a beast! I lost 6 marks (damn WVO!) but I discussed some of the corrections with my teacher and she said 2 of the questions I marked wrong were right. But who cares, I'll just keep the lower score haha :laugh:
"I lost 3 marks, just from the calculator mistakes"
many more marks were followed by those LOL.
I lost 13 overall,
could have/should have been 9, as i went back and 'fixed' up one of my answers only to put the wrong answer and lose 4 marks for the entire second-half :(
edit: damn 6, marks is quite pro. How many exams have you done? Hopefully it was one of your later exams..!
I like neap papers, they are challenging
Post by: Dr.Lecter on June 10, 2011, 09:55:03 pm
Explain why it is necessary to remove water and other contaminants from the biodiesel.fyi - water is not very good for older type diesel engines so to some extent, you can justify yourself by saying contaminated biodiesel defeats the purpose of being efficient ( it is not good for engines as it can cause injector nozzle and pump corrosion)
my answer - Biodiesel is a fuel, and if it were to combust in the presence of a high concentration of water, the water would prevent the combustion from occurring.
Neap answer: The biodiesel must be of a high enough concentration to burn in the combustion process.
am i correct to some degree?
Post by: luken93 on June 10, 2011, 10:02:34 pm
What did everyone find was the hardest '11 exam?I think Lisachem was probably the biggest step up, havent done TSFX/TSSM though..
Post by: jane1234 on June 10, 2011, 10:16:07 pm
Post by: thushan on June 10, 2011, 10:19:07 pm
What did everyone find was the hardest '11 exam?I think Lisachem was probably the biggest step up, havent done TSFX/TSSM though..
Agreed. That was a good, hard paper. Shame I'm still making careless mistakes :S
Post by: nacho on June 10, 2011, 10:19:57 pm
:o I just did KBT 2010 and now I'm freaked out I'm going to fail... are they supposed to be excessively hard!!??yea, they tried to make it really hard.
Post by: jane1234 on June 10, 2011, 10:23:29 pm
:o I just did KBT 2010 and now I'm freaked out I'm going to fail... are they supposed to be excessively hard!!??yea, they tried to make it really hard.
*sigh of relief*
Thank you, I was getting all paranoid because I didn't know what the hell a "chemical marker" did to fuels :idiot2:
Post by: Vincezor on June 10, 2011, 10:37:46 pm
:o I just did KBT 2010 and now I'm freaked out I'm going to fail... are they supposed to be excessively hard!!??
Man that was one hell of an exam. The last page where you had to draw the nucleotides... I just couldn't be bothered for only 3 marks :/ I think I lost around ~20 marks overall, not very happy. I wish more exams were hard like this, this and only a few others really made me doubt my ability for chem whilst the others are confidence boosters I guess.
@nacho, yes it was one of my later of exams (I think one of the last five) so don't be worried! :P
Post by: chemkid_23 on June 10, 2011, 10:38:38 pm
It goes that a volume of 180ml of 1.0M of HCl is added to 100mL of 1.0M of NaOh; find the pH of the resultant solution.
Well I've worked it out, and keep getting it wrong. The solutions say that c(HCl)= 0.080/0.250 and not 0.080/0.280 which is hwat i did. Where does the 250 ml come from; solutions say it is 150ml + 100ml; where is the 150 coming from? Please help
Post by: Lols123 on June 10, 2011, 10:40:46 pm
I just did that one
It almost made me depressed until I read this thread xD
how did you go on it? ^^
Post by: acinod on June 10, 2011, 11:03:31 pm
LisaChem 2010 was also pretty hard along with 2009 and 2010 TSFX, 2010 NEAP and 2011 CSE.
Insight is challenging but is actually all relavant so they are the best I think.
Post by: Water on June 10, 2011, 11:05:56 pm
Post by: DisaFear on June 10, 2011, 11:07:58 pm
Post by: taiga on June 10, 2011, 11:08:29 pm
Post by: mickeymouse on June 10, 2011, 11:10:40 pm
Post by: DisaFear on June 10, 2011, 11:20:30 pm
(http://i244.photobucket.com/albums/gg17/xPloSiV01/DN.jpg)
What's wrong with it? Or do you mean in a reaction?
Post by: jane1234 on June 11, 2011, 12:17:08 am
LOL Jane
I just did that one
It almost made me depressed until I read this thread xD
how did you go on it? ^^
Haha lost about 15 marks :( So around 80%
I like the confidence-booster ones better :D
Post by: luken93 on June 11, 2011, 09:26:11 am
Also, should we provide catalysts wherever possible in a reaction?
Post by: SDPHD on June 11, 2011, 09:34:03 am
What is the molar mass of this?
(http://i.imgur.com/GPD3a.png)
More specifically, what is the name and molar mass of this?
(http://i.imgur.com/7ZPd7.png)
I cant get this question right because my molar mass is off.
Post by: mickeymouse on June 11, 2011, 09:45:49 am
This? (page 205)
(http://i244.photobucket.com/albums/gg17/xPloSiV01/DN.jpg)
What's wrong with it? Or do you mean in a reaction?
yup that one but after a reaction with another nucleotide the H disappears on page 206?
edit: I think I get it now there is no need to draw the other hydrogens anymore since it's still present by just drawing the ring
Post by: luken93 on June 11, 2011, 09:56:52 am
Okay, this is quite an idiotic question, sorry.Okay, so the molar mass of benzene is C6H6 = 78g/mol
What is the molar mass of this?
(http://i.imgur.com/GPD3a.png)
More specifically, what is the name and molar mass of this?
(http://i.imgur.com/7ZPd7.png)
I cant get this question right because my molar mass is off.
However, for every bond that it makes with someone else, the Hydrogen is lost. So, for the diagram above, there are two bonds to benzene, hence it would become C6H4.
I'm assuming this is where you went wrong, let me know if you still can't get it :)
Post by: SDPHD on June 11, 2011, 10:06:14 am
Okay, so the molar mass of benzene is C6H6 = 78g/mol
However, for every bond that it makes with someone else, the Hydrogen is lost. So, for the diagram above, there are two bonds to benzene, hence it would become C6H4.
I'm assuming this is where you went wrong, let me know if you still can't get it :)
Oh right!
I get it now, thanks!
Post by: homosapiens on June 11, 2011, 10:24:20 am
alkenes, alkanes, ether, ester, amine, carboxylic acids, alcohols, amide?
And if so, why are alkenes less polar than alkanes...
Post by: luken93 on June 11, 2011, 10:28:55 am
Post by: mickeymouse on June 11, 2011, 10:36:20 am
I thought there were 2 environments but the answer says 3?
Post by: homosapiens on June 11, 2011, 10:37:47 am
Phosphates in the data book, why do some exams say it contains OH while the data book shows O-?
Not entirely sure, so someone please correct me if I'm wrong, but phosphate groups usually have OH but once bonded to form a nucleotide, they become O-, that's why DNA molecules are negatively charged
Post by: mickeymouse on June 11, 2011, 10:38:49 am
Post by: pi on June 11, 2011, 10:51:45 am
Disulfide Link/Bridge - Both ok?
Also, should we provide catalysts wherever possible in a reaction?
Both are fine, I usually go with disulfide link though
I try to, but if I forget, I just write 'catalyst'. Had a lecture (MHS + MacRob) with the chief examiner, and he doesn't expect knowledge of all catalysts (including ones like Ni, etc.). Main ones are H2SO4 and UV light from what I understood of him.
Post by: eeps on June 11, 2011, 10:57:27 am
how many H environments in this molecule? CH3(CH2)3CH3
I thought there were 2 environments but the answer says 3?
(http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/pentane.gif)
I believe it's 3. The 2 CH3's at the ends makes one hydrogen environment. The 2 CH2's which are attached to the CH3's count as another hydrogen environment. The CH2 in the middle is another environment. In total, there is 3.
Post by: mickeymouse on June 11, 2011, 11:04:53 am
how do we attach scanned images? I have another question too long to explain...
Post by: pi on June 11, 2011, 11:06:10 am
-> Scroll down to 'Additional Options'
-> Click
-> See 'Attach', click 'Choose file' button
Quote
Allowed file types: doc, gif, jpg, mpg, pdf, png, txt, zip, tar
Maximum attachment size allowed: 2048 KB, per post: 4
Post by: pi on June 11, 2011, 11:16:25 am
Phosphates in the data book, why do some exams say it contains OH while the data book shows O-?
I'd like to know this too! Not sure and different diagrams do different things. I THINK, that when it is in DNA, there is a O- (hence net negative charge of DNA molecule) and a =O coming from the P, with the other two Os being in phosphodiester bonds. Not 100% sure on this though.
EDIT: didn't see answer by homosapiens and mickeymouse, my bad
Is the order of polarity for organic molecules from least polar to most polar:least polar -> most polar
alkenes, alkanes, ether, ester, amine, carboxylic acids, alcohols, amide?
And if so, why are alkenes less polar than alkanes...
alkenes, alkanes, amine, alkanol (note, O has a higher electronegativity than N), carboxylic acid. Not sure on 'ester, ether, halogen and amide', but they are between alkanes and amines, never seen those ones examined though.
Alkenes are as polar as alkanes, but have lower boiling points because there are less hydrogens, and hence, less net dispersion forces between alkene molecules.
Post by: homosapiens on June 11, 2011, 11:20:11 am
Also about the phosphate group thing, I'm pretty sure the data book presents the phosphate group as if it's bonded to the deoxyribose sugar (ie it loses its hydrogens once it's bonded)
Moderator action: removed real name, sorry for the inconvenience
Post by: pi on June 11, 2011, 11:22:41 am
Thanks pi for clearing that up!
Also about the phosphate group thing, I'm pretty sure the data book presents the phosphate group as if it's bonded to the deoxyribose sugar (ie it loses its hydrogens once it's bonded)
Yep, I think your right.
So, am I right in saying that when it isn't bonded to a nucleotide and sugar, it has 3 OH groups? Does that mean that the phosphate at the end of the DNA chain will still have an -OH group attached to the phosphate?
Moderator action: removed real name, sorry for the inconvenience
Post by: mickeymouse on June 11, 2011, 11:24:36 am
if it was a monoprotic acid wouldn't the mole of the acid be the same as that of the base?
btw thanks pi
Moderator action: removed real name, sorry for the inconvenience
Post by: pi on June 11, 2011, 11:29:09 am
this is a solution to a question, pretty much an acid and base are titrated and 17.8mL of an unknown acid is used.
if it was a monoprotic acid wouldn't the mole of the acid be the same as that of the base?
btw thanks pi
If you write up an equation, lets see. eg. HCl
2HCl + Na2CO3 --> 2NaCl + H2O + CO2
There are 2 mol of monoprotic acid needed, as there are two mol of Na in the base. Hence, mol is double for the monoprotic. If we use H2SO4, we see that mole ratio is 1:1, etc for a triprotic acid (try phosphoric acid for example)
Moderator action: removed real name, sorry for the inconvenience
Post by: Asx4Life on June 11, 2011, 11:44:40 am
b)For each environment, how many splits will they produce?
2a)For CH3CH2CH2CH3 how many H environments are there?
b)For each environment, how many splits will they produce?
3)What is the ratio of areas under peaks for propane? I thought it was 3:2:3. But answer says 3:1
For 2chloropropane, I thought it was 3:1:3, but answer says 6:1 do we need to add the Hydrogens that are in equivalent environments?
4)Take propanol as an example. What is the group of atoms that produces triplet?
5)What does peak height and peak area represent in HPLC/GC. Is is the same?
Just need some help on NMR where I'm weak at. Thanks VN!! =)
Post by: pi on June 11, 2011, 11:56:44 am
1a)For CH3CH2CH2CH2CH3 how many H environments are there?
b)For each environment, how many splits will they produce?
2a)For CH3CH2CH2CH3 how many H environments are there?
b)For each environment, how many splits will they produce?
3)What is the ratio of areas under peaks for propane? I thought it was 3:2:3. But answer says 3:1
For 2chloropropane, I thought it was 3:1:3, but answer says 6:1 do we need to add the Hydrogens that are in equivalent environments?
4)Take propanol as an example. What is the group of atoms that produces triplet?
5)What does peak height and peak area represent in HPLC/GC. Is is the same?
Just need some help on NMR where I'm weak at. Thanks VN!! =)
1. a) 3 different H environments (note the symmetry)
b) 3 peak sets: triplet, 'pentet', 'hexet' (you know what I mean :P)
2. a) 2 different H environments (note the symmetry)
b) 2 peak sets: triplet, 'hexet'
Note: I'm not taking into account multiplicity, and hence, could be wrong here
3. a) Propane has only two different H environments. 6 H : 2 H = 3:1
b) 2-chloropropane has 2 different H environments. 6 H : 1 H = 6:1. Yep, you need to add.
4. Assuming primary alkanol (ie propan-1-ol). The reading will be from either the CH3- at the end or the bolded hydrogen in -CH2-(OH). This is because the adjacent carbon to each group had 2 H (in -CH2-), hence a split of 3 peaks (just take it as the 'n+1 rule', but there is a more complicated reason based on nucleus spins and those combinations)
5. Not sure on peak height, but I don't think it means anything except that if there is a peak, there is a Rt for a specific component. The area gives the relative amount.
Post by: DavidSheena on June 11, 2011, 12:14:59 pm
And with sig figs: If there is a question with 4 parts and the first part which is the explanation has two sig figs. And then the 4th part has 4 sig figs (granted no calculations or values from the information provided in the explanation is used). Would two sig figs be sufficient or would it be four?
The answers said 4 I put 2 :S
Post by: pi on June 11, 2011, 12:17:15 pm
I guess this is a trivial question but If i get exactly the same answer as required and show different working do I still get awarded full marks?
As long as its fairly logical, it should be fine :)
Post by: nacho on June 11, 2011, 12:23:05 pm
Post by: DavidSheena on June 11, 2011, 12:25:00 pm
Post by: Asx4Life on June 11, 2011, 12:30:32 pm
For question 2, I originally thought the same thing as you, but the answer is actually 2 singlets, because the molecule is symmetrical on both sides. Can anyone confirm this?1a)For CH3CH2CH2CH2CH3 how many H environments are there?
b)For each environment, how many splits will they produce?
2a)For CH3CH2CH2CH3 how many H environments are there?
b)For each environment, how many splits will they produce?
3)What is the ratio of areas under peaks for propane? I thought it was 3:2:3. But answer says 3:1
For 2chloropropane, I thought it was 3:1:3, but answer says 6:1 do we need to add the Hydrogens that are in equivalent environments?
4)Take propanol as an example. What is the group of atoms that produces triplet?
5)What does peak height and peak area represent in HPLC/GC. Is is the same?
Just need some help on NMR where I'm weak at. Thanks VN!! =)
1. a) 3 different H environments (note the symmetry)
b) 3 peak sets: triplet, 'pentet', 'hexet' (you know what I mean :P)
2. a) 2 different H environments (note the symmetry)
b) 2 peak sets: triplet, 'hexet'
Note: I'm not taking into account multiplicity, and hence, could be wrong here
3. a) Propane has only two different H environments. 6 H : 2 H = 3:1
b) 2-chloropropane has 2 different H environments. 6 H : 1 H = 6:1. Yep, you need to add.
4. Assuming primary alkanol (ie propan-1-ol). The reading will be from either the CH3- at the end or the bolded hydrogen in -CH2-(OH). This is because the adjacent carbon to each group had 2 H (in -CH2-), hence a split of 3 peaks (just take it as the 'n+1 rule', but there is a more complicated reason based on nucleus spins and those combinations)
5. Not sure on peak height, but I don't think it means anything except that if there is a peak, there is a Rt for a specific component. The area gives the relative amount.
Thanks for the clarity on question 3.
Question 4 is the problem, the splitting of the environment CH3 causes a triplet. But the group of atoms that actually causes a triplet is the neighbouring carbon atom of CH2. Can anyone clarify this?
I thought area means concentration and height means amount?
Moderator action: removed real name, sorry for the inconvenience
Post by: Greatness on June 11, 2011, 12:32:43 pm
Post by: Greatness on June 11, 2011, 12:34:35 pm
Thank you. And also engage said that the bonding between deoxyribose and phosphate is hydrogen bonding. Is that correct? Or is it covalent?Yeah it's covalent, more specifically phsphodiester.
Post by: nacho on June 11, 2011, 12:38:40 pm
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'
Post by: Greatness on June 11, 2011, 12:44:39 pm
do we need to know PCR?Yes we have to know that. I dont think we need to know the specifics but all you have to know is that you chuck some DNA samples (or amino acids) into the negative side of the machine, bigger molecules i.e. the ones with higher molar masses move less, smaller molecules move further, negative molecules move further as they are attracted to the positive side of the gel/machine thing and positive ones move less.
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'
Dna profile is pretty much what the samples look like after they have been run in the machine. So you will get different bands at different places of the gel. From here you can match the bands with someone elses and determine who the criminal is etc.
Post by: vea on June 11, 2011, 01:18:15 pm
Post by: scocliffe09 on June 11, 2011, 01:26:24 pm
That's not actually PCR - you described gel electrophoresis. And I think an awareness of both techniques is useful.do we need to know PCR?Yes we have to know that. I dont think we need to know the specifics but all you have to know is that you chuck some DNA samples (or amino acids) into the negative side of the machine, bigger molecules i.e. the ones with higher molar masses move less, smaller molecules move further, negative molecules move further as they are attracted to the positive side of the gel/machine thing and positive ones move less.
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'
Dna profile is pretty much what the samples look like after they have been run in the machine. So you will get different bands at different places of the gel. From here you can match the bands with someone elses and determine who the criminal is etc.
PCR - DNA replication in a machine.
Electrophoresis - run chopped up fragments of DNA through a porous gel. Be able to label terminals, and remember shorter fragments move further.
Post by: nacho on June 11, 2011, 01:28:59 pm
http://www.youtube.com/watch?v=x5yPkxCLads
damn im so unsure about the exam..hopefully it is a neap style exam
Post by: Greatness on June 11, 2011, 01:42:51 pm
Hahahah yeah i did too.... whoops this is what kills me in the exams :/That's not actually PCR - you described gel electrophoresis. And I think an awareness of both techniques is useful.do we need to know PCR?Yes we have to know that. I dont think we need to know the specifics but all you have to know is that you chuck some DNA samples (or amino acids) into the negative side of the machine, bigger molecules i.e. the ones with higher molar masses move less, smaller molecules move further, negative molecules move further as they are attracted to the positive side of the gel/machine thing and positive ones move less.
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'
Dna profile is pretty much what the samples look like after they have been run in the machine. So you will get different bands at different places of the gel. From here you can match the bands with someone elses and determine who the criminal is etc.
PCR - DNA replication in a machine.
Electrophoresis - run chopped up fragments of DNA through a porous gel. Be able to label terminals, and remember shorter fragments move further.
Have VCAA tested this much in the past few years? Because from a fwe of the exams ive done they usually incorporate all of PCR, gel electrophoresis, sometimes restriction enzymes into one big SA question.
Post by: scocliffe09 on June 11, 2011, 02:18:32 pm
Yes - you're exactly right about the SAQ - they're more interested in you understanding that we exploit some of DNA's properties to analyse it (universality, redundancy, negative charge, fragmentation following cleavage by restriction enzymes).
Hahahah yeah i did too.... whoops this is what kills me in the exams :/
Have VCAA tested this much in the past few years? Because from a fwe of the exams ive done they usually incorporate all of PCR, gel electrophoresis, sometimes restriction enzymes into one big SA question.
Post by: mickeymouse on June 11, 2011, 02:23:42 pm
Post by: pi on June 11, 2011, 02:42:06 pm
1. Am I right in saying that when a phosphate isn't bonded to a nucleotide and sugar, it has 3 OH groups? Does that mean that the phosphate at the end of the DNA chain will still have an -OH group attached to the phosphate?
Thanks a lot guys :)
Post by: tony3272 on June 11, 2011, 02:55:18 pm
Could someone give me hand with these ones please?just for Q2.
1. Am I right in saying that when a phosphate isn't bonded to a nucleotide and sugar, it has 3 OH groups? Does that mean that the phosphate at the end of the DNA chain will still have an -OH group attached to the phosphate?
2. (attached) The answer is A btw
Thanks a lot guys :)
Glycine has 1 nitrogen, whereas urea has 2. Therefore the ratio of glycine : urea is 2 : 1
If you work out the mol of glycine you get 1/75mol, which you then half and multiply by 60 to get the mass of urea.
Moderator action: removed real name, sorry for the inconvenience
Post by: pi on June 11, 2011, 02:56:55 pm
just for Q2.
Glycine has 1 nitrogen, whereas urea has 2. Therefore the ratio of glycine : urea is 2 : 1
If you work out the mol of glycine you get 1/75mol, which you then half and multiply by 60 to get the mass of urea.
Cheers :) Makes sense now!
Post by: scocliffe09 on June 11, 2011, 03:05:25 pm
Could someone give me hand with these ones please?phosphate is a derivative of phosphoric acid - so it depends entirely on the environment as to whether you have H3PO4, PO4 3- or anything in between. It is probably possible, if it were an acidic environment, to protonate the phosphate group but I don't think you need to know details.
1. Am I right in saying that when a phosphate isn't bonded to a nucleotide and sugar, it has 3 OH groups? Does that mean that the phosphate at the end of the DNA chain will still have an -OH group attached to the phosphate?2. (attached) The answer is A btwSolved now, thanks tony3272! :)
Thanks a lot guys :)
Moderator action: removed real name, sorry for the inconvenience
Post by: pi on June 11, 2011, 03:07:55 pm
What about the -OH at the ends of DNA? Is that also dependent on the environment?
Post by: The Full House on June 11, 2011, 04:37:13 pm
Post by: luken93 on June 11, 2011, 04:49:08 pm
C2H6O + C2H4O2 -> C4H8O2 + H2O or
CH3CH2OH + CH3COOH -> CH3COOCH2CH3 + H2O or
C2H5OH + CH3COOH -> CH3COOC2H5 + H2O
Thanks
Post by: jane1234 on June 11, 2011, 04:56:08 pm
If you're wanting to show the specific properties of a reaction (ie alkanol + carboxylic -> ester), can you still write it like
C2H6O + C2H4O2 -> C4H8O2 + H2O or
CH3CH2OH + CH3COOH -> CH3COOCH2CH3 + H2O or
C2H5OH + CH3COOH -> CH3COOC2H5 + H2O
Thanks
Don't think it matters unless they specifically ask for the semistructural formula or molecular formula... if they don't say I'd do them in semistructural... less likely to make silly mistakes counting carbon atoms :)
Post by: Bozo on June 11, 2011, 04:56:52 pm
Post by: cltf on June 11, 2011, 05:12:14 pm
Post by: nacho on June 11, 2011, 05:19:40 pm
do we take that into consideration when giving our answers in significant figures?
Post by: Andiio on June 11, 2011, 05:29:07 pm
Post by: nacho on June 11, 2011, 05:33:07 pm
if we are given a question telling us that a process is only 90% efficient, and that masses of 9.000 kg etc are produced, do we take into account the 2 sig figs of the 90%?i think it'd be the weight
something to 1 sig fig seems off (wait is 90% 1 or 2 sig figs?)
Post by: mickeymouse on June 11, 2011, 05:34:37 pm
Post by: Andiio on June 11, 2011, 06:14:48 pm
Post by: Vincezor on June 11, 2011, 06:23:55 pm
Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\
Argh that's from Engage right? I wasn't sure of the answer for part b) either. How would you even work it out? :S
Post by: DisaFear on June 11, 2011, 06:24:48 pm
I'm stupid so I just think it's 2:1, amirite?
Or is it 1:2? The reactant has 2 moles of P, the other dude has 4
Post by: Andiio on June 11, 2011, 06:25:27 pm
Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\
Argh that's from Engage right? I wasn't sure of the answer for part b) either. How would you even work it out? :S
Yeah it is, I was like 'WTF' at the question. The solutions don't even make sense, they state that C is the limiting reagent when it had the greatest amount of mol ==
For the question: Name the type of bonding that is present between a deoxyribose molecule and phosphate molecule,
I wrote phosphodiester bonding - the answers stated hydrogen bonding. Am I right or is it actually H-bonding?
Thanks!
Post by: mickeymouse on June 11, 2011, 06:32:09 pm
it was worded weirdly so don't worry about it... so dodgy!
Post by: scocliffe09 on June 11, 2011, 06:34:53 pm
Nope you're definitely right - It is (if we're being picky), technically a phosphate ester bond (it's only in a nucleic acid that phosphodiester bonds are formed). But it's not H bonds.Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\
Argh that's from Engage right? I wasn't sure of the answer for part b) either. How would you even work it out? :S
Yeah it is, I was like 'WTF' at the question. The solutions don't even make sense, they state that C is the limiting reagent when it had the greatest amount of mol ==
For the question: Name the type of bonding that is present between a deoxyribose molecule and phosphate molecule,
I wrote phosphodiester bonding - the answers stated hydrogen bonding. Am I right or is it actually H-bonding?
Thanks!
Nacho - concentrations (2M) are definitely counted in sig figs. Some papers are just slack (e.g. tsfx).
Luken - all of those reactions are fine. But remember, you want the examiner to give you the marks you deserve, so make whatever the question is asking for REALLY obvious - treat the examiner like both a complete douche and a chem nut :)
JayCanteloupe - DEFINITELY know the solubility table. REALLY important.
pi - the OH at the end (I assume you mean the 3' end) is connected to a carbon, so it's much less polar than the phosphate group, so much less likely to be acidic - so it's almost always going to be an OH group.
Hope that helps everyone
Moderator action: removed real name, sorry for the inconvenience
Post by: Andiio on June 11, 2011, 06:37:18 pm
Nope you're definitely right - It is (if we're being picky), technically a phosphate ester bond (it's only in a nucleic acid that phosphodiester bonds are formed). But it's not H bonds.Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\
Argh that's from Engage right? I wasn't sure of the answer for part b) either. How would you even work it out? :S
Yeah it is, I was like 'WTF' at the question. The solutions don't even make sense, they state that C is the limiting reagent when it had the greatest amount of mol ==
For the question: Name the type of bonding that is present between a deoxyribose molecule and phosphate molecule,
I wrote phosphodiester bonding - the answers stated hydrogen bonding. Am I right or is it actually H-bonding?
Thanks!
Nacho - concentrations (2M) are definitely counted in sig figs. Some papers are just slack (e.g. tsfx).
Luken - all of those reactions are fine. But remember, you want the examiner to give you the marks you deserve, so make whatever the question is asking for REALLY obvious - treat the examiner like both a complete douche and a chem nut :)
JayCanteloupe - DEFINITELY know the solubility table. REALLY important.
pi - the OH at the end (I assume you mean the 3' end) is connected to a carbon, so it's much less polar than the phosphate group, so much less likely to be acidic - so it's almost always going to be an OH group.
Hope that helps everyone
Awesome thanks. So many errors in that paper D:
Do you think it'd be best to simply write covalent bonding in the exam if a question came up asking about the type of bonding between a deoxyribose sugar and a phosphate group?
Moderator action: removed real name, sorry for the inconvenience
Post by: nacho on June 11, 2011, 06:58:44 pm
Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\is the answer .1 mol?
can someone link me to the solutions please?
Post by: luken93 on June 11, 2011, 07:02:03 pm
So scocliffe, even though my 3rd reaction is as cltf said, "a hybrid", it can still be used? I didn't think it would be either, but if you had a fatty acid I'm not going to write out a 20 carbon chain with 3 double bonds all in semi-structural while still showing the carboxyl aspect of it...
Post by: luken93 on June 11, 2011, 07:19:35 pm
Post by: mickeymouse on June 11, 2011, 07:23:48 pm
Post by: nacho on June 11, 2011, 07:23:53 pm
i.e the instruments used/purposes and their names
also,
whats the answer to andiio's question?
is it 0.1 mol for part b) ?
Post by: taiga on June 11, 2011, 07:26:33 pm
Post by: Andiio on June 11, 2011, 07:32:36 pm
out of all the spectroscopic techniques, which ones do we need to know in detail?
i.e the instruments used/purposes and their names
also,
whats the answer to andiio's question?
is it 0.1 mol for part b) ?
Yeah it is, what was your reasoning for it though?
Post by: scocliffe09 on June 11, 2011, 07:41:17 pm
Well that is technically the "type of bonding", phosphodiester is more the name of the specific bond...As long as you are happy that you convince the examiner of what you want to convince them, then go for it! CHO and CHCOOH are both 100% acceptable forms for fatty acids. Also your oxidation question - you're right.
So scocliffe, even though my 3rd reaction is as cltf said, "a hybrid", it can still be used? I didn't think it would be either, but if you had a fatty acid I'm not going to write out a 20 carbon chain with 3 double bonds all in semi-structural while still showing the carboxyl aspect of it...
Hope UNichem went well Luken
Post by: nacho on June 11, 2011, 07:42:17 pm
I assumed there was one mol for each reactant as it says 'for every mole'
that means
1 mol of Ca... 1 mol of Si... and 1 mol of C.
Find the limiting reagent.
1 mol of Ca3(PO4)2 requires 3 mol of SiO2 and 5 mol of C
the limiting reagent is therefore Carbon
with 1 mol of carbon, 1/5 mol of Ca3(PO4)2 will react (simple stoich ratios)
and 2/5 mol of SiO2 will react (but all you dont even need to calculate both of them, you can just use the carbon figure)
Carbon : P4
10 : 1
therefore 1 mol of carbon produces .1 mol of P4
check with the others
Post by: Andiio on June 11, 2011, 07:45:18 pm
I did this:
I assumed there was one mol for each reactant as it says 'for every mole'
that means
1 mol of Ca... 1 mol of Si... and 1 mol of C.
Find the limiting reagent.
1 mol of Ca3(PO4)2 requires 3 mol of SiO2 and 5 mol of C
the limiting reagent is therefore Carbon
with 1 mol of carbon, 1/5 mol of Ca3(PO4)2 will react (simple stoich ratios)
and 2/5 mol of SiO2 will react (but all you dont even need to calculate both of them, you can just use the carbon figure)
Carbon : P4
10 : 1
therefore 1 mol of carbon produces .1 mol of P4
check with the others
Limiting reagent is carbon?
Post by: nacho on June 11, 2011, 07:49:20 pm
yea, because if you have 1 mol of each reactantI did this:
I assumed there was one mol for each reactant as it says 'for every mole'
that means
1 mol of Ca... 1 mol of Si... and 1 mol of C.
Find the limiting reagent.
1 mol of Ca3(PO4)2 requires 3 mol of SiO2 and 5 mol of C
the limiting reagent is therefore Carbon
with 1 mol of carbon, 1/5 mol of Ca3(PO4)2 will react (simple stoich ratios)
and 2/5 mol of SiO2 will react (but all you dont even need to calculate both of them, you can just use the carbon figure)
Carbon : P4
10 : 1
therefore 1 mol of carbon produces .1 mol of P4
check with the others
Limiting reagent is carbon?
and Ca3PO4 needs ten times its own amount to react, doesnt that mean that Carbon is limiting Ca3PO4 from being used up?
1 mol of Ca3PO4 needs 10 mol of carbon, yet there is only 1 mol present
Post by: jane1234 on June 11, 2011, 07:53:23 pm
If a question says that aspirin was hydrolysed in alkaline conditions... and asks you to draw salicylic acid wouldn't you draw it as -COO- instead of -COOH... or just leave it as the -COOH even though it would lose a proton in basic conditions? ???
Post by: luken93 on June 11, 2011, 08:03:53 pm
Cheers. Yeah, it wasn't too bad - but the completely revamped the format of the previous years which wasn't good :(Well that is technically the "type of bonding", phosphodiester is more the name of the specific bond...As long as you are happy that you convince the examiner of what you want to convince them, then go for it! CHO and CHCOOH are both 100% acceptable forms for fatty acids. Also your oxidation question - you're right.
So scocliffe, even though my 3rd reaction is as cltf said, "a hybrid", it can still be used? I didn't think it would be either, but if you had a fatty acid I'm not going to write out a 20 carbon chain with 3 double bonds all in semi-structural while still showing the carboxyl aspect of it...
Hope UNichem went well Luken
Ah well, I'd rather do better in normal chem :P
Post by: Water on June 11, 2011, 09:11:44 pm
In atomic Absorption Spectroscopy (AAS) the analysis is based on the
A) Absorption by the analyte of visible light only.
B) Absorption by the analyte of visible and UV light
C) Absorption of the emissions by the analyte in the instrument
D) Absorption of the atoms of the analyte by the standard solution.
Your Answer and Your Reason Why. Your reason must a 2 mark worth answer. Thankyou
Post by: mickeymouse on June 11, 2011, 09:28:08 pm
also how would you write out the semi-structural formula for aspirin especially with the branching?
Post by: scocliffe09 on June 11, 2011, 10:03:11 pm
TSFX..B is correct. AAS can use the UV and visible spectra to measure absorption. In these spectra, electrons absorb light and move to higher energy states
In atomic Absorption Spectroscopy (AAS) the analysis is based on the
A) Absorption by the analyte of visible light only.
B) Absorption by the analyte of visible and UV light
C) Absorption of the emissions by the analyte in the instrument
D) Absorption of the atoms of the analyte by the standard solution.
Your Answer and Your Reason Why. Your reason must a 2 mark worth answer. Thankyou
D - we're not measuring how many atoms are absorbed, we're measuring light.
C - It's not AES - we measure absorbance because this is proportional to conc.
A - AAS can do UV as well as visible. depends entirely on the metal and wavelength we choose
Post by: Mao on June 12, 2011, 12:45:58 am
In AAS, the analyte emission spectra (from hollow cathode lamp) is shown at the analyte, which absorbs the radiation. Thus we are measuring the absorption of the emission spectra. This emission spectra is not emitted by the analyte in sample, but it is emitted by standardized analyte in the cathode lamp.
One thing to stress is that AAS is know for discrete emission lines. I think it is incomplete to say it measures absorption of visible and UV light, which can mean a continuous spectrum is being generated at the source.
In AES, we are not measuring absorption, we are measuring the amount of emission.
Post by: scocliffe09 on June 12, 2011, 12:53:17 am
I believe the answer is C.I think that disagrees with the definition of analyte though. Analyte is specifically the thing you are measuring - in this case the concentration of. I agree that neither B nor A is a perfect answer either, because, as you say, you are measuring discrete wavelengths, probably only one, in which case UV and visible light are not both used, so UV or visible light is probably a better way of saying it. I still think to talk about the "emissions of the analyte" specifically means what is sitting in the atomiser, not what is in the HCL. That's my opinion.
In AAS, the analyte emission spectra (from hollow cathode lamp) is shown at the analyte, which absorbs the radiation. Thus we are measuring the absorption of the emission spectra. This emission spectra is not emitted by the analyte in sample, but it is emitted by standardized analyte in the cathode lamp.
One thing to stress is that AAS is know for discrete emission lines. I think it is incomplete to say it is absorption of visible and UV light, which can mean a continuous spectrum is being generated at the source.
In AES, we are not measuring absorption, we are measuring the amount of emission.
Post by: Mao on June 12, 2011, 01:19:37 am
I believe the answer is C.I think that disagrees with the definition of analyte though. Analyte is specifically the thing you are measuring - in this case the concentration of. I agree that neither B nor A is a perfect answer either, because, as you say, you are measuring discrete wavelengths, probably only one, in which case UV and visible light are not both used, so UV or visible light is probably a better way of saying it. I still think to talk about the "emissions of the analyte" specifically means what is sitting in the atomiser, not what is in the HCL. That's my opinion.
In AAS, the analyte emission spectra (from hollow cathode lamp) is shown at the analyte, which absorbs the radiation. Thus we are measuring the absorption of the emission spectra. This emission spectra is not emitted by the analyte in sample, but it is emitted by standardized analyte in the cathode lamp.
One thing to stress is that AAS is know for discrete emission lines. I think it is incomplete to say it is absorption of visible and UV light, which can mean a continuous spectrum is being generated at the source.
In AES, we are not measuring absorption, we are measuring the amount of emission.
I am not convinced by that argument, but I will agree that the options are ambiguously worded. If we take the interpretation that analyte refers to atoms in the atomiser, option C wouldn't make any physical sense. Absorption of emission would imply a decrement in emission by analyte in the atomiser, but such thing cannot be measured since initial emission intensity cannot be measured, thus absorbance cannot be calculated. In my opinion, it is a poor use of the word 'analyte'. If we assume used the word 'analyte' as a loose term (i.e. 'analyte in the instrument' = HCL, where analyte = metal of interest), it is exactly the principle of AAS. Another thing to consider is that the analyte depends on which HCL you use, so their loose use of 'analyte' may be justifiable.
I'm just a bit caught up on metal atoms absorbing visible and UV light. I still believe the most important thing we learn about AAS is that discrete spectra are emitted and absorbed, giving rise to its selectivity and sensitivity. The emission range is less important, and a question should not be testing this aspect.
@Water, do you have the solutions to this problem?
Post by: homosapiens on June 12, 2011, 10:17:57 am
Post by: thushan on June 12, 2011, 10:31:25 am
Well, that's what I think anyway.
Post by: Water on June 12, 2011, 10:37:25 am
Post by: thushan on June 12, 2011, 11:57:34 am
<This is not talking about GC or HPLC with Rt>
Post by: luken93 on June 12, 2011, 11:59:04 am
Post by: luken93 on June 12, 2011, 12:10:15 pm
Loving all these last minute things appearing in my head :S
Post by: thushan on June 12, 2011, 12:16:25 pm
As far as I know, and from what I've seen in practice papers, the Rf will always stay the same no matter what the conditions - unless you change the mobile/stationary phase.
That's what I thought, but QAT 2011 and http://orgchem.colorado.edu/hndbksupport/TLC/TLCrf.html says otherwise...
Post by: luken93 on June 12, 2011, 12:21:10 pm
Hmmmm, I'm sure VCAA had a question that had "which factors won't increase Rf" questions, and I'm quite sure it had temp that won't change it...As far as I know, and from what I've seen in practice papers, the Rf will always stay the same no matter what the conditions - unless you change the mobile/stationary phase.
That's what I thought, but QAT 2011 and http://orgchem.colorado.edu/hndbksupport/TLC/TLCrf.html says otherwise...
Post by: thushan on June 12, 2011, 12:26:25 pm
Post by: Andiio on June 12, 2011, 12:27:40 pm
I thought temperature would change the movement of both the component & the solvent itself in equal proportions like what you said, so Rf remains the same? :\
Post by: nacho on June 12, 2011, 12:28:34 pm
but there is also
retention time, Rt, which is different
Post by: thushan on June 12, 2011, 12:54:42 pm
Rf = Retardation and not retention factor...right? Haha insecurity.
I thought temperature would change the movement of both the component & the solvent itself in equal proportions like what you said, so Rf remains the same? :\
Yeah, that's what I thought. I'm now trying to see why QAT says otherwise...
Post by: Water on June 12, 2011, 01:01:18 pm
Rf = Retardation and not retention factor...right? Haha insecurity.
I thought temperature would change the movement of both the component & the solvent itself in equal proportions like what you said, so Rf remains the same? :\
Yeah, that's what I thought. I'm now trying to see why QAT says otherwise...
How can this possibly be true? They all have different MP/TP for the components. Their movements would be distinctly different to one another.
Its like comparing beef to pig, both have different rates that they will cook. Amping up the temperature won't mean, they will cook at the same speed.
My take on it *
Post by: nacho on June 12, 2011, 01:36:26 pm
Whats the relationship between amino acids, proteins and enzymes
are proteins polymers of amino acids?
are pH indicators composed of amino acids? ie do the constituents consist of amino acids? (i've just heard of ph indicators as 'buffer solutions' so many times, so was just curious)
chemically, what is a 'buffer'?
Post by: mickeymouse on June 12, 2011, 01:47:23 pm
Post by: Sakigami on June 12, 2011, 01:50:25 pm
As you know the hydroxide ion OH- is formed in an acid/base reaction with water acting as an acid. If NaOH is a strong base then, do the OH groups in amino acid side groups do the same thing in certain pH solutions or are they completely unrelated things? :S
Post by: DisaFear on June 12, 2011, 01:54:54 pm
And a polypeptide is a bunch of amino acids, which are the monomers
Right?
Post by: thushan on June 12, 2011, 02:03:11 pm
I have a quick question,
As you know the hydroxide ion OH- is formed in an acid/base reaction with water acting as an acid. If NaOH is a strong base then, do the OH groups in amino acid side groups do the same thing in certain pH solutions or are they completely unrelated things? :S
Careful here. NaOH only acts as a base here because it has Na+ and OH- already in the lattice; OH- acts as the base.
With the hydroxy groups, eg. Ser-CH2-OH, they are definitely not basic. If anything they are very very very very very weakly acidic (weaker acids than even water).
Post by: Greatness on June 12, 2011, 02:19:00 pm
question:Amino acids form polypeptides which form proteins and enzymes.
Whats the relationship between amino acids, proteins and enzymes
are proteins polymers of amino acids?
Post by: pi on June 12, 2011, 02:21:57 pm
Proteins are biochemical compounds consisting of one or more polypeptides
And a polypeptide is a bunch of amino acids, which are the monomers
Right?
I'd just say proteins are long polypeptides, insulin is the smallest with 51 amino acids (i think). Both have amino acids as monomers
Post by: Sakigami on June 12, 2011, 02:30:03 pm
I have a quick question,
As you know the hydroxide ion OH- is formed in an acid/base reaction with water acting as an acid. If NaOH is a strong base then, do the OH groups in amino acid side groups do the same thing in certain pH solutions or are they completely unrelated things? :S
Careful here. NaOH only acts as a base here because it has Na+ and OH- already in the lattice; OH- acts as the base.
With the hydroxy groups, eg. Ser-CH2-OH, they are definitely not basic. If anything they are very very very very very weakly acidic (weaker acids than even water).
Alrighty, thanks for that. :)
Post by: mickeymouse on June 12, 2011, 03:24:41 pm
Post by: jane1234 on June 12, 2011, 03:34:25 pm
how do the H NMR peaks split for butane?One triplet and one quartet I'm fairly sure, someone correct me if I'm wrong...
Also, what's the difference between distilled water and deionised water and what is each used for?
Post by: mickeymouse on June 12, 2011, 03:38:52 pm
Post by: taqi on June 12, 2011, 04:03:36 pm
Post by: jane1234 on June 12, 2011, 04:09:02 pm
okay kinda confused... how come the two CH2 in butane has a quartet peak but the CH2 in propane has a peak split into 7?
You have to look at which environments are identical.
The CH2 in butane is next to a CH3 (which gives it the quartet) and another CH2.
However, that CH2 is IDENTICAL to the other CH2, as they only account for one peak on the low res 1H NMR. They are in the same chemical environment as each other.
Identical groups won't cause splitting, only the ones that are adjacent and different.
With symmetrical molecules (like butane) I like to cut it in half and count the high res splits that way. So you would just look at the CH3CH2 when deciding splitting, as butane is the same on both sides.
With propane, however, the CH2 is next to two groups that are different from itself, so you take both CH3 groups into account when deducing the splitting pattern.
Hope that made some sort of sense, not sure of the exact theory behind the identical-environment-no-splitting, but that's basically how you work it out... :)
Post by: lilaznkev1n on June 12, 2011, 04:14:21 pm
I'm planning to do vcaa 08 sample on tuesday but not sure which one to do tomorrow.
I've done everything except vcaa 08 sample, tssm 09, tssm 10, tsfx 10.
Ill probably only do two more before the exam so I'll do vcaa 08 (sample) and which other one?
Post by: Greatness on June 12, 2011, 04:16:10 pm
Post by: mickeymouse on June 12, 2011, 04:28:43 pm
okay kinda confused... how come the two CH2 in butane has a quartet peak but the CH2 in propane has a peak split into 7?
You have to look at which environments are identical.
The CH2 in butane is next to a CH3 (which gives it the quartet) and another CH2.
However, that CH2 is IDENTICAL to the other CH2, as they only account for one peak on the low res 1H NMR. They are in the same chemical environment as each other.
Identical groups won't cause splitting, only the ones that are adjacent and different.
With symmetrical molecules (like butane) I like to cut it in half and count the high res splits that way. So you would just look at the CH3CH2 when deciding splitting, as butane is the same on both sides.
With propane, however, the CH2 is next to two groups that are different from itself, so you take both CH3 groups into account when deducing the splitting pattern.
Hope that made some sort of sense, not sure of the exact theory behind the identical-environment-no-splitting, but that's basically how you work it out... :)
that makes heaps of sense thanks so much!
Post by: thushan on June 12, 2011, 04:52:47 pm
exactly what makes DNA acidic or a nuleic acid? i read somewhere its the OH groups on the phosphate group able to donate protons, but i thought hydroxy groups dont donate protons!
OH does not donate a proton if it's bonded to carbon, you're right. But this OH is bonded to phosphorus, and it will happily donate a proton (the conjugate base is stable). Same thing for OH bonded to sulfur - i.e. sulfuric acid.
Post by: ttn on June 12, 2011, 06:55:02 pm
Post by: Sakigami on June 12, 2011, 07:07:26 pm
tssm are terrible imo the questions are written shockingly. stay away from them hahah
QFT. I decided to do a couple of the TSSM exams today, and some of their answers are very wishy-washy.
Post by: luken93 on June 12, 2011, 07:11:05 pm
How do you do the pH questions where it asks how many moles of HCl needs to be added to change the pH of a 1.0 L solution from 12 to 2?I do c1V1 = c2V2, dunno if there's a better way?
Remember that pH = 1x10^-pH, hence a pH of 2 = 1x10^-2 of H+ ions.
Post by: DavidSheena on June 12, 2011, 07:39:31 pm
d. Indentify two advantages of HPLC over TLC specific to the purpose of identifying the possible danger presented by liquid X.
My Ans: Hplc provides much more accurate seperation of components which allows for better, specific identification when compared with a standard chromatagram.
Would that be the same as better resolution than TLC so components are easily differentiated?
And when drawing nucleotides: Is it acceptable to leave the Hydrogens on as part of the hydroxyl group? Or should it be O-
Post by: scocliffe09 on June 12, 2011, 07:56:00 pm
For anyone who has done the KBT 2010; I marked myself harshly but I wanted to know if my answers were sufficient.hydroxyl retains the OH - not an acidic functional group generally.
d. Indentify two advantages of HPLC over TLC specific to the purpose of identifying the possible danger presented by liquid X.
My Ans: Hplc provides much more accurate seperation of components which allows for better, specific identification when compared with a standard chromatagram.
Would that be the same as better resolution than TLC so components are easily differentiated?
And when drawing nucleotides: Is it acceptable to leave the Hydrogens on as part of the hydroxyl group? Or should it be O-
On the phosphate, however, they are acidic. I think Thushan answered this a few hours ago. Without having done the KBT exam your answer looks decent; resolution and differentiation are far better words to use though.
Post by: ttn on June 12, 2011, 08:02:08 pm
How do you do the pH questions where it asks how many moles of HCl needs to be added to change the pH of a 1.0 L solution from 12 to 2?I do c1V1 = c2V2, dunno if there's a better way?
Remember that pH = 1x10^-pH, hence a pH of 2 = 1x10^-2 of H+ ions.
lol I don't get it?
Post by: mickeymouse on June 12, 2011, 08:22:06 pm
exactly what makes DNA acidic or a nuleic acid? i read somewhere its the OH groups on the phosphate group able to donate protons, but i thought hydroxy groups dont donate protons!
yup I just encountered this in the neap 2008 if it helps the solutions says the OH on the phosphate acts as an acid as it donates a proton, I think you have to take into account the environment of the phosphate.
okay question - the solutions also have that 5.5mg/mL = 0.099mol/L? I got 307.5M
edit: realized I multiplied by molar mass instead of divided sorry
Post by: Lols123 on June 12, 2011, 08:25:47 pm
just did it (my first timed exam) and only got 88% :(
not looking forward to wednesday :/
Post by: extcar on June 12, 2011, 08:35:36 pm
1. Carbon monoxide reacts with oxygen as described by the chemical equation:
2CO(g) +O2 (g) ---> 2CO2 (g)
When 20mL of CO reacts with 80mL of O2 at the same temperature and pressure, what is the volume of the gas mixture after the reaction has reached completion?
Answer is 90mL
2. 5.00g of a mixture of magnesium and zinc was allowed to completely react with dilute sulfuric acid as described by the chemical equation, where M represents either magnesium or zinc
M (s) +H2SO4 (aq) ---> MSO4 (aq) +H2 (g)
If 0.250g of hyrdrogen gas was produced in the reaction, what would the percentage composition of magnesium in the mixture be?
Answer is 37.6%
thanks!
sorry i only read the OT now! but if anyone wants to give it a try anyway ? :D
Post by: b^3 on June 12, 2011, 08:36:09 pm
How do you do the pH questions where it asks how many moles of HCl needs to be added to change the pH of a 1.0 L solution from 12 to 2?I do c1V1 = c2V2, dunno if there's a better way?
Remember that pH = 1x10^-pH, hence a pH of 2 = 1x10^-2 of H+ ions.
lol I don't get it?
i'm not sure if this is right, so someone check
so ph of 12 means
and V1=1L, now
and V2=1L
and we know that
so
so now we need to work out the number of mol needed right?
so
so the difference is how much we need to add so
im not 100% sure so someone just check to make sure.
Post by: b^3 on June 12, 2011, 08:40:56 pm
since CO:O2 is 2:1 we need 10mL of O2 for 20mL of CO
so that means that all the CO is used up but there is 80mL-10mL=70mL of O2 remaining
The amoutn of gas produced is this plus the amount of CO2
so v(CO2)=v(CO)=20mL
so add the two and well 70mL + 20mL = 90mL of gas after completion
Post by: ttn on June 12, 2011, 08:44:46 pm
How do you do the pH questions where it asks how many moles of HCl needs to be added to change the pH of a 1.0 L solution from 12 to 2?I do c1V1 = c2V2, dunno if there's a better way?
Remember that pH = 1x10^-pH, hence a pH of 2 = 1x10^-2 of H+ ions.
lol I don't get it?
i'm not sure if this is right, so someone check
so ph of 12 means
and V1=1L, now
and V2=1L
and we know that
so
so now we need to work out the number of mol needed right?
so
so the difference is how much we need to add so
im not 100% sure so someone just check to make sure.
That's what I did, but none of the options had that as an answer.
Post by: b^3 on June 12, 2011, 08:47:33 pm
so im guessing if i know where you got this from then option D)?
Post by: mickeymouse on June 12, 2011, 08:48:16 pm
ok so we know that since temperature and pressure remains the same the volume and amount (in mol) are related so.
since CO:O2 is 2:1 we need 10mL of O2 for 20mL of CO
so that means that all the CO is used up but there is 80mL-10mL=70mL of O2 remaining
The amoutn of gas produced is this plus the amount of CO2
so v(CO2)=v(CO)=20mL
so add the two and well 70mL + 20mL = 90mL of gas after completion
how do we know that v(CO2)=v(CO)=20mL?
Post by: b^3 on June 12, 2011, 08:52:19 pm
i got the solution for the second one but it may take a while to put up.
Post by: mickeymouse on June 12, 2011, 08:56:34 pm
becuase the temperature and pressure is constant you can use the nmol ratios for the voulme.
i got the solution for the second one but it may take a while to put up.
oh right thanks. just to clarify if it produced for example... 4CO2 would the volume be 20mL x 4? and if other products were produced could I use this ratio to find their volume?
Post by: b^3 on June 12, 2011, 09:01:18 pm
can someone help me with these questions, answers are there but i don't know how to work it out:
1. Carbon monoxide reacts with oxygen as described by the chemical equation:
2CO(g) +O2 (g) ---> 2CO2 (g)
When 20mL of CO reacts with 80mL of O2 at the same temperature and pressure, what is the volume of the gas mixture after the reaction has reached completion?
Answer is 90mL
2. 5.00g of a mixture of magnesium and zinc was allowed to completely react with dilute sulfuric acid as described by the chemical equation, where M represents either magnesium or zinc
M (s) +H2SO4 (aq) ---> MSO4 (aq) +H2 (g)
If 0.250g of hyrdrogen gas was produced in the reaction, what would the percentage composition of magnesium in the mixture be?
Answer is 37.6%
thanks!
sorry i only read the OT now! but if anyone wants to give it a try anyway ? :D
ok so we know that n(H2)=m/M = .250/2 = .125mol
and
so since
so
now multiply by 65.41
so
so now do the percentage by mass
%(Mg)
did that help?
Post by: b^3 on June 12, 2011, 09:02:52 pm
Post by: extcar on June 12, 2011, 09:09:46 pm
and you worked it out real quick too!
Post by: b^3 on June 12, 2011, 09:12:10 pm
Post by: jane1234 on June 12, 2011, 10:06:27 pm
Post by: luken93 on June 12, 2011, 10:09:54 pm
Is an alkene (C=C bond) considered a functional group?I think it is, but I'd await confirmation from the higher powers.
Benzene also is...
Post by: b^3 on June 12, 2011, 10:11:35 pm
Is an alkene (C=C bond) considered a functional group?
I'd say yes because it influences the properties of the molecule but i'm not sure. I'd like to find out though. According to this it is so -> http://chemed.chem.purdue.edu/genchem/topicreview/bp/2organic/function.html
Post by: jane1234 on June 12, 2011, 10:13:10 pm
Is an alkene (C=C bond) considered a functional group?I think it is, but I'd await confirmation from the higher powers.
Benzene also is...
higher powers? :D
And TSFX said they aren't "strictly" functional groups... but this was a VCAA sample exam so maybe it is :P
Post by: DisaFear on June 12, 2011, 10:14:03 pm
However, carbon can form covalent bond with other atoms or groups of atoms. These are called functional groups. A functional group is an atom or group of atoms that give a characteristic set of chemical properties to a molecule containing that group
I'd say yes because it influences the properties of the molecule but i'm not sure. I'd like to find out though. According to this it is so -> http://chemed.chem.purdue.edu/genchem/topicreview/bp/2organic/function.html
Are you sure that link wasn't referring to the Br thingy?
Edit: nvm, read on
Post by: luken93 on June 12, 2011, 10:31:20 pm
WHAT ARE THE CORRECT STATES FOR THE FERMENTATION OF GLUCOSE -> ETHANOL + CO2!
Post by: scocliffe09 on June 12, 2011, 10:33:25 pm
Is an alkene (C=C bond) considered a functional group?I think it is, but I'd await confirmation from the higher powers.
Benzene also is...
higher powers? :D
And TSFX said they aren't "strictly" functional groups... but this was a VCAA sample exam so maybe it is :P
Benzene is definitely a functional group.
Double bonds are not strictly but can be counted as a functional group according to VCAA, especially if there's nothing else to talk about.
Post by: acinod on June 12, 2011, 10:52:04 pm
Okay, so I've done 3 different exams with 3 different states.
WHAT ARE THE CORRECT STATES FOR THE FERMENTATION OF GLUCOSE -> ETHANOL + CO2!
Based on past VCAA Assessment Reports:
For fermentation, Glucose and Ethanol are aqueous while CO2 is a gas.
For combustion, O2 and CO2 are gas while Ethanol and H2O could be liquid or gas.
Post by: luken93 on June 12, 2011, 10:55:27 pm
Cheers!Okay, so I've done 3 different exams with 3 different states.
WHAT ARE THE CORRECT STATES FOR THE FERMENTATION OF GLUCOSE -> ETHANOL + CO2!
Based on past VCAA Assessment Reports:
For fermentation, Glucose and Ethanol are aqueous while CO2 is a gas.
For combustion, O2 and CO2 are gas while Ethanol and H2O could be liquid or gas.
Post by: Dr.Lecter on June 12, 2011, 10:57:02 pm
Post by: mickeymouse on June 13, 2011, 10:54:08 am
Post by: luken93 on June 13, 2011, 10:57:59 am
Post by: nacho on June 13, 2011, 11:32:06 am
i forgot those.
for solids and liquids! help
Post by: Greatness on June 13, 2011, 11:35:34 am
Post by: homosapiens on June 13, 2011, 02:17:38 pm
2. When say ethane reacts with chlorine when there's UV light, is CH3CH2Cl the only possibility, ie can CH2ClCH2Cl also be formed? And if so is it just that chloropropane is more likely than 1,2-dichloropropane...
Post by: nacho on June 13, 2011, 02:44:18 pm
holy crap, im gonna cram for aspirin 6 hours after accounting exam tmrw..
Post by: thushan on June 13, 2011, 03:06:19 pm
1. What kinds of reactions does benzene undergo? I would have thought combustion and addition (because of the double bonds) but apparently it's substitution, not addition? Is this because the shape must be maintained?
2. When say ethane reacts with chlorine when there's UV light, is CH3CH2Cl the only possibility, ie can CH2ClCH2Cl also be formed? And if so is it just that chloropropane is more likely than 1,2-dichloropropane...
1. [OUT OF COURSE] Benzene undergoes substitution because the fact that it's aromatic makes it highly stable; if you try to add to benzene you have to break this stability, this aromaticity, and that's unfavourable. Benzene instead undergoes substitution, that's correct. You don't need to know this though - I think all you need to know is that benzene does not act like a normal alkene.
2. Yes, you can get two chlorines thrown in. In fact, you can get as many chlorines thrown in as you want; it depends on the relative proportions of chlorine and ethane - whether chlorine is in excess or not.
Post by: nacho on June 13, 2011, 03:13:27 pm
i still dont get the diffrence between
beta-d-glucose and galactose
they look the exact same?
Post by: thushan on June 13, 2011, 03:21:30 pm
Post by: pi on June 13, 2011, 03:22:51 pm
WHAT DO I NEED TO KNOW FOR ASPIRIN??
holy crap, im gonna cram for aspirin 6 hours after accounting exam tmrw..
You don't need to any specifics actually. It only might be helpful to know what happens, but it isn't essential knowledge
Post by: nacho on June 13, 2011, 03:54:26 pm
Beta-d-glucose and Galactose differ at carbon 4; in galactose the OH sticks up, in glucose the OH sticks down.
wait i thought it was:
a-glucose, OH sticks down
B-glucose, OH sticks up
and what about alpha-glucose, how does that differ from galactose, if my thoughts are incorrect
Post by: azure on June 13, 2011, 04:14:45 pm
2011 Insight, Q6b
I was wondering about the carboxylic func. group on the other end of alanine... would that make it acidic in water as well?
Post by: cltf on June 13, 2011, 04:21:21 pm
Hello I need a little help with this question please, very unsure even though I've read the solutions.
2011 Insight, Q6b
I was wondering about the carboxylic func. group on the other end of alanine... would that make it acidic in water as well?
It would be basic because the dipeptide has more NH2 functional groups than COOH. If you imagine sticking the dipeptide in water, the COOH will DONATE, whilst the NH2 will ACCEPT, but overall more is accepted than is donated. Thus if it accepts more it is more basic.
Post by: azure on June 13, 2011, 04:24:44 pm
Hello I need a little help with this question please, very unsure even though I've read the solutions.
2011 Insight, Q6b
I was wondering about the carboxylic func. group on the other end of alanine... would that make it acidic in water as well?
It would be basic because the dipeptide has more NH2 functional groups than COOH. If you imagine sticking the dipeptide in water, the COOH will DONATE, whilst the NH2 will ACCEPT, but overall more is accepted than is donated. Thus if it accepts more it is more basic.
Ohhhhh so taking into account of the NH2 in the side chains as well? Thank you! Understand now :)
Post by: luken93 on June 13, 2011, 04:45:45 pm
the very left carbon, glucose sticks down, galactose sticks up - this is 4-CBeta-d-glucose and Galactose differ at carbon 4; in galactose the OH sticks up, in glucose the OH sticks down.
wait i thought it was:
a-glucose, OH sticks down
B-glucose, OH sticks up
and what about alpha-glucose, how does that differ from galactose, if my thoughts are incorrect
The difference between a and b glucose is the very RIGHT carbon atom, a-glucose OH sticks down, b-glucose OH sticks up - this is 1-C
Post by: nacho on June 13, 2011, 04:52:27 pm
wouldnt that mean that a glucose is the same as glucose and b glucose is the same galactose?
Or am i just unable to comprehend the logic behind this..lol
sigh C+ for chem, why not
Post by: homosapiens on June 13, 2011, 05:08:10 pm
1. What kinds of reactions does benzene undergo? I would have thought combustion and addition (because of the double bonds) but apparently it's substitution, not addition? Is this because the shape must be maintained?
2. When say ethane reacts with chlorine when there's UV light, is CH3CH2Cl the only possibility, ie can CH2ClCH2Cl also be formed? And if so is it just that chloropropane is more likely than 1,2-dichloropropane...
1. [OUT OF COURSE] Benzene undergoes substitution because the fact that it's aromatic makes it highly stable; if you try to add to benzene you have to break this stability, this aromaticity, and that's unfavourable. Benzene instead undergoes substitution, that's correct. You don't need to know this though - I think all you need to know is that benzene does not act like a normal alkene.
2. Yes, you can get two chlorines thrown in. In fact, you can get as many chlorines thrown in as you want; it depends on the relative proportions of chlorine and ethane - whether chlorine is in excess or not.
Thanks thushan! Stumbled across the benzene one in a Neap topic test so I thought it'd be best to double check (:
Post by: homosapiens on June 13, 2011, 05:09:22 pm
Post by: mickeymouse on June 13, 2011, 05:14:14 pm
Post by: mickeymouse on June 13, 2011, 05:14:54 pm
Trying to categorise molecules into HPLC and GC: I know carbohydrates can't be vaporised, what about nucleic acids, lipids and proteins?
apparently proteins decompose upon heating so I don't think they will vaporize either
Post by: Andiio on June 13, 2011, 05:15:31 pm
Post by: homosapiens on June 13, 2011, 05:18:01 pm
just wanting some clarification: in fractional distillation involving a tower and crude oil those with a higher molecular mass are collected at the bottom (higher temperature) but fractional distillation in general would result in those with a lower molecular mass collected first and so they are at the bottom?
Not sure if this answers your question, but the temperature decreases up the column, and fractions with lower boiling points liquefy out first because the temperature drops below their boiling temperature first
Post by: homosapiens on June 13, 2011, 05:19:40 pm
Trying to categorise molecules into HPLC and GC: I know carbohydrates can't be vaporised, what about nucleic acids, lipids and proteins?
apparently proteins decompose upon heating so I don't think they will vaporize either
ok so just to confirm... carbohydrates and amino acids need to go through HPLC and lipids and nucleic acids can go through GC
Post by: lilaznkev1n on June 13, 2011, 05:33:59 pm
My book says hydrogen bonds form between C=O and H-N, I don't really get this because isn't this a peptide link which is a covalent bond?
Post by: homosapiens on June 13, 2011, 05:37:57 pm
really noob question but can you please explain the secondary structure of proteins. I know it is due to hydrogen bonds which will cause coiling and folding but I don't know much else.
My book says hydrogen bonds form between C=O and H-N, I don't really get this because isn't this a peptide link which is a covalent bond?
Yep, CONH is the peptide link between two adjacent amino acids, while the hydrogen bonding in a protein's secondary structure is the interaction between amino acids not necessarily directly next to each other in the chain. So for example the first amino acid may have hydrogen bonds with the 100th amino acid in the chain, which results in its secondary structure.
Post by: mickeymouse on June 13, 2011, 05:38:49 pm
the peptide link is covalent and is between the carboxyl group and amine group but that is the primary structure (between 2 amino acids)
the hydrogen bond between the C=O and NH is the secondary structure and can be between different amino acids on a protein CHAIN (many amino acids)... the diagrams of a coiled, foiled, etc polypeptide might help you... hope this made sense
Post by: luken93 on June 13, 2011, 05:43:31 pm
just wanting some clarification: in fractional distillation involving a tower and crude oil those with a higher molecular mass are collected at the bottom (higher temperature) but fractional distillation in general would result in those with a lower molecular mass collected first and so they are at the bottom?Smaller molecules generally have less/weaker dispersion forces. Since frac dist separates on principal of boiling point, the fractions collected at the top have the lowest boiling point = least intermolecular forces = smaller chain.
Why are the chem shift values for 13C huge in comparison with that of 1H?Not completely sure, and we don't need to know it, however I assume it's got something to do with the size of the atom and hence the amount of shielding that it places upon neighbouring atoms?
really noob question but can you please explain the secondary structure of proteins. I know it is due to hydrogen bonds which will cause coiling and folding but I don't know much else.The secondary structure involves hydrogen bonding between C=O and N-H on adjacent peptide linkages. This creates a perfect coiling structure - if you look at Q14 of VCAA 2009 you can see that it's a uniform coil that is evenly spaced.
My book says hydrogen bonds form between C=O and H-N, I don't really get this because isn't this a peptide link which is a covalent bond?
Post by: david10d on June 13, 2011, 05:49:21 pm
Trying to categorise molecules into HPLC and GC: I know carbohydrates can't be vaporised, what about nucleic acids, lipids and proteins?
apparently proteins decompose upon heating so I don't think they will vaporize either
ok so just to confirm... carbohydrates and amino acids need to go through HPLC and lipids and nucleic acids can go through GC
If the molecular mass is below 300, it can be analysed with GC. Just add it up the molecular mass to make sure.
Post by: lilaznkev1n on June 13, 2011, 06:35:30 pm
I get it now :)
Post by: n. on June 13, 2011, 06:45:14 pm
ii. Would you expect group D on the inhibitor drug to be largely polar or non-polar? Explain
your choice
"The group of atoms marked D on the drug would be largely non-polar. 1 mark
The side chain on isoleucine is non-polar. Only a non-polar or low-polarity group of
atoms will interact appreciably with this non-polar side chain"
so how do you know that isoleucine is non polar?
what does that even mean...? ive always been confused with this non polar and polar stuff.... :(
Post by: DavidSheena on June 13, 2011, 07:02:34 pm
d.ii Draw a grouping of atoms that would give rise to the triplet and doublet.
The answer was the methyl group and ethyl group joined together. Whereas I seperated the two and labelled correctly. Would that be correct? As in one of the commercial exams a similar question had the answer with the two seperated.
Edit also:
7a.ii The answers say that one mark is awarded for working out the mass of methanol. But I did it slightly differently by converting density to molarity and then working out volume. Does VCAA accept alternate methods?
Post by: extcar on June 13, 2011, 07:23:54 pm
it goes what fragment must have been lost from the molecular ion to account for the high peak at m/z 45?
I wrote H+ atom,
the assessor's report wrote H or H atom. and then they went on to say C2H5O+ was also accepted. The most common answer was H+. Does that mean H+ is wrong or right?
http://www.vcaa.vic.edu.au/vce/studies/chemistry/assessreports/2008/chemistry_assessrep_june08.pdf
Post by: tony3272 on June 13, 2011, 07:31:42 pm
for VCAA 2008, question 7d SA,I'm pretty sure that when you are talking about what's lost to cause the peak at a particular m/z you don't include the positive charge.
it goes what fragment must have been lost from the molecular ion to account for the high peak at m/z 45?
I wrote H+ atom,
the assessor's report wrote H or H atom. and then they went on to say C2H5O+ was also accepted. The most common answer was H+. Does that mean H+ is wrong or right?
http://www.vcaa.vic.edu.au/vce/studies/chemistry/assessreports/2008/chemistry_assessrep_june08.pdf
Post by: jackson1234 on June 13, 2011, 07:40:32 pm
the very left carbon, glucose sticks down, galactose sticks up - this is 4-CBeta-d-glucose and Galactose differ at carbon 4; in galactose the OH sticks up, in glucose the OH sticks down.
wait i thought it was:
a-glucose, OH sticks down
B-glucose, OH sticks up
and what about alpha-glucose, how does that differ from galactose, if my thoughts are incorrect
The difference between a and b glucose is the very RIGHT carbon atom, a-glucose OH sticks down, b-glucose OH sticks up - this is 1-C
you wont be examined on galactose. Its not even in the data book.
Post by: Greatness on June 13, 2011, 08:08:14 pm
Yep whatever lines you see on the mass spectrum are the components that have lost a group of atoms or an atom - these have a charge. The componenets that are lost dont have a charge.for VCAA 2008, question 7d SA,I'm pretty sure that when you are talking about what's lost to cause the peak at a particular m/z you don't include the positive charge.
it goes what fragment must have been lost from the molecular ion to account for the high peak at m/z 45?
I wrote H+ atom,
the assessor's report wrote H or H atom. and then they went on to say C2H5O+ was also accepted. The most common answer was H+. Does that mean H+ is wrong or right?
http://www.vcaa.vic.edu.au/vce/studies/chemistry/assessreports/2008/chemistry_assessrep_june08.pdf
a question about the last question in the neap 2011 exam....ii) Overall isoleucine is polar due to the COOH and NH2, but the z group or side chain is a 4 carbon back bone - which is non-polar. This section of the amino acid is non-polar hence it can interact with the non polar drug. You should know that a carbon back bone is non polar think about butane, pentane etc they are all non-polar.
ii. Would you expect group D on the inhibitor drug to be largely polar or non-polar? Explain
your choice
"The group of atoms marked D on the drug would be largely non-polar. 1 mark
The side chain on isoleucine is non-polar. Only a non-polar or low-polarity group of
atoms will interact appreciably with this non-polar side chain"
so how do you know that isoleucine is non polar?
what does that even mean...? ive always been confused with this non polar and polar stuff.... :(
If something is polar it has an overall charge or the electrons are dragged to one side due to the elctronegativity of one of the atoms.
Post by: luken93 on June 13, 2011, 08:10:00 pm
for VCAA 2008, question 7d SA,Nope, H+ is incorrect.
it goes what fragment must have been lost from the molecular ion to account for the high peak at m/z 45?
I wrote H+ atom,
the assessor's report wrote H or H atom. and then they went on to say C2H5O+ was also accepted. The most common answer was H+. Does that mean H+ is wrong or right?
http://www.vcaa.vic.edu.au/vce/studies/chemistry/assessreports/2008/chemistry_assessrep_june08.pdf
The reason why is because when a fragment is lost, it is an atom that has been lost, not an ion.
So if I ionise propane for arguments sake, and a C2H5+ fragment occurs, it means that CH3 has been lost, not CH3+.
Think of it this way, if we have a covalent bond between C-C which indicates that is sharing two electrons. I get an axe and put it through that bond, one of the carbons will keep the two electrons, and the other will be left 1 short. Hence, the fragment is the one that has lost an electron and thus has a positive charge, and the fragment lost has gained an electron and is satisfied.
DISCLAIMER: This is not actually how it works, but it's a simplified way of thinking about it.
The reason why they accepted C2H5+ is because they used the word "fragment" - this usually denotes the part of the molecule that has the + charge.
Post by: extcar on June 13, 2011, 10:46:02 pm
thanks people
Post by: Water on June 13, 2011, 11:16:00 pm
Is it possible to say that HNMR allows the identification of the basic backbone of an organic compound?
And can Infrared POSSIBLY be used for quantitative analysis.
Post by: ulbasour on June 13, 2011, 11:22:28 pm
When describing HNMR.
Is it possible to say that HNMR allows the identification of the basic backbone of an organic compound?
And can Infrared POSSIBLY be used for quantitative analysis.
On your first question, it isn't the best method without supplementary information from MS or IR.
And i don't think so for IR
Post by: ulbasour on June 13, 2011, 11:25:55 pm
I was UNder the impression GC and HPLC can be used for QUANTITATIVE analaysis by determine relative peak areas, hence allowing you do determine % concentration
On an exam i did the answer said to use a calibration curve, and use standard solutions etc, for the samples Rt, under analysis
Can anyone clear this up?
Post by: david10d on June 13, 2011, 11:29:07 pm
Question:
I was UNder the impression GC and HPLC can be used for QUANTITATIVE analaysis by determine relative peak areas, hence allowing you do determine % concentration
On an exam i did the answer said to use a calibration curve, and use standard solutions etc, for the samples Rt, under analysis
Can anyone clear this up?
Yep, correct.
You just plot a calibration curve with standards and then compare with your solution.
Post by: Water on June 13, 2011, 11:30:07 pm
When describing HNMR.
Is it possible to say that HNMR allows the identification of the basic backbone of an organic compound?
And can Infrared POSSIBLY be used for quantitative analysis.
On your first question, it isn't the best method without supplementary information from MS or IR.
And i don't think so for IR
I was asking if my definition for it was apprioriate? lol ):
Post by: ulbasour on June 13, 2011, 11:33:14 pm
When describing HNMR.
Is it possible to say that HNMR allows the identification of the basic backbone of an organic compound?
And can Infrared POSSIBLY be used for quantitative analysis.
On your first question, it isn't the best method without supplementary information from MS or IR.
And i don't think so for IR
I was asking if my definition for it was apprioriate? lol ):
Ah my bad... Probably would say "HNMR is used in identifying Hydrogen environments in a compound."
Post by: ulbasour on June 13, 2011, 11:34:07 pm
Question:
I was UNder the impression GC and HPLC can be used for QUANTITATIVE analaysis by determine relative peak areas, hence allowing you do determine % concentration
On an exam i did the answer said to use a calibration curve, and use standard solutions etc, for the samples Rt, under analysis
Can anyone clear this up?
Yep, correct.
You just plot a calibration curve with standards and then compare with your solution.
But why doesn't the peak area suffice?
Post by: chemkid_23 on June 13, 2011, 11:37:55 pm
Post by: luken93 on June 14, 2011, 08:44:34 am
what would a 70% on vcaa 2009 have gotten me?http://www.vcaa.vic.edu.au/vce/statistics/2009/section3/vce_chemistry_ga09.pdf
Post by: mickeymouse on June 14, 2011, 10:20:34 am
Post by: luken93 on June 14, 2011, 10:36:06 am
do hydrogen bonds exist between alcohol molecules so there are no dispersion forces?Nah, there are dispersion forces as well, but they're nothing in comparison to hydrogen bonding.
Take a look at the boiling point of Ethane vs Ethanol for proof.
Post by: azure on June 14, 2011, 11:52:37 am
Does erucic acid (C66 H126 O6) have any carbon-carbon double bonds? If so, how many?
Working out the no. of double bonds with DBE = 66 - 126/2 + 1 = 4
However, the answers work with the empirical formula of euric acid.
Working with DBE again but with the empirical formula would give 2 --> One C=C double bond and one C=O double bond?...
Question is... to work out the number of double bonds, do we use the empirical formula or the molecular formula? Because they'll give different answers....
Edit: Oops, forgot that there are 6 oxygens in the molecular formula of erucic acid.. does that mean there are 3 C=O? Hence one C=C double bond?
If so, that works out right.... hm.
Post by: homosapiens on June 14, 2011, 12:01:42 pm
Post by: chemkid_23 on June 14, 2011, 01:07:56 pm
Post by: luken93 on June 14, 2011, 01:10:47 pm
how do u read the grade distributions???First page is the Unit 3 Exam
Second page is your SACs
Third page is Unit 4 Exam.
The distributions represent how many marks were needed to attain a particular grade, ie 57/73 was needed for an A+ in 2009.
Exams are marked twice, hence why they are out of 146.
Post by: chemkid_23 on June 14, 2011, 01:17:20 pm
i was wondering why it was out of 146
Post by: RobM8 on June 14, 2011, 01:21:11 pm
Question regarding KBT exam question 2d)
Does erucic acid (C66 H126 O6) have any carbon-carbon double bonds? If so, how many?
Working out the no. of double bonds with DBE = 66 - 126/2 + 1 = 4Therefore there are 3 C=C double bonds and one C=O double bond.
However, the answers work with the empirical formula of euric acid.
Working with DBE again but with the empirical formula would give 2 --> One C=C double bond and one C=O double bond?...
Question is... to work out the number of double bonds, do we use the empirical formula or the molecular formula? Because they'll give different answers....
Edit: Oops, forgot that there are 6 oxygens in the molecular formula of erucic acid.. does that mean there are 3 C=O? Hence one C=C double bond?
If so, that works out right.... hm.
C66 H126 O6 is three euric acid molecules --> one euric acid molecule is then C22 H42 O2 which is the same as C21H41COOH
using CnH2n+1COOH --> there is one C=C bond in euric acid.
I wouldn't use DBE in this case as it needs an extra step to get rid of any C=O bonds you have calculated which you can forget to remove.
Post by: n. on June 14, 2011, 01:35:22 pm
Post by: luken93 on June 14, 2011, 01:36:24 pm
is peak area and peak height the same thing?Kinda, the reason why we normally just use height is because the width of the peaks is usually tiny, hence the height is usually a decent way to measure.
Post by: cltf on June 14, 2011, 01:37:05 pm
Post by: n. on June 14, 2011, 01:40:48 pm
Post by: homosapiens on June 14, 2011, 02:14:16 pm
Post by: mickeymouse on June 14, 2011, 02:40:09 pm
Post by: Sakigami on June 14, 2011, 02:51:44 pm
chloroalkanes , fluoroalkanes, etc do they all form hydrogen bonds with one another and only with water? what about the dispersion forces since they're hydrocarbons?
I didn't think chloroalkanes and fluoroalkanes can form hydrogen bonds with each other as there isn't any H bonded to F,O,N for them to form hydrogen bonds with. I believe that since they are polar, they would form dipole-dipole bonds if anything? If a chloroalkane or fluoroalkane has a long non-polar end, I suppose the net dispersion forces will be the strongest force of attraction between molecules.
But yes they do form hydrogen bonds with water as the H's are bonded to an O, allowing for hydrogen bonding to occur.
---------
Another question I have is in relation to calibration curves;
1 method of doing these questions is to use "dilation factors" to calculate the concentration in the sample. But I find its more logically to calculate the mass in the diluted sample and work backwards from here. Is this an acceptable method of working for these type of questions? :)
Post by: Greatness on June 14, 2011, 03:07:46 pm
I think you mean dilution factor? hahahchloroalkanes , fluoroalkanes, etc do they all form hydrogen bonds with one another and only with water? what about the dispersion forces since they're hydrocarbons?
I didn't think chloroalkanes and fluoroalkanes can form hydrogen bonds with each other as there isn't any H bonded to F,O,N for them to form hydrogen bonds with. I believe that since they are polar, they would form dipole-dipole bonds if anything? If a chloroalkane or fluoroalkane has a long non-polar end, I suppose the net dispersion forces will be the strongest force of attraction between molecules.
But yes they do form hydrogen bonds with water as the H's are bonded to an O, allowing for hydrogen bonding to occur.
---------
Another question I have is in relation to calibration curves;
1 method of doing these questions is to use "dilation factors" to calculate the concentration in the sample. But I find its more logically to calculate the mass in the diluted sample and work backwards from here. Is this an acceptable method of working for these type of questions? :)
Well yeah i just ratios so much easier - im assuming this is what you do? so you have to fractions and you gotta solve for x?..
Post by: Water on June 14, 2011, 04:07:33 pm
Which one is speaking the truth? I don't like some of KBT answers though.
Post by: DavidSheena on June 14, 2011, 04:10:20 pm
Post by: extcar on June 14, 2011, 04:12:49 pm
more titre= lower concentration of unknown
less titre= more concentration of unknown
Post by: homosapiens on June 14, 2011, 04:16:04 pm
KBT said Monosaccharides can be used in GC, whilst STAV says otherwise and it will decompose in GC.
Which one is speaking the truth? I don't like some of KBT answers though.
Yeah I just did the KBT paper and got stumped by that question too! I'm pretty sure monosaccharides cannot be vapourised so they aren't suited to GC since they decompose when heated, not absolutely sure though.
Is transmittance the amount of light/radiation absorbed or not absorbed?
Transmittance is the amount of light/radiation that transmits (passes through) the sample, therefore it is the amount that is not absorbed. If you get confused you can look at the IR spectrum - if there isn't a peak, transmittance is 100%, therefore it all transmits and is not absorbed by the bond
Post by: homosapiens on June 14, 2011, 04:19:25 pm
would this be a good thing to remember, as in does it make sense? or not..
more titre= lower concentration of unknown
less titre= more concentration of unknown
That makes sense for one straight titration, but if you look at the questions where two titrations are involved (back titration), it's actually the opposite, since the second titration is to see how much is left after reacting with the unknown sample that you're trying to find. Hope that makes sense :| Refer to LisaChem '09 Q5 if it doesn't
Post by: luken93 on June 14, 2011, 04:21:17 pm
would this be a good thing to remember, as in does it make sense? or not..Not necessarily, as the unknown can be in the conical flask or the burette.
more titre= lower concentration of unknown
less titre= more concentration of unknown
Is transmittance the amount of light/radiation absorbed or not absorbed?Transmittance is the opposite of absorbed, if you think about it this way, if the atoms absorb 20%, they will transmit 80% of the light.
KBT said Monosaccharides can be used in GC, whilst STAV says otherwise and it will decompose in GC.I would go with HPLC, as they generally decompose. However, I'm highly doubtful that VCAA will ever ask this. It's usually AAS vs UV-Vis vs IR vs GC/HPLC, never HPLC vs GC
Which one is speaking the truth? I don't like some of KBT answers though.
Post by: DavidSheena on June 14, 2011, 04:44:52 pm
Is transmittance the amount of light/radiation absorbed or not absorbed?Transmittance is the opposite of absorbed, if you think about it this way, if the atoms absorb 20%, they will transmit 80% of the light.
Thank You; Do we also need to know the ranges of colorimetry and so on? For example 400-750nm etc?
Post by: Andiio on June 14, 2011, 04:45:43 pm
would this be a good thing to remember, as in does it make sense? or not..Not necessarily, as the unknown can be in the conical flask or the burette.
more titre= lower concentration of unknown
less titre= more concentration of unknownIs transmittance the amount of light/radiation absorbed or not absorbed?Transmittance is the opposite of absorbed, if you think about it this way, if the atoms absorb 20%, they will transmit 80% of the light.KBT said Monosaccharides can be used in GC, whilst STAV says otherwise and it will decompose in GC.I would go with HPLC, as they generally decompose. However, I'm highly doubtful that VCAA will ever ask this. It's usually AAS vs UV-Vis vs IR vs GC/HPLC, never HPLC vs GC
Which one is speaking the truth? I don't like some of KBT answers though.
agreed, an HPLC vs GC question is, in most cases beyond the scope of our course.
I'm really paranoid about some weird as theory questions haha..
Post by: Andiio on June 14, 2011, 04:46:17 pm
Is transmittance the amount of light/radiation absorbed or not absorbed?Transmittance is the opposite of absorbed, if you think about it this way, if the atoms absorb 20%, they will transmit 80% of the light.
Thank You; Do we also need to know the ranges of colorimetry and so on? For example 400-750nm etc?
Nah you don't have to know the complementary colour wavelengths etc
I've never seen any Q's asking about transmittance and all :\
Post by: Andiio on June 14, 2011, 05:55:14 pm
can we write OH- as the catalyst as opposed to KOH/NaOH? Also do we have to specify that the OH-/KOH/NaOH is (aq)?
Thanks!
Also, when writing the 2nd part of the transesterification, do you use 1 fatty acid to make the methyl ester or are you supposed to use 3 to make 3x methyl ester? :|
Are we meant to write transesterification in 2 separate eqns or 1 combined eqn?
Post by: Sakigami on June 14, 2011, 06:33:40 pm
I think you mean dilution factor? hahahchloroalkanes , fluoroalkanes, etc do they all form hydrogen bonds with one another and only with water? what about the dispersion forces since they're hydrocarbons?
I didn't think chloroalkanes and fluoroalkanes can form hydrogen bonds with each other as there isn't any H bonded to F,O,N for them to form hydrogen bonds with. I believe that since they are polar, they would form dipole-dipole bonds if anything? If a chloroalkane or fluoroalkane has a long non-polar end, I suppose the net dispersion forces will be the strongest force of attraction between molecules.
But yes they do form hydrogen bonds with water as the H's are bonded to an O, allowing for hydrogen bonding to occur.
---------
Another question I have is in relation to calibration curves;
1 method of doing these questions is to use "dilation factors" to calculate the concentration in the sample. But I find its more logically to calculate the mass in the diluted sample and work backwards from here. Is this an acceptable method of working for these type of questions? :)
Well yeah i just ratios so much easier - im assuming this is what you do? so you have to fractions and you gotta solve for x?..
Yeah, I do ratios for some of those questions because it makes more sense to me. :P
What I meant was for instance, you determine c(Pb) in 10ml is = 20.0mg/L
So m(Pb) in 10ml is = 0.2mg
It's a 10ml aliquot from the 100ml flask it originally come from;
m(Pb) in 100ml = 2.0mg
And you're asked to find the concentration of Pb in a 2.0g sample.
% Pb = 2.0 * 10^3 g / 2.0g * 100 = 0.1%
Rather than doing that messy dilution factor some of these practice exams go on about. :S
Post by: luken93 on June 14, 2011, 07:04:31 pm
As much as we can orr? It's just that it's hardly ever mentioned/shown in the assessors report? It's only ever shown if the question actually asks "what is the common reagent catalysts etc etc"
Post by: Sakigami on June 14, 2011, 07:12:26 pm
So, when do we add catalysts?
As much as we can orr? It's just that it's hardly ever mentioned/shown in the assessors report? It's only ever shown if the question actually asks "what is the common reagent catalysts etc etc"
Yeah, I noticed this too in the practice exams and VCAA exams that they don't seem to mention the catalysts for answers where they haven't specifically asked for them. Personally; if you know them very well, I would suggest you write them down just in case. VCAA may choose to be picking about catalysts this year, so you really don't want to give them reason to deduct marks. A similar case was with the naming of that amine in a past year exam where it wasn't a problem in the past, but they decided to be very picky about it from that year onwards. So I think its good safety measure to include your catalysts. :P
Having said that though; if you write the wrong catalyst, that's probably more reason for them to deduct marks so I think its a matter of personal choice.
Post by: GuessWho on June 14, 2011, 07:53:27 pm
Post by: david10d on June 14, 2011, 07:56:59 pm
Post by: GuessWho on June 14, 2011, 07:58:51 pm
Post by: vea on June 14, 2011, 08:01:50 pm
Post by: homosapiens on June 14, 2011, 09:17:32 pm
Post by: Mao on June 14, 2011, 09:27:15 pm
Last minute question: but-2-ene is subjected to high temperature and pressure, what will it become?
Probably polymerizes.
Post by: Lols123 on June 14, 2011, 09:31:51 pm
one more practice paper? looking over notes?
Post by: luken93 on June 14, 2011, 09:35:28 pm
what are you guys doing atm?Watching telly :P
one more practice paper? looking over notes?
Post by: Lols123 on June 14, 2011, 09:43:27 pm
does it work like this: the closer the H or C atom is to an electronegative atom like O, the more downfield it is?
Post by: DisaFear on June 14, 2011, 09:43:47 pm
what are you guys doing atm?
one more practice paper? looking over notes?
Yes, doing one more practice paper, then notes revision
Then gonna end the night with a game or two :P
Then i've got the train and tomorrow to study
Are there any tables around showing what factors increase/decrease titration values/what-not with explanations?
Like "It wasn't filtered properly so it should be heavier than expected, means this is less/more,etc"
Post by: azure on June 14, 2011, 09:46:58 pm
what are you guys doing atm?
one more practice paper? looking over notes?
Hahaha, last minute read over my notes... (would be shocking if I'm still learning new things! D= ) Pretty tired from a last day of cramming so off to have an early night soon. =) Have fun tomorrow.
Post by: azure on June 14, 2011, 09:50:33 pm
would VCAA ever ask us predict how downfield a chemical shift is judging from a structure?
does it work like this: the closer the H or C atom is to an electronegative atom like O, the more downfield it is?
Hmm... this would be about how much deshielding/shielding there is. According to my school, we don't need to know about it.... but would be helpful to understand that the closer it is to a functional group such as COOH, the more downfield that H atom will be. If I'm wrong, please correct me.
Post by: Water on June 14, 2011, 09:51:52 pm
Thought, I was being a retard for asking it haha. Felt self conscious, but I shall be studying an extra 2 hours .... School bright and early :)
Post by: DisaFear on June 14, 2011, 09:52:38 pm
lol aite, thanks, deleted my other post. Peow >:!.
Yes, causing me to delete mine lol, lest people wonder about my sanity
Post by: Greatness on June 14, 2011, 09:54:55 pm
Yep the closer a H or C is to an electronegative atom the more it will be shifted downfield.would VCAA ever ask us predict how downfield a chemical shift is judging from a structure?
does it work like this: the closer the H or C atom is to an electronegative atom like O, the more downfield it is?
Hmm... this would be about how much deshielding/shielding there is. According to my school, we don't need to know about it.... but would be helpful to understand that the closer it is to a functional group such as COOH, the more downfield that H atom will be. If I'm wrong, please correct me.
Post by: GuessWho on June 14, 2011, 09:57:09 pm
Post by: Lols123 on June 14, 2011, 09:58:06 pm
Post by: azure on June 14, 2011, 09:59:06 pm
did you guys bother learning all the penicillin stuff
Penicillin....?! There was stuff about penicillin?! D=
Post by: Lols123 on June 14, 2011, 10:01:30 pm
havent seen it tested anywhere though
Post by: DisaFear on June 14, 2011, 10:01:33 pm
Post by: Asx4Life on June 14, 2011, 10:04:44 pm
Post by: Greatness on June 14, 2011, 10:05:42 pm
Just to clarify, When esterification occurs which loses the OH group. Alcohol or Acid? I assume same thing goes for glycerol and fatty acids.
Actually im not too sure :P
Post by: DisaFear on June 14, 2011, 10:08:11 pm
http://www.titrations.info/titration-errors
You probably cant use half of them on the exam though
Post by: azure on June 14, 2011, 10:09:00 pm
Post by: vea on June 14, 2011, 10:10:38 pm
Just to clarify, When esterification occurs which loses the OH group. Alcohol or Acid? I assume same thing goes for glycerol and fatty acids.The carboxyl group loses the OH which is the acid.
Actually im not too sure :P
You were right, the carboxyl group loses the OH and the hydroxyl loses its H.
Post by: DisaFear on June 14, 2011, 10:11:59 pm
Came across on question telling me to give the semi structural formula of the triglyceride shown... how do we do that? As far as I know, I can only give the semi structural formula of glycerol... haha, but not both of them combined... =|
Why not?
Glycerol has an OH group
The fatty dudes have a carboxylic group
Add them and you get an ester
Post by: azure on June 14, 2011, 10:16:06 pm
Came across on question telling me to give the semi structural formula of the triglyceride shown... how do we do that? As far as I know, I can only give the semi structural formula of glycerol... haha, but not both of them combined... =|
Why not?
Glycerol has an OH group
The fatty dudes have a carboxylic group
Add them and you get an ester
Hrmm... what I mean is that I have trouble giving the semi structural formula... sure enough I know how to draw up the structural formula...
but hrmm..
let's say we're given glycerol + lauric acid
Would the semi structural just be: .... HOCH2CHOHCH2OH Okay already given up... don't know how to add the fatty acid into the semi structural formula.
Post by: Greatness on June 14, 2011, 10:19:28 pm
CH3(CH2)15COOCH3
Post by: DisaFear on June 14, 2011, 10:19:42 pm
There's a diagram in the Heinemann on page 179
Post by: azure on June 14, 2011, 10:23:18 pm
the fatty acid acts as the carboxylic acid; so you would get something like:
CH3(CH2)15COOCH3
Thank you!
Post by: azure on June 14, 2011, 10:24:10 pm
Which text book do you use?
There's a diagram in the Heinemann on page 179
Thanks =D Found the page :)
Post by: extcar on June 15, 2011, 12:07:53 am
Post by: scocliffe09 on June 15, 2011, 12:18:48 am
denaturing enzymes will change tertiary and secondary structures? yes???Yep.
Post by: homosapiens on June 15, 2011, 08:23:43 am
2. Will 100M of weak acid have the same concentration as 1M of a monoprotic strong acid?
Post by: DavidSheena on June 15, 2011, 08:38:01 am
1. When writing out the equation for oxidation from an alcohol to a carboxylic acid, does the H+/MnO4- go above the arrow or are they reactants?I'm not completely sure but hopefully someone corrects me.
2. Will 100M of weak acid have the same concentration as 1M of a monoprotic strong acid?
1. I generally put the MnO4- or Cr2O72- on top of the arrow and the H+ on the bottom.
2. Concentration has no effect on the strength of the acid and pretty sure its the other around too. Concentration refers to the AMOUNT of acid present in the solution. Whereas the strength of an acid is it's ability to ionise in aqueous solutions or donate a proton readily. Hope that makes sense.
Post by: banditkeith on June 15, 2011, 10:23:25 am
1. When writing out the equation for oxidation from an alcohol to a carboxylic acid, does the H+/MnO4- go above the arrow or are they reactants?I'm not completely sure but hopefully someone corrects me.
2. Will 100M of weak acid have the same concentration as 1M of a monoprotic strong acid?
1. I generally put the MnO4- or Cr2O72- on top of the arrow and the H+ on the bottom.
2. Concentration has no effect on the strength of the acid and pretty sure its the other around too. Concentration refers to the AMOUNT of acid present in the solution. Whereas the strength of an acid is it's ability to ionise in aqueous solutions or donate a proton readily. Hope that makes sense.
That is correct. At least for 1.
I'm quite positive 2 is too
Post by: homosapiens on June 15, 2011, 10:33:32 am