Post by: Mao on June 10, 2009, 02:13:12 pm
Let me know if I made any errors.
Congratulations to all :) you are FREE (for now..)
Errata:
Multiple Choice
MCQ 19 - B is technically correct
Short Answers
Question 3 (c)
If HCl was in the burette: Lower concentration of HCl, fixed number of moles of NaOH (in the aliquot) --> titre is greater. Hence calculated value will be higher than true.
If NaOH was in the burette: less number of moles of HCl (in the aliquot) --> titre is less. Hence calculated concentration of NaOH in the burette will be higher than true.
[I think either explanations will be fine]
Question 7, (a)
Step 1 is also correct, CO2 -> C6H12O6 is reduction +4 -> 0
Post by: ilovevce on June 10, 2009, 02:17:41 pm
Post by: Toothpaste on June 10, 2009, 02:19:44 pm
Post by: doboman on June 10, 2009, 02:30:19 pm
Mao don't tell me you're writing solutions to all the Monash University exams too ...
Funny how we 2008'ers open this thread and are impressed with the amount of dedication Mao has. Whereas the 2009'ers are like "OMG OMG ANSWERS" :)
Post by: monokekie on June 10, 2009, 02:34:27 pm
Post by: monokekie on June 10, 2009, 02:34:47 pm
OMGOMG ANSWERS!!!
THANKS MAO
Post by: vamsiaus on June 10, 2009, 02:42:37 pm
Post by: monokekie on June 10, 2009, 02:43:10 pm
Post by: ilovevce on June 10, 2009, 02:43:31 pm
i am not sure about multiple choice quesiton 5 and 6
In Q5, molecule A is the most non-polar (it contains only a straight alkane chain) whereas the others have polar functional groups such as NH2 and OH. These polar groups would bond more to the polar mobile phase and so would travel through the chromatograph quicker. Option A would bond more to the stationary phase and so would be retained for longer.
In Q6, W,X,Y,Z are all straight chain alkanes. The only form of intermolecular forces they have are dispersion forces. If the boiling point is greater, the longer the alkane chain, and so the more dispersion forces would arise between the alkane and the stationary phase. So a greater retention time means a greater boiling point.
Post by: methodsboy on June 10, 2009, 02:44:02 pm
Post by: vamsiaus on June 10, 2009, 02:44:11 pm
Post by: Toothpaste on June 10, 2009, 02:44:38 pm
what is the whole exam out of?73 says the cover
http://www.vcaa.vic.edu.au/vcaa/vce/exams/examcovers/June_2009_covers/2009chem1-cover.pdf
It didn't change right?
Post by: monokekie on June 10, 2009, 02:45:16 pm
Post by: hard on June 10, 2009, 02:51:01 pm
Post by: mystikal on June 10, 2009, 02:51:14 pm
Post by: monokekie on June 10, 2009, 02:53:35 pm
Post by: mystikal on June 10, 2009, 02:54:31 pm
Post by: monokekie on June 10, 2009, 02:57:18 pm
Post by: avram_grant on June 10, 2009, 02:57:34 pm
Post by: jess3254 on June 10, 2009, 02:59:27 pm
Post by: rhjc.1991 on June 10, 2009, 03:02:34 pm
Hey, was answer to q19 MC really D? because i got that and ppl said it was wrong.
Post by: dekoyl on June 10, 2009, 03:04:00 pm
it was out of 73.I got B but I don't doubt Mao too much aha.
Hey, was answer to q19 MC really D? because i got that and ppl said it was wrong.
Post by: avram_grant on June 10, 2009, 03:04:39 pm
Post by: /0 on June 10, 2009, 03:05:54 pm
C goes from +4 to 0?
Post by: rhjc.1991 on June 10, 2009, 03:09:47 pm
when they said X, do they mean the point above the surface of the liquid?In Q7a Short answer isn't Step 1 also reduction?
C goes from +4 to 0?
Yeah I put that too..
but ughhh :(
I had to go on enter calc and do some adjusting ahaha
me too!
When they say X do they mean the point above the liquid surface?
Post by: jules on June 10, 2009, 03:10:50 pm
or did i just overthink that question lol
Post by: rhjc.1991 on June 10, 2009, 03:11:16 pm
NO!!!! That means I got it wrong--I originally had 4
Post by: Mao on June 10, 2009, 03:13:40 pm
Post by: ilovevce on June 10, 2009, 03:18:17 pm
it was out of 73.I got B but I don't doubt Mao too much aha.
Hey, was answer to q19 MC really D? because i got that and ppl said it was wrong.
Technically, B would be correct. Some of the water would vaporise and then condense as it rose up the apparatus. However, the amount of vaporised water would be very small. Practically, the difference in percentage concentration of ethanol would be so small as to be insignificant.
This should have been an explanation question.
Post by: emkate on June 10, 2009, 03:21:03 pm
Post by: Mao on June 10, 2009, 03:21:42 pm
it was out of 73.I got B but I don't doubt Mao too much aha.
Hey, was answer to q19 MC really D? because i got that and ppl said it was wrong.
Technically, B would be correct. Some of the water would vaporise and then condense as it rose up the apparatus. However, the amount of vaporised water would be very small. Practically, the difference in percentage concentration of ethanol would be so small as to be insignificant.
This should have been an explanation question.
I agree with this, I have a feeling B and D will both be accepted.
we have a resident assessor who will be/have been reading this thread, who may wish to help us argue our point :)
Post by: monokekie on June 10, 2009, 03:24:27 pm
does anyone know what % they had to get last year to get an A+ ? i worked out my answers think i might have got around 86%.. what will that give me?
i guess around 40?
Post by: vamsiaus on June 10, 2009, 03:24:37 pm
Post by: avram_grant on June 10, 2009, 03:31:55 pm
Post by: Mao on June 10, 2009, 03:32:45 pm
Some ethanol forms an azeotrope with water (94~95% ethanol, 5~6% water). That is, this mixture does NOT separate when boiled. Hence in the vapour, there will definitely be some water.
Quote from: http://en.wikipedia.org/wiki/Azeotrope#Distillation_of_mixtures
For example, if a 50/50 mixture of ethanol and water is distilled once, the distillate will be 80% ethanol and 20% water (see ethanol data page), which is closer to the azeotropic mixture than the original. Distilling the 80/20% mixture produces a distillate that is 87% ethanol and 13% water. Further repeated distillations will produce mixtures that are progressively closer to the azeotropic ratio of 95.5/4.5%. No number of distillations, however, will ever result in a distillate that exceeds the azeotropic ratio. Likewise when distilling a mixture of ethanol and water that is richer in ethanol than the azeotrope, the distillate (contrary to intuition) will be poorer in ethanol than the original but slightly richer than the azeotrope.[2]
However, this is much beyond VCE level. And with VCE knowledge, D would seem the most obvious answer..
[note, the question itself is incorrect. The boiling point will be less than 78 degrees]
Post by: lukeperry91 on June 10, 2009, 03:36:37 pm
Will that be a common error?
Post by: mystikal on June 10, 2009, 03:48:11 pm
Post by: NE2000 on June 10, 2009, 03:51:20 pm
1. Carrier gas Q: I thought that H2 doesn't react with it but as we generally always use an inert gas do you think that will be the answer? I thought about what they wanted and wondered whether they were testing our ability to remember the gases (Ne, Ar, He) that can be used for GC or...whatever...anywayz
2. Fractional distillation Q: if D is right at VCE level and B is right, then could C also be right? Rushed that one...once in a part Biology paper I think VCAA gave marks to everyone coz the question was stuffed up. Hopefully they do that again :)
3. Was the stuffed up HCl put in the burette or the conical flask. Coz if in burette the titre would be larger and hence greater concentration. If in flask the titre would be smaller and hence greater concentration.
4. Went back, do you reckon they wanted Na+ and O-? Would ONa have sufficed?
That is all for now, very unhappy after getting out of the exam room but your solutions have lightened me up slightly.
Post by: NE2000 on June 10, 2009, 03:58:00 pm
Post by: avram_grant on June 10, 2009, 03:59:41 pm
Post by: lukeperry91 on June 10, 2009, 04:01:34 pm
hydrogen is highly flammable - so on that fact i didnt put hydrogen as it wouldnt be smart putting a flamable gas into a hot oven.... what do you guys think?Very interesting! Any thoughts Mao?
Post by: NE2000 on June 10, 2009, 04:04:55 pm
Post by: ilovevce on June 10, 2009, 04:08:18 pm
hydrogen is highly flammable - so on that fact i didnt put hydrogen as it wouldnt be smart putting a flamable gas into a hot oven.... what do you guys think?Very interesting! Any thoughts Mao?
With a bit of extra research - H2 can be used a carrier gas and is in fact one of the most efficient for achieveing separation. However, because of its flammability and other reasons, He is often preferred. But H2 could still be used.
Post by: methodsboy on June 10, 2009, 04:09:50 pm
if only these answers were posted up before the exam....
Post by: avram_grant on June 10, 2009, 04:15:35 pm
hydrogen is highly flammable - so on that fact i didnt put hydrogen as it wouldnt be smart putting a flamable gas into a hot oven.... what do you guys think?Very interesting! Any thoughts Mao?
With a bit of extra research - H2 can be used a carrier gas and is in fact one of the most efficient for achieveing separation. However, because of its flammability and other reasons, He is often preferred. But H2 could still be used.
You think they'd expect us to know that H2 could be use? In the chem books they usually say either nitrogen or helium - and when i went to VSEC to use the GLC i didnt see H2
Post by: avram_grant on June 10, 2009, 04:20:05 pm
Post by: Ilovemathsmeth on June 10, 2009, 04:23:38 pm
Post by: lacoste on June 10, 2009, 04:23:55 pm
It would be cool if you can repeat subjects, but unfair maybe. ;)
Post by: hyperblade01 on June 10, 2009, 04:31:52 pm
Wouldn't the titre be more as more HCl is required?
Post by: littlecherry25 on June 10, 2009, 04:37:42 pm
i don't know what letter i put
but i said that it the percentage increased at you get going higher
shit, now i know its wrong lol
Post by: m.hudson.1990 on June 10, 2009, 04:38:00 pm
Post by: avram_grant on June 10, 2009, 04:40:51 pm
Post by: turley on June 10, 2009, 04:42:04 pm
lets assume H2 gas is unsuitable since it is flammable.
wouldn't alkanes (more importantly the ones analyise in GC) also be flammable. obviously a conflict
Post by: NE2000 on June 10, 2009, 04:43:45 pm
Post by: NE2000 on June 10, 2009, 04:44:57 pm
for questions 12 in the MC, wouldnt it be 4? 1-chloro-2,2dimethyl butane, 2-chloro-2,2dimethyl butane., 2-chloro-3,3 dimethyl butane and 1-chloro-3,3-dimethyl butane
Just try putting dots next to the carbon where you are adding the chloro. The three left-most carbons are 'equivalent' in a way that adding a chloro to either of these will produce the same compound. So 3 I think is right.
Post by: m.hudson.1990 on June 10, 2009, 04:46:59 pm
Post by: kurrymuncher on June 10, 2009, 04:47:48 pm
Im ending it tonight
Post by: Ilovemathsmeth on June 10, 2009, 04:48:02 pm
to Ilovemathsmeth
lets assume H2 gas is unsuitable since it is flammable.
wouldn't alkanes (more importantly the ones analyise in GC) also be flammable. obviously a conflict
damn :(
what was the concentration effect on sodium hydrogencarbonate - higher as a result of the contaminated HCl?
Post by: avram_grant on June 10, 2009, 04:49:28 pm
Post by: turley on June 10, 2009, 04:49:32 pm
Post by: methodsboy on June 10, 2009, 04:50:18 pm
Post by: Ilovemathsmeth on June 10, 2009, 04:51:10 pm
Post by: leet on June 10, 2009, 04:56:51 pm
"Typical carrier gases include helium, nitrogen, argon, HYDROGEN and air."
but then:
"Safety and availability can also influence carrier selection, for example, hydrogen is flammable"
probably not the best source out there lol, but i guess the ideas are conflicting?
Post by: avram_grant on June 10, 2009, 04:58:46 pm
Post by: Lemollin on June 10, 2009, 04:59:31 pm
Post by: littlecherry25 on June 10, 2009, 05:00:55 pm
SHOULDN'T IT BE C???
4 different compounds can be formed......not 3??? MAO, have a look at it again
Post by: NE2000 on June 10, 2009, 05:03:19 pm
FOR MULTIPLE CHOICE QUESTION 12
SHOULDN'T IT BE C???
4 different compounds can be formed......not 3??? MAO, have a look at it again
http://vcenotes.com/forum/index.php/topic,14353.msg155765.html#msg155765
Post by: lukeperry91 on June 10, 2009, 05:07:12 pm
Post by: lukeperry91 on June 10, 2009, 05:11:54 pm
It only mentions hydrogen in passing in the detailed area on carrier gases. Hydrogen gas isn't listen in textbooks as a carrier gas. WTF
Post by: Ilovemathsmeth on June 10, 2009, 05:12:03 pm
Post by: huynhvien00 on June 10, 2009, 05:15:46 pm
http://pubs.acs.org/doi/abs/10.1021/ac50162a043
Post by: lukeperry91 on June 10, 2009, 05:18:59 pm
Post by: turley on June 10, 2009, 05:19:47 pm
realise the stuff we learn is really simplified down. As if your ever going to get a gas chromatogram with just one clear peak. Anyways, the reason inherts gases are used is so they don't react with the sample. However, i think the question deliberately mentions a "straight chain alkane" to test if we realise H2 gas doesn't react with it (or so says my chem text)
Post by: hard on June 10, 2009, 05:21:15 pm
Post by: turley on June 10, 2009, 05:22:45 pm
were assuming mao is right. vcaa could be doing drugs
Post by: lukeperry91 on June 10, 2009, 05:23:18 pm
Post by: Ilovemathsmeth on June 10, 2009, 05:24:05 pm
Post by: littlecherry25 on June 10, 2009, 05:24:13 pm
DOES NOT REACT WITH ALKANES.......
alkanes are unreactive...that's why you have to react them with Cl2 first before you can react them with NaOH
having said that...how much more will it NOT react with H2??
Post by: NE2000 on June 10, 2009, 05:26:01 pm
for the h2 gas multiple choice thingy
realise the stuff we learn is really simplified down. As if your ever going to get a gas chromatogram with just one clear peak. Anyways, the reason inherts gases are used is so they don't react with the sample. However, i think the question deliberately mentions a "straight chain alkane" to test if we realise H2 gas doesn't react with it (or so says my chem text)
They question may also have deliberately mentioned 'straight-chain alkane' so that we know that there are no polar groups to distort the order of boiling points we deduce. Anyway, it is all speculation at this stage, I think the only thing we have concluded was that it could go either way :)
Post by: lukeperry91 on June 10, 2009, 05:26:06 pm
Post by: turley on June 10, 2009, 05:30:49 pm
Post by: lukeperry91 on June 10, 2009, 05:35:16 pm
Post by: Mao on June 10, 2009, 05:37:10 pm
Mao would have got another 50 in the bag, change the rules VCAA!! And another in 2010 ..etc
It would be cool if you can repeat subjects, but unfair maybe. ;)
You can repeat subjects with no penalty, just takes longer time really.
Post by: Mao on June 10, 2009, 05:38:00 pm
hydrogen is highly flammable - so on that fact i didnt put hydrogen as it wouldnt be smart putting a flamable gas into a hot oven.... what do you guys think?Very interesting! Any thoughts Mao?
Flammable = combustion in oxygen. There's no oxygen in the column :P [but if they were oxygen containing hydrocarbons, it would indeed be dangerous]
H2 is otherwise unreactive for this situation. It may not be the best choice, but it certainly 'could have been used'
Post by: tomygun_123 on June 10, 2009, 05:41:57 pm
Post by: Mao on June 10, 2009, 05:43:02 pm
Post by: NE2000 on June 10, 2009, 05:43:25 pm
ey Mao, you sure about Qstn 14 of multiple choice?? id belive it to be C, the diagram is a bit tricky...
Sketch II represents an alpha helix: secondary structure
Post by: emo on June 10, 2009, 05:43:41 pm
Post by: homghomg1 on June 10, 2009, 05:44:25 pm
This is CO2 going to C6H12O6
The C goes from oxidation state +4 to 0, and this is therefore a reduction. unless there is something I am missing about "overall" reduction
Post by: NE2000 on June 10, 2009, 05:45:18 pm
any1 got the solutions
first post is Mao's solutions
Post by: Mao on June 10, 2009, 05:46:35 pm
ey Mao, you sure about Qstn 14 of multiple choice?? id belive it to be C, the diagram is a bit tricky...
tertiary structure is the overall shape of the protein due to interactions of Z groups. In this case, II is only interaction between the peptide linkages [which forms alpha helix or beta pleating], the over jumbled up structure in IV is the tertiary structure.
parts of IV are alpha helices, which are secondary structures, but the overall shape of IV shows the tertiary structure. :)
Post by: Mao on June 10, 2009, 05:48:23 pm
Hmm I haven't read through everything so maybe this has already been asked, but you didn't include Step 1 in the short answer Q7.Check Errata in first post :)
This is CO2 going to C6H12O6
The C goes from oxidation state +4 to 0, and this is therefore a reduction. unless there is something I am missing about "overall" reduction
Post by: ilovevce on June 10, 2009, 05:49:25 pm
Even if there were small amounts of oxygen or reactive impurities in the sample, combustion would not occur. If the volume concentration of H2 is greater than about 75%, uncontrolled combustion does not occur as there are simply not enough collisions between H2 and other molecules.
Post by: littlecherry25 on June 10, 2009, 05:53:46 pm
Post by: ilovevce on June 10, 2009, 05:54:54 pm
As for short answer Question 3 c (titration), I just realised I didn't read the question properly. Indeed the question did not specify whether NaOH was in the burette or conical flask. Check first post for additional explanation
Wouldn't it be convention that the HCl solution (with NaOH added) is in the burette? Usually the solution of unknown concentration is in the conical flask, and the solution of known concentration is in the burette.
Post by: eccentric on June 10, 2009, 05:56:57 pm
sigh ..... what you guys reckon the A+ cut off is ? i reckon its gonna be 63/73
Wasn't last year's cut off about 87% ?
Post by: homghomg1 on June 10, 2009, 05:58:24 pm
Hmm I haven't read through everything so maybe this has already been asked, but you didn't include Step 1 in the short answer Q7.Check Errata in first post :)
This is CO2 going to C6H12O6
The C goes from oxidation state +4 to 0, and this is therefore a reduction. unless there is something I am missing about "overall" reduction
Thanks, didn't see it. so we've concluded that Q19 is B and not D? If it's D I think I'm looking at 70/73
Post by: eccentric on June 10, 2009, 06:02:55 pm
Post by: Niksko on June 10, 2009, 06:03:09 pm
Post by: littlecherry25 on June 10, 2009, 06:06:07 pm
regarding MCQ 4, wouldn't the two OH groups count as an identical hydrogen environment because at this level we're taught to only take into account adjacent atoms when looking at whether a hydrogen environment is different, so therefore you would only get 3 sets of peaks?
there is only one OH group
the other group is a COOH group
Post by: homghomg1 on June 10, 2009, 06:21:36 pm
Hmm I only wrote about how salicylic acid and aspirin have different structures and will therefore have different retention times. I didn't put it together with the UV light information. I thought that was just to trick you, or maybe relevant to the next question and they put it there before for no reason. Count myself as losing 1 mark there. What Mao wrote was pretty smart, I doubt many people will be able to put the information together and come up with something similar. Hard question.
Post by: simpak on June 10, 2009, 06:24:23 pm
Short answer Q2 b)
Hmm I only wrote about how salicylic acid and aspirin have different structures and will therefore have different retention times. I didn't put it together with the UV light information. I thought that was just to trick you, or maybe relevant to the next question and they put it there before for no reason. Count myself as losing 1 mark there. What Mao wrote was pretty smart, I doubt many people will be able to put the information together and come up with something similar. Hard question.
I wrote about standards and calibration curves for concentration of salicylic in the product :)
Post by: TrueTears on June 10, 2009, 06:27:33 pm
Post by: spizaa #5 on June 10, 2009, 06:41:53 pm
Post by: simpak on June 10, 2009, 06:45:03 pm
I was confused.
I replaced a hydrogen from the CH3 with the Na and I have NO IDEA WHY.
This is what happens when you have to rush. Stupid length of exam booklet, you kill me.
Post by: homghomg1 on June 10, 2009, 06:49:44 pm
Showed all bonds except between O and Na. Instead i just had them together with no line --> ONa
I hope that's alright. I was considering writting a line in between them like in O-H.
I didn't because on the question they did not ask to show all bonds, as they usually do, and also they didn't even show the bonds between the OH in the original molecule themselves. I didn't wanna risk it cos I'm not sure if the Na acts like a H. I think it should be alright.
Post by: Mao on June 10, 2009, 06:54:22 pm
The two oxygens are 'resonance stablized', each having a bond order of 1.5 to the oxygen. It's similar to bonds in benzene.
As for what they actually accept, that is beyond my knowledge..
Post by: simpak on June 10, 2009, 06:55:55 pm
Barely anything said to show all bonds, only the first question, the ethanoic acid one and...did the zwitterion? I remember I drew all bonds for that.
Post by: nerd on June 10, 2009, 07:00:13 pm
Would this be OK?!
Post by: khalil on June 10, 2009, 07:00:30 pm
Post by: ming_mong on June 10, 2009, 07:01:01 pm
Post by: simpak on June 10, 2009, 07:02:40 pm
this exam doesn't look too bad. most students should have found it quite accessible.
It all looks sweet and peachy until you're asked to do it in 1.5 hours.
Post by: TrueTears on June 10, 2009, 07:03:06 pm
I didn't say anything about showing all bonds as far as I can recall.Question did say draw the COMPLETE structure, I guess that includes showing all bonds? :X
Barely anything said to show all bonds, only the first question, the ethanoic acid one and...did the zwitterion? I remember I drew all bonds for that.
Post by: khalil on June 10, 2009, 07:04:24 pm
never have i heard such tru wordsthis exam doesn't look too bad. most students should have found it quite accessible.
It all looks sweet and peachy until you're asked to do it in 1.5 hours.
Post by: BiG DaN on June 10, 2009, 07:04:38 pm
this exam doesn't look too bad. most students should have found it quite accessible.
It all looks sweet and peachy until you're asked to do it in 1.5 hours.
and when u get this
Methods - 50
Specialist Maths - 48
English - 45
Physics - 48
Chemistry - 49
Enhancement Maths - 5.5 increment
2007 ENTER : 99.95
Post by: khalil on June 10, 2009, 07:06:25 pm
i thought u had to get like 48-50 in english to get 99.95this exam doesn't look too bad. most students should have found it quite accessible.
It all looks sweet and peachy until you're asked to do it in 1.5 hours.
and when u get this
Methods - 50
Specialist Maths - 48
English - 45
Physics - 48
Chemistry - 49
Enhancement Maths - 5.5 increment
2007 ENTER : 99.95
Post by: TrueTears on June 10, 2009, 07:07:09 pm
45+i thought u had to get like 48-50 in english to get 99.95this exam doesn't look too bad. most students should have found it quite accessible.
It all looks sweet and peachy until you're asked to do it in 1.5 hours.
and when u get this
Methods - 50
Specialist Maths - 48
English - 45
Physics - 48
Chemistry - 49
Enhancement Maths - 5.5 increment
2007 ENTER : 99.95
Post by: Mao on June 10, 2009, 07:08:15 pm
this exam doesn't look too bad. most students should have found it quite accessible.
Accessible, yes. But to finish with confidence, hell no.
Post by: Mao on June 10, 2009, 07:09:11 pm
45+i thought u had to get like 48-50 in english to get 99.95this exam doesn't look too bad. most students should have found it quite accessible.
It all looks sweet and peachy until you're asked to do it in 1.5 hours.
and when u get this
Methods - 50
Specialist Maths - 48
English - 45
Physics - 48
Chemistry - 49
Enhancement Maths - 5.5 increment
2007 ENTER : 99.95
ENTER depends on sum of aggregate. Chances of 99.95 is greater if you have a fabulous English score, but otherwise not impossible.
Post by: simpak on June 10, 2009, 07:47:02 pm
Definitely focusing more on English from now on, then.
Post by: TrueTears on June 10, 2009, 07:51:26 pm
That makes me feel better about the ENTER I will need.There's no doubt if you want a good ENTER you must have good English SS. :\
Definitely focusing more on English from now on, then.
Post by: simpak on June 10, 2009, 07:53:01 pm
But I'm just saying I will pay it a little more attention now, I tend to let it slip a little bit because you can bullshit your way through it more than you can other subjects when you have a lot of assessments on.
Post by: hyperblade01 on June 10, 2009, 08:14:33 pm
Short Answer 9c)
5-bromouracil. Does the uracil in the name help with identifying it as thymine? Because when I saw it that's the first thing that popped into my mind :p
Edit: Jenny i know you're reading this :p
Post by: TrueTears on June 10, 2009, 08:15:13 pm
Just a little somethingUracil replaces Thymine in RNA.
Short Answer 9c)
5-bromouracil. Does the uracil in the name help with identifying it as thymine? Because when I saw it that's the first thing that popped into my mind :p
Edit: Jenny i know you're reading this :p
Post by: justin on June 10, 2009, 08:16:51 pm
Post by: hyperblade01 on June 10, 2009, 08:17:13 pm
Bio ftw :)
Edit:
Why was question 12 b) and not c)? Is it because you can't add elements in the middle section of a hydrocarbon?
The carbon in the middle is already bonded to 4 other carbons? Is that where you're talking bout?
Post by: simpak on June 10, 2009, 08:23:21 pm
Post by: ming_mong on June 10, 2009, 08:28:00 pm
if you had practiced enough, there should not have been any retarding force to prevent you from completing the exam with great prose.this exam doesn't look too bad. most students should have found it quite accessible.
Accessible, yes. But to finish with confidence, hell no.
Post by: simpak on June 10, 2009, 08:32:43 pm
if you had practiced enough, there should not have been any retarding force to prevent you from completing the exam with great prose.this exam doesn't look too bad. most students should have found it quite accessible.
Accessible, yes. But to finish with confidence, hell no.
Not tru fax!
I practiced more than I have ever practiced for anything in my life >.<
Post by: hyperblade01 on June 10, 2009, 08:33:36 pm
I don't entirely understand why it wasn't c, either.
The three methyl groups are one environment, the CH2 is another and the CH3 on the right is the third
Post by: simpak on June 10, 2009, 08:39:01 pm
It's probably because I didn't draw it out properly due to timing and I usually get confused by semistructural formula.
Post by: homghomg1 on June 10, 2009, 08:43:36 pm
this resulted in a 78.1% yield as opposed to 78.4%
it was a 4 part question, each worth 1 mark
do you think they will deduct marks for incorrect number of significant figures? If so, how many? Are there half marks in chem?
Post by: hyperblade01 on June 10, 2009, 08:44:06 pm
But yea, the 3 methyl groups , whichever one you place the Cl on the molecule is gonna be named the same
Post by: TrueTears on June 10, 2009, 08:44:36 pm
Hmm i just realised for Aspiring short answer question I rounder off too early. Got 0.016 as number of mol.Yes they do deduct marks for incorrect use of sig figs. 1 mark off the whole exam.
this resulted in a 78.1% yield as opposed to 78.4%
it was a 4 part question, each worth 1 mark
do you think they will deduct marks for incorrect number of significant figures? If so, how many? Are there half marks in chem?
Post by: simpak on June 10, 2009, 08:48:47 pm
Just realised maybe environment isnt the right word, too much NMR in my mind lol
But yea, the 3 methyl groups , whichever one you place the Cl on the molecule is gonna be named the same
But it shouldn't, should it?
If you put the chlorine on the first carbon, then it will be 1-choloro 2-dimethyl butane.
But if you put it on the 'last' carbon, then it will be 1-chloro 3-dimethyl butane?
If you put it on the carbon slotted in the middle, then it would be 2-chloro 3-methyl butane?
Or can you not put the chlorine on the methyl groups?
Argh I am probably missing something entirely. I never do too well with those sorts of questions.
Post by: hyperblade01 on June 10, 2009, 08:50:11 pm
Quote
Significant figures and states
Every paper has 1 mark for significant figures, and 1 mark for states. This means you can only lose 1 mark maximum, due to incorrectly doing your significant figures or states, but for those seeking to obtain these marks - don't fret. They only check one question to decide whether you pick up the mark or not. It is usually indicated by the question that says "express your answer to the appropriate number of significant figures" or "show all states." That will be the question they check for states, and they won't care about anything else, unless you state absurd amounts of significant figures.
Short Answer 3 b) stated give correct sig fig, so maybe you won't be penalised?
Post by: simpak on June 10, 2009, 08:51:17 pm
I hope it's okay.
Post by: mongyiu on June 10, 2009, 09:31:09 pm
Post by: simpak on June 10, 2009, 10:29:01 pm
Just realised maybe environment isnt the right word, too much NMR in my mind lol
But yea, the 3 methyl groups , whichever one you place the Cl on the molecule is gonna be named the same
But it shouldn't, should it?
If you put the chlorine on the first carbon, then it will be 1-choloro 2-dimethyl butane.
But if you put it on the 'last' carbon, then it will be 1-chloro 3-dimethyl butane?
If you put it on the carbon slotted in the middle, then it would be 2-chloro 3-methyl butane?
Or can you not put the chlorine on the methyl groups?
Argh I am probably missing something entirely. I never do too well with those sorts of questions.
Oh my god! I just got it, right then >.<
Oops! Nevermind.
Post by: Ilovemathsmeth on June 10, 2009, 11:46:09 pm
if you had practiced enough, there should not have been any retarding force to prevent you from completing the exam with great prose.this exam doesn't look too bad. most students should have found it quite accessible.
Accessible, yes. But to finish with confidence, hell no.
LOL a little hard under exam conditions, even if you had done about 30 practice exams...
Post by: tdavo23 on June 10, 2009, 11:47:37 pm
Put jellyfish in a bowl of acid and as it basic (place vinegar and the wound to neutalise sting) it should react with the acid.
The questions that i pose to you:
Would this be an acid-base reaction?
And secondly if yes What salt would be produced?
Post by: roly182 on June 11, 2009, 12:42:16 am
Post by: NE2000 on June 12, 2009, 10:15:58 am
Post by: ayaz on June 12, 2009, 09:30:19 pm
Post by: simpak on June 13, 2009, 09:49:18 pm
Post by: ericlambers on June 14, 2009, 03:09:17 pm
Post by: TrueTears on June 14, 2009, 03:12:30 pm
hi :DWrong place to post, introduce yourself here: http://vcenotes.com/forum/index.php/topic,6.555.html
Post by: lukeperry91 on June 15, 2009, 05:59:48 pm
hi :DWrong place to post, introduce yourself here: http://vcenotes.com/forum/index.php/topic,6.555.html
What a warm welcome.
Post by: Mao on June 15, 2009, 10:43:22 pm
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