Post by: Rosie on May 07, 2008, 02:26:30 pm
Write and equation showing the formation of the triglyceride glyceryl trioleate from the reaction of glycerol and oleic acid, CH3(CH2)7CH=CH(CH2)7COOH.
I wanted to know if my answer is correct.
CH4OCH4OCH4O + C17H33COOH ---> CH3(CH2)7CH=CH(CH2)7COOH + H2O
If it is correct, I'm not sure how to balance just because of the large numbers.
Post by: Collin Li on May 07, 2008, 02:57:20 pm
Here is a structural formula for glycerol:
Code: [Select]
H
|
H-C-OH
|
H-C-OH
|
H-C-OH
|
HIf you want an easier way to balance it, just write glycerol as its molecular formula:
However, I suspect this question wishes to see a structural formula. The three -OH groups on glycerol are sites for esterification. Simply draw the product of of a tri-esterification between 3 molecules of oleic acid, and 1 molecule of glycerol. The result will be three fatty acids on a glycerol molecule, hence the name: triglyceride. It looks like you've only done one esterification.
The molecular formula of the final product should be
However, it's not very easy to write a semi-structural formula for it, so I believe you've gotta actually do the structural formula.
This is how a generalised esterification occurs:
Code: [Select]
Z-OH + O=C-R ---> R-C=O
| |
OH O-ZYou should be able to use this to help you draw your triglyceride.
Post by: Mao on May 07, 2008, 04:02:58 pm
would they be (assuming this reaction carries out at body temperature - because this is where it takes place?):
*corrected*
are the states correct?
triolein will be a liquid because it cannot pack dense, right?
Post by: Collin Li on May 07, 2008, 04:16:26 pm
No idea what the triglyceride is.
Post by: Mao on May 07, 2008, 04:25:23 pm
i've looked up for triglyceride, their melting points are all different apparently, as the fatty acids differ, and if they are polyunsaturated, they have several bends and dont fit together nicely, etc.
for triolein, google says its melting point is around 4oC (some Wiley publication), so most probably a liquid.
though in the body, wouldnt there be emulsifiers (something or rather from the pancreas)?
In that case, would I still treat it as liquid? (or aqueous?)
and btw, OMG WIKIPEDIA ARTICLE ON "CHEMICAL EQUATIONS" SAYS NOTHING ABOUT STATES!!! =S
Post by: Rosie on May 26, 2008, 06:02:11 pm
I also don't understand how oxidants will always be reduced and reductants will always itself be oxidised.
Also wanted to know if ammonia is NH3 only and ammonium is NH4. Is this how you distinguish them?
Post by: Mao on May 26, 2008, 06:50:54 pm
and vice versa.
that's just what they are.
e.g. NH3, ammonia, is a base. It accepts a hydrogen, and becomes NH4+.
hence, NH3 and NH4+ are conjugates (a base and its conjugate acid)
same deal for acid-conjugate base
as for oxidant/reductant, thats the way they work.
an oxidant, such as oxygen, wants to gain electrons [strong electronegativity], and hence it reacts to gain negative charges, hence "reduced"
a reductant react with an oxidant [oxygen], and is "oxidised" [raped by oxygen]
and yes, thats the way you tell:
shorter length = less hydrogen.
ammonia -> ammonium
NH3 -> NH4+
Post by: polky on May 26, 2008, 07:16:02 pm
ammoNIA = 3 letters = NH3
ammoNIUM = 4 letters = NH4+ :D
Now I have to figure out a way of remembering that the reductant is the one that undergoes oxidation etc.
Post by: Mao on May 26, 2008, 08:12:49 pm
OILRIG
oxidation is loss, reduction is gain [of electrons]
and unit 4 specific [galvanic cells]
RedCat
reduction at cathode
Post by: cara.mel on May 27, 2008, 07:35:33 am
well, we do more redox next unit, but:
OILRIG
oxidation is loss, reduction is gain [of electrons]
and unit 4 specific [galvanic cells]
RedCat
reduction at cathode
The heinemann book at least combined them to 'an oil rig cat' (anode oxidation is loss reduction is gain cathode)
But yeah, in unit 1/2 my friend that wasn't continuing to 3/4 asked me for last minute important stuff to know so I said 'Reduction is gain' to him and that's it :D
Post by: Collin Li on May 28, 2008, 08:41:51 pm
Yeah!
ammoNIA = 3 letters = NH3
ammoNIUM = 4 letters = NH4+ :D
Now I have to figure out a way of remembering that the reductant is the one that undergoes oxidation etc.
The reductant is the thing that reduces the other species. Reduction and oxidation are always bound together (one does not happen without the other), so the reductant (which has reduced the other species) must have oxidised.
Post by: Rosie on June 02, 2008, 09:28:17 pm
Q. 1M solutions of several salts are prepared. Which of the following salts produces the solution with the highest pH?
A. Na2CO3
B. NaNO3
C. NH4Cl
D. Na2SO4
How do you know?
Q. Which of the following is a major component of biomass? (Firstly, what is biomass)
A. Natural gas
B. Ethanol
C. Cellulose
D. Crude Oil
thankyou everyone
Post by: Collin Li on June 02, 2008, 09:31:48 pm
Quote
Q. 1M solutions of several salts are prepared. Which of the following salts produces the solution with the highest pH?
A. Na2CO3
B. NaNO3
C. NH4Cl
D. Na2SO4
How do you know?
Eliminate the options which are not bases: NaNO3, NH4Cl, Na2SO4. How do I know these aren't bases? Recognise that these are ionic compounds, and look at each ion individually: the sodium ion is neutral, so is sulfate, chloride and nitrate. The ammonium ion is acidic. The only remaining option is sodium carbonate, a decent base.
Note: You will not be expected to compare the strength of bases. You should know, however, that inorganic acids are stronger than organic acids (in general - don't worry, they won't produce counterexamples unless it's irrelevant or they tell you about it)
Post by: Collin Li on June 02, 2008, 09:39:55 pm
Quote
Q. Propan-1-ol (M = 60g mol-1) undergoes complete fragmentation in a mass spectrometer. What is the m/e value of the base beak in its mass spectrum? I understand that the base peak is the largest peak in the spectrum and has an intensity of 100%.
This does not seem like a question you would be expected to know how to answer. My intuition tells me that it will be the isopropylium ion fragment, which has a molar mass of 43, but I would not expect you to have any idea why this is the case. The base peak has the greatest abundance because the base peak is the most stabilised fragment. I have used this basic idea to work it out, but it draws upon theory that is beyond the VCE course.
By the way, if you look at a lot of mass spectrums of organic molecules, the base peak is almost always 43. So if you do get an unfair question like this, just answer with that. For those who wish to understand why (out of curiosity), consider the stability of a fragment. A fragment requires a positive charge to be stabilised. It will certainly not include the electronegative oxygen, which depends on an abundance of negative charge. Here's a hint: alkyl groups are slightly electron donating. Not very, but still significant enough. Now, why did I pick isopropyl instead of just the plain propyl group?
I'm not actually sure if the isopropylium ion can form from this, but I'll just hope that it can. I don't know much about reactions with radicals, so I can't confirm whether this can be formed in the process of ionisation.
Quote
Q. Which of the following is a major component of biomass? (Firstly, what is biomass)
A. Natural gas
B. Ethanol
C. Cellulose
D. Crude Oil
From Wikipedia: Biomass refers to living and recently dead biological material that can be used as fuel or for industrial production. Most commonly, biomass refers to plant matter grown for use as biofuel, but it also includes plant or animal matter used for production of fibres, chemicals or heat.
I would pick cellulose - plant matter that will not get digested for energy by many living things, but can still be combusted for energy with some oxygen ;).
Post by: Mao on June 02, 2008, 09:56:58 pm
the answer, in this case, is actually CH2OH+, 31 m/zQuoteQ. Propan-1-ol (M = 60g mol-1) undergoes complete fragmentation in a mass spectrometer. What is the m/e value of the base beak in its mass spectrum? I understand that the base peak is the largest peak in the spectrum and has an intensity of 100%.
This does not seem like a question you would be expected to know how to answer. My intuition tells me that it will be the isopropylium ion fragment, which has a molar mass of 43, but I would not expect you to have any idea why this is the case. The base peak has the greatest abundance because the base peak is the most stabilised fragment. I have used this basic idea to work it out, but it draws upon theory that is beyond the VCE course.
By the way, if you look at a lot of mass spectrums of organic molecules, the base peak is almost always 43. So if you do get an unfair question like this, just answer with that. For those who wish to understand why (out of curiosity), consider the stability of a fragment. A fragment requires a positive charge to be stabilised. It will certainly not include the electronegative oxygen, which depends on an abundance of negative charge. Here's a hint: alkyl groups are slightly electron donating. Not very, but still significant enough. Now, why did I pick isopropyl instead of just the plain propyl group?
I'm not actually sure if the isopropylium ion can form from this, but I'll just hope that it can. I don't know much about reactions with radicals, so I can't confirm whether this can be formed in the process of ionisation.
it was in competition [amongst the choices] with CH3CH2+, which would be less abundant as it will further fragment down into CH3+
why? i have no clue :)
Post by: Rosie on June 05, 2008, 07:39:45 am
e.g. 5.09 * 10-2mol or 0.0509mol
Also, in the question(and for every question):
In order to determine the percentage, by mass, of water in an 850g can of soup, a student heats a 50.28g sample to dryness. After a number of heatings the mass of the residue on two successive weighings is 22.57g.
(a) Determine the percentage, by mass, of water in the soup.
When the answer is given, are you supposed to state your answer to 4 sig. figs not 3 because you are not using the 850g to get the answer for this question. So, does that mean only data you have used or manipulated to get your answer
Post by: Mao on June 05, 2008, 04:43:16 pm
If I had a question where I had to provide answer in 3 sig. figures, can you write it either way:both mean the same thing, so yes.
e.g. 5.09 * 10-2mol or 0.0509mol
Also, in the question(and for every question):significant figures are there to indicate *accuracy*, i.e. a less accurate number * more accurate number = not very accurate
In order to determine the percentage, by mass, of water in an 850g can of soup, a student heats a 50.28g sample to dryness. After a number of heatings the mass of the residue on two successive weighings is 22.57g.
(a) Determine the percentage, by mass, of water in the soup.
When the answer is given, are you supposed to state your answer to 4 sig. figs not 3 because you are not using the 850g to get the answer for this question. So, does that mean only data you have used or manipulated to get your answer
if all of the number you have worked with are accurate to four significant figures, then your answer is accurate to four significant figures
hence for this part you should retain four significant figures
it is likely that the second part asks you for the total amount in the 850g can, in which case you can only retain three significant figures
Post by: Rosie on June 06, 2008, 06:29:40 am