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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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Hey guys on the f324 papers I've got an A* on every one apart from the 2015 one in which I got a C :/, do you think it'll be as hard as 2015 and if so what can I do now to get even better? I've done the past papers nearly twice
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AqsaMx
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With zwitterions, if there is a COOH/NH2 group on the R group, you don't protonate/deprotonate it?

my teachers been teaching us that you do but on a ms, I saw only one NH2 being protonated? Can anyone explain this pls???
Original post by HarveySpecter97
Hey guys on the f324 papers I've got an A* on every one apart from the 2015 one in which I got a C :/, do you think it'll be as hard as 2015 and if so what can I do now to get even better? I've done the past papers nearly twice


The 2015 paper wasn't that hard for me, I just thought there were too many questions to do within the time limit.

Have you tried the legacy papers?
Original post by AqsaMx
With zwitterions, if there is a COOH/NH2 group on the R group, you don't protonate/deprotonate it?

my teachers been teaching us that you do but on a ms, I saw only one NH2 being protonated? Can anyone explain this pls???


Zwitterions you only do 1 group each, it doesn't matter where from (could be the R group COOH/NH2 or the normal groups) but the key thing is once. For when acids are above or below their zwitterion pH point (isoelectric point) is where ALL groups are protonated/deprotanated.
(edited 7 years ago)
Original post by HarveySpecter97
Hey guys on the f324 papers I've got an A* on every one apart from the 2015 one in which I got a C :/, do you think it'll be as hard as 2015 and if so what can I do now to get even better? I've done the past papers nearly twice


Its definitely gonna be that hard. In 2013 the exam board got reviewed and they complained that the chemistry exams are too predictable and there are too many people getting high marks so they are mixing it up a bit. The only papers that are gonna be any reflection of what its gonna be like this year are June 14 and 15.

Don't panic. Look at reaction mechanisms that aren't on the specification but count as application of knowledge.Just check you understand them. If it comes up then you've already seen it and you can reel them off.
http://www.chemguide.co.uk/mechmenu.html#top

Look at these NMR Qs
Particularly the hardest ones.
https://www.tes.com/teaching-resource/ocr-chemistry-f324-module-3-nmr-practice-questions-6259747

maybe mess around with spectrum simulator at http://www.nmrdb.org/ Draw in a compound and test whether you can guess the number and position of peaks of h and C13 before you look. I think it's gonna be an alkene or an amide this year(maybe even a triglyceride or an azo dye). Everything else has come up.

Also, there are little tidbits in the book that might get examined. Like shorthand notation of fatty acids. Why substitution occurs and addition doesn't in benzene rings. Bonding in carbonyls. Basically, anything you haven't seen before is likely to come up as its last year of examination on this spec.

Hope that helps.
Original post by AqsaMx
With zwitterions, if there is a COOH/NH2 group on the R group, you don't protonate/deprotonate it?

my teachers been teaching us that you do but on a ms, I saw only one NH2 being protonated? Can anyone explain this pls???



Without seeing the question, I'm assuming it's because the amino acid has only one carboxylic acid group but multiple amino groups. Knowing that when an amino acid forms a zwitterion, the carboxylic acid group donates a proton to the amino group, if there is more amino groups than carboxylic acid groups, the amino acid can't self protonate all of its amino groups.
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Original post by rory58824
The 2015 paper wasn't that hard for me, I just thought there were too many questions to do within the time limit.

Have you tried the legacy papers?


No, is it all the same stuff?
Original post by HarveySpecter97
No, is it all the same stuff?


Yes, mostly. There was a post in this thread with a link to all of the older papers, with questions crossed out which aren't part of this specification.
Original post by rory58824
Yes, mostly. There was a post in this thread with a link to all of the older papers, with questions crossed out which aren't part of this specification.


Yeah okay thanks; I'll try and sieve through the thread to find the link
Reply 709
Avatar for ranz
ranz
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Original post by AqsaMx
With zwitterions, if there is a COOH/NH2 group on the R group, you don't protonate/deprotonate it?

my teachers been teaching us that you do but on a ms, I saw only one NH2 being protonated? Can anyone explain this pls???


thats exactly my qs


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Reply 710
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ranz
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Original post by Serine Soul
All amines (if they can, i.e primary or secondary amines) accept a H+ ion in acid hydrolysis (lone pair of e- on N atom) as there is an abundance of H+ ions, supplied by the acid

Similarly, all carboxylic acid groups become carboxylate ions and form a salt in alkali hydrolysis.
So all COOHs turn into COO-Na+ with NaOH


what if there was an OH present along with a carboxylic acid group, would the OH also form O-Na+?


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Reply 711
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ranz
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Original post by pineneedles
Without seeing the question, I'm assuming it's because the amino acid has only one carboxylic acid group but multiple amino groups. Knowing that when an amino acid forms a zwitterion, the carboxylic acid group donates a proton to the amino group, if there is more amino groups than carboxylic acid groups, the amino acid can't self protonate all of its amino groups.
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so lets say there were 2 amino groups and 2 carboxylic acids would they both protonate in a zwitterion?


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Original post by ranz
what if there was an OH present along with a carboxylic acid group, would the OH also form O-Na+?


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Like an alcohol on one end and carboxylic acid on the other?

Alcohols, except phenol, aren't acidic enough to form a salt.
Original post by ranz
so lets say there were 2 amino groups and 2 carboxylic acids would they both protonate in a zwitterion?


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Yes, I'm sure they would

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Original post by HarveySpecter97
Yeah okay thanks; I'll try and sieve through the thread to find the link


Here, I have the link saved:

http://www.chemhume.co.uk/A2CHEM/ExamsMSA2/ExamMSA2%20additional.htm

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Original post by pineneedles


Thanks so much! :smile:
Do hydogen bonds form between water molecules and the c=o on the carboxylic acid? How would this compare to the conventional hydrogen bonding between o-h groups and water molecules?
Original post by pineneedles
Yes, I'm sure they would

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At their isoelectric point, which is where the amino acids exists as a zwitterion, the charge has to neutral as the proton from the carboxylic acid is donated to the amine group, despite if there is another amine or carboxylic acid group on the R group

If the amino acid had an R group with another amine group, at a pH lower than its isoelectric point (more H+), the amine group would accept a proton

If the amino acid had an R group with another carboxylic acid group, at a pH higher than its isoelectric point (more OH-) the carboxylic acid would lose a proton
Original post by dash52
Do hydogen bonds form between water molecules and the c=o on the carboxylic acid? How would this compare to the conventional hydrogen bonding between o-h groups and water molecules?


Hydrogens bonds wouldn't form as the only form hydrogen and flourine or hydrogen and oxygen and hydrogen and nitrogen. I'm pretty sure anyway.
Original post by dash52
Do hydogen bonds form between water molecules and the c=o on the carboxylic acid? How would this compare to the conventional hydrogen bonding between o-h groups and water molecules?


Both the C=O and O-H groups can form hydrogen bonds with water. It is the same concept as the conventional hydrogen bonding (and remember your dipoles!)

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