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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???
    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.
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    (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-resourc...stions-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.
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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???

    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?
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    (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.
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    (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
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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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    (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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    (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.
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    (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/Exa...additional.htm

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    Thanks so much!
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    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?
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    (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
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    (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.
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    (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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    (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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    That makes sense thankyou! I was so confused cos my teacher actually told us to protonate/deprotonate all groups :/
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    (Original post by ToLiveInADream)
    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.
    Thank you v much
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    Hiya, was looking to see if anyone has the June 15 F324 and F325 Papers and Mark Schemes!! I'll be very grateful since i'm sitting externally so don't have access to them ¬_¬
    Thanks in advance !
 
 
 
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