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

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    (Original post by four4)
    Do you think they'll award a mark for drawing the tripeptide as a repeat unit?
    No, because then it wouldn't be a tripeptide.
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    So what is the correct answer for PLA and stitches?
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    Does anyone have the exam paper?
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    inb4 57 for A*
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    (Original post by Raaaas)
    Plot twist, the answer to the first question is actually the second fatty acid...
    Thats what I wrote but Im not sure if its right...
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    for the question on the“Important” difference between chemical synthesis and fermentation, could you say fermentation is renewable but chemical synthesis isnt.
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    (Original post by lai812matthew)
    dilute hcl, nano2 not hno2.
    Hno2 is also accepted
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    (Original post by VMD100)
    The texbook (OCR) states on page 61 "Photodegradable polymers are initially coverted to waxy compounds when exposed to light, before being converted to carbon dioxide and water in the presence of bacteria"
    However I do not believe that this is the correct answer anyway. You are assuming that this is for external sutures and not internal. Poly (lactic acid) has a degradation time depending on presence of bacteria from around 47 days to 4+ years. An external stitch even at the shortest time of 47 days is far too long.

    The textbook on page 55 states "Poly (lactic acid) is biodegradable" I believe the marks are for explaining that the ester link is broken via hydrolysis due to the presence of water in both tissue and blood and that the third is for stating PLA is biodegradable and therefore breaks into carbon dioxide and water. Hence dissolvable stitches.
    only when the stitches are photodegradable they turn into carbon dioxide and water which they aren't.
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    (Original post by qhdop)
    So what is the correct answer for PLA and stitches?
    I would guess:
    Polylactic acid's ester group is hydrolysed, by H2O in the body (the blood plasma), into many monomers of lactic acid, which are soluble in H2O (blood plasma) due to their -OH and -COOH groups.
    As an extension or an "allow" mark, you may be able to say that lactic acid is broken down in the body/ metabolised.
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    (Original post by yiz)
    Do you think this is unambiguous enough for the mass spec fragment ion: H3CCH(NH2)+ ??

    Also other than saying the isoelectric point is the pH for the zwitterion, is it correct to say the zwitterion is "a dipolar ion with no overall charge" ?

    A reply would be much appreciated!!
    they won't mark the zwitterion part, but if they are asking about zwitterion, you are correct.
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    Does anybody have the grade boundries for the years for f324 and f325?

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    (Original post by Laurasaur)
    I would guess:
    Polylactic acid's ester group is hydrolysed, by H2O in the body (the blood plasma), into many monomers of lactic acid, which are soluble in H2O (blood plasma) due to their -OH and -COOH groups.
    As an extension or an "allow" mark, you may be able to say that lactic acid is broken down in the body/ metabolised.
    i have a very stupid question: lactic acid is liquid at rtp, so why would you need it to be soluble in H2O to let the stitches to dissolve.
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    How many marks for the stitches question?
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    (Original post by Manliker)
    Hno2 is also accepted
    if that is the case then HCl would have been accepted also without writing diluted. they just don't allow concentrated HCl.
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    (Original post by qhdop)
    How many marks for the stitches question?
    3 marks
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    For the TLC question could you put that there were 2 spots because two of the amino acids were the same?
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    if i said pla is biodegradable would I get a mark?
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    (Original post by lai812matthew)
    i have a very stupid question: lactic acid is liquid at rtp, so why would you need it to be soluble in H2O to let the stitches to dissolve.
    Ah, but define dissolve. You could have two liquids together that don't dissolve with each other, like if you put oil on water. Not a stupid question, I'm not 100% confident with my answer, but I'm mixing my chemistry and biology knowledge
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    would you not get a mark for saying fermentation is renewable but chemical synthesis isnt???
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    (Original post by lai812matthew)
    they won't mark the zwitterion part, but if they are asking about zwitterion, you are correct.
    Ok cool, and do you think the formula for my fragment ion is ok?
 
 
 
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