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Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread watch

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    For the Ea thing it asked how to process the results so imo you did not need any experimental details.
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    (Original post by jess.olo)
    I thought this too! but people are saying it was quite nice! what do you think the grade boundary for A* will be!?
    I don't know :s I hope the grade boundaries will be low!
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    (Original post by C0balt)
    Yes
    Ah Thanks
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    That exam was soo disgusting

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    (Original post by C0balt)
    For the Ea thing it asked how to process the results so imo you did not need any experimental details.
    Gonna agree with you there partly because I agree and partly because I didn't write any experimental details so if we were supposed to then I'm screwed x 2.

    Lol.
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    I'm confused with what people are saying about ester hydrolysis and ester FORMATION (compound D as opposed to salicylic acid)

    for the Compound D (acyl chloride) compared to using an acid to make the ester I said:
    - Irreversible
    - Forms HCl instead of Water
    - Does not need catalyst

    For the acid/base hydrolysis
    - Base forms salt/carboxylate ion
    - Base hydrolysis is faster
    - Greater yield of ester (I ran out of ideas !????)
    ^ but my revision guide is actually telling me that BOTH acid and base hydrolysis are reversible and no HCl is formed because you're hydrolysing. I think people are getting mixed up!?
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    It was 4.03 was it not?
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    (Original post by CLGC98)
    It was 4.03 was it not?
    yep.
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    Are we allowed to create unofficial mark schemes?
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    Some answers I remember putting down:

    Multiple choice
    - decrease both pressure and temperature for more NO yield
    - Propane 1-2-3 triol
    - hexane at top with higher iodine conc.
    - only one of the addition leads to elimination (can't be chiral as no chiral carbon)

    H2S Qs
    - HS- was something x10^-5
    - pH was 4 something (4.02?)
    - assumptions: water does not dissociate to make any H+, [H2S]eq = initial conc., second ionisation is negligible due to tiny Ka

    Titration curve
    - 2 equivalence points, first one's half equivalent point is at 1.9, the other at 7.2, end point has pH of 13
    - to work out pKa1 look for pH at first half equivalence point

    Rate stuff
    -Br- was first order as proportional change to 1/t (which is proportional to initial rate) as Br- changes
    - units for rate constant I said mol^-3dm^9s^-1

    Clock reaction- for why phenol was in small conc. I said 1/t proportional to rate is only valid if less than 10-15% of the acid is used up etc
    - can't remember the questions, if someone can tell me I'll remember my answers

    Iodine clock test
    - solution turns blue black as thiosulfate is used up
    - that horrible 6 marker (I think I screwed up royally), I said first repeat experiments with all reactants but one at excess conc., then do so with other reactants, to work out orders with respect to them etc. then you can work out k via rate equation, then repeat reaction at various temperatures to get your various k and T values, then plot lnk vs 1/T graph then multiply the gradient by -R to get Ea

    Section C
    - products of alkaline hydrolysis were salicylate salt and methanol
    - difference between D and salicylic acids reaction with ethanol is D occurs a lot quicker and doesn't need conc. strong acid catalyst, and is non reversible
    -reagents were PCl5 and LiAlH4, skeletal formula was of ethyl salicylate
    -differences between acid and alkaline hydrolysis: one forms a salt and alcohol the other a carboxylic acid and alcohol, one is reversible (acid) the other isn't, alkaline requires one more step (protonation via dilute strong acid) to make carboxylate acid

    NMR
    - 3 peaks, a quartet a triplet and a singlet
    - 3-2-1 ratio
    - if I remember right, at 1, 2.5 and 3.5 ppm or something like that


    -I'll remember more answers if im reminded of the questions


    Much harder than past papers I thought :/
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    (Original post by Don Pedro K.)
    yep.
    I think anywhere in the 4 range would suffice
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    (Original post by Don Pedro K.)
    yep.
    What was the assumptions you made then? Because I got 4.03 but then I doubted myself and changed it to 4.25 assuming that the concentration of H2S and H20 was the same
    • Welcome Squad
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    Welcome Squad
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    Just thought I'd pop this here

    The specification clearly mentioned that we only need to be aware of different combinations of MONOPROTIC acid/base titrations
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    (Original post by tayloryeah)
    What was the assumptions you made then? Because I got 4.03 but then I doubted myself and changed it to 4.25 assuming that the concentration of H2S and H20 was the same
    I said that the dissociation of water is negligible, the dissociation of the weak acid is negligible and that all the H+ comes from the acid. I'm sure about the last two but I think for the first one I may have had to say that H+ ions from water is neglible. Actually I think I did put that o.O I can't remember XD
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    Imho the paper wasn't outrageously difficult but it was definitely on slightly more difficult side. No one question was impossible but there were a few dodgy ones like diprotic titration curve, detailed questions on hydrolysis (which never happened afaik), drawing NMR spectrum, asking about volume of phenol etc.. People wouldn't have lost entire 6 marks or 3 marks or whatever but majority will have lost quite a few here and there to cumulate a slightly low total mark...
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    Does anyone reneber what they wrote for the two ka expressions?
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    Was it ok to draw the titration curve and nmr in pencil?
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    (Original post by feraligatr)
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    just thought i'd pop this here

    the specification clearly mentioned that we only need to be aware of different combinations of monoprotic acid/base titrations
    they went against their own spec??????????
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    (Original post by Don Pedro K.)
    I said that the dissociation of water is negligible, the dissociation of the weak acid is negligible and that all the H+ comes from the acid. I'm sure about the last two but I think for the first one I may have had to say that H+ ions from water is neglible. Actually I think I did put that o.O I can't remember XD
    1 and 3 are the same thing
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    I forgot to add integration traces to my NMR spectrum but I did write about how tall each peak was related to the others in the discussion. Is that fine?
    ---
    And for the 2nd acid base question (to find the equilibrium conc of acid), where you meant to find the concentration of H and take it away from 0.1 (initial conc of acid)? I got something like 0.0999 for that question and it just seems sooo wrong.
 
 
 
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