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AQA CHEM4 discussion/unofficial mark scheme Watch

  • View Poll Results: How hard did you find this paper?
    Easy, will get an A*
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    I flopped
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    (Original post by bessy.eia)
    me too!!
    I'm really worried now that I probs skipped the whole page.

    I just remember it asks about racemate

    and relationship of optical isomers

    -I also didn't see question on
    'state advantage of polyester over polyalkene' did you see this one coming up?
    That Q was why do you use PGA over polypropene in medical sutures?
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    (Original post by bessy.eia)
    me too!!
    I'm really worried now that I probs skipped the whole page.

    I just remember it asks about racemate

    and relationship of optical isomers

    -I also didn't see question on
    'state advantage of polyester over polyalkene' did you see this one coming up?
    okay, there was defo no question asking us to distinguish between racemate so not sure why it cropped up in the thread

    i think the 'polyester vs polyalkene' idea was the on of the questions about stitches paraphrased
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    I put aqueous KCN and then ammonia in excess??
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    (Original post by Jyotii)
    I feel ya! I put so much effort and was hoping for an A... as if that's happening now.
    Goodbye Uni!!
    Ah I really wanted an A* on this paper, and I was averaging that during past papers. But I honestly have never sat a worse exam, got thrown off completely. Not even sure if I'll get an A!


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    Im pretty sure there was no question on distinguishing between optical isomers?
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    (Original post by haj101)
    omg I put that too!! Thought I was the only one🙊🙊
    (Original post by lm98)
    Well that's exactly what I put so I really hope so!
    (Original post by penguinpenny)
    For question about P and Q, I put ethanol as the reagent. The acyl chloride gives sweet smell while the other doesn't. Do you think it would get the marks?
    I wrote this too, it made sense in the exam but is it legible
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    (Original post by yung7up)
    I wrote this too, it made sense in the exam but is it legible
    I don't know tbh
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    (Original post by chembiomaths28)
    I put aqueous KCN and then ammonia in excess??
    Yes i put that too but would it be right?
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    There was the question about ethanal and a diol (?) producing an acetal formula C4H8O2?
    It asked for the structure of the acetal?
    This is what I put anyways
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    (Original post by yung7up)
    Im pretty sure there was no question on distinguishing between optical isomers?
    Yeah i think you're right. The only one i recall along those lines was the "relationship between the two chiral molecules"

    I waffled about them being non-superimposable on one another.
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    (Original post by sim153)
    Yes i put that too but would it be right?
    I thought so, I can't remember what the question was exactly, but I thought it was KCN in aqueous conditions for that reaction and KOH in alcoholic conditions (so with ethanol) for a different reaction?
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    (Original post by chembiomaths28)
    I thought so, I can't remember what the question was exactly, but I thought it was KCN in aqueous conditions for that reaction and KOH in alcoholic conditions (so with ethanol) for a different reaction?
    Reagent: KCN
    Conditions: aqueous or alcoholic or aqueous ethanol

    Reagent: LiAlH4 or H2
    Conditions: ether or Ni catalyst
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    Do you think I might get a few marks for the last question if I stupidly did a tertiary alcohol but it still matched the infrared spectrum and proton NMR?I even wrote down has to be a primary or secondary alcohol- such a stupid mistake
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    (Original post by LearningGeek)
    Do you think I might get a few marks for the last question if I stupidly did a tertiary alcohol but it still matched the infrared spectrum and proton NMR?I even wrote down has to be a primary or secondary alcohol- such a stupid mistake
    I made the same mistake we should get marks hopefully for the peaks
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    (Original post by haj101)
    I made the same mistake we should get marks hopefully for the peaks
    Hopefully, I feel like a barely had enough time to check through my paper
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    Guys....was there a nucleophillic additon -elimination mechanism? I remember drawing one ?
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    (Original post by SubwayLover1)
    Guys....was there a nucleophillic additon -elimination mechanism? I remember drawing one ?
    Yup
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    (Original post by LearningGeek)
    Hopefully, I feel like a barely had enough time to check through my paper
    Me too! Really wanted an A in this :/
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    (Original post by logicmaryam)
    Heey guys, I think we can all agree this paper was one of the hardest CHEM4 papers ever.
    We'll discuss the answers and compile an unofficial mark scheme. Post your answers here!

    Predicted Grade boundaries by my friend
    90 RAW for full UMS maybe
    A* 82
    A 74
    B 66
    C 58

    Q1 20 marks
    a) Ethanoic acid in water
    CH3COOH ⇌ CH3COO- + H+ (1)
    b) Ethanoic acid as base with HNO3
    HNO3 + CH3COOH = CH3CHOOH2+ + NO3- (1)
    c) pH of acid? 2.08 (3)d) pH when alkali added to acid 2.32 (4)
    e) [salt]/[acid] = 3.33 (3) or 1.20?

    For the Kc - 9.09x10^3?
    k= 3.12x10-5 mol-1 dm3 s-1

    Q8
    Condition for step 1 (3)NaOH heat under reflux?
    use distillation or filtration to separate

    test for acyl chloride Q and some chlorohaloalkane P
    acidified AgNO3
    P - NVC
    Q - white ppt of AgCl Some people put H2O which would give fumes of HCl.

    Lidocaine 9 peaks is a or b more likely to be protonated, why?
    B because ethyl group is electron releasing so the lone electron pair on N is more available because benzene ring is withdrawing the pair at A.

    percentage mass of H = 9.4% because 22/233
    why isn’t Ka used in tables for strong acids? (2)
    Strong acids fully dissociates
    Ka = [H+]??
    Relationship between stereoisomers (1 or 2)
    mirror images and non-superimposable?

    Rate equation when propanone or something is increased
    rate = [H+]
    because propanone is in excess, H+ is limiting factor.

    Why is “X” zero order?
    not involved in the RDS and rate equation

    with knowledge of carbonyls, deduce name of mechanism
    haemacetol
    Nucleophilic addition

    2-Chloroethanoylchloride

    some other compound was 2-amino-4-methylpentanoic acid

    why is lidocaine hydrochloride used in medicine?
    More soluble as it forms stronger hydrogen bonds? the other one was polar too but lidocaine had N-H+

    Organic synthesis question (4)?
    KCN aqueous and ethanolHydrogen and Ni catalyst high pressure or LiAlH4 in ether

    orders of reaction (2)
    first, 1
    second, 2

    Why are “X” sutures used in medicine instead of polythene one? (2 or 3)
    Because X has polar bonds so is susceptible to attack by nucleophiles such as H2O in body so no need to remove it as it will break down over time. other one was non-polar

    Benzene one was just acylation
    electrophile CH3CO+
    [ClCH2COCl]+* -> [COCl+](37Cl) + [ClCH2*](35 Cl)

    Q9
    C6H1402

    61% Carbon
    11.9% Hydrogen
    27.1% Oxygen (100-11.9-61)

    my method:
    C : H : O
    0.61/12 0.119/1 0.271/16
    Then divide each answer by the answer of O to get C3H7O1 = Emperical. so X2 to get C6H14O2


    potassium dichromate turned green so must be primary or secondary HO-CH2-C(CH3)2-O-CH3??

    This one is by bluhbluhbluh
    Equation representing ethanoic acid as a base with nitric acid:

    CH3COOH + HNO3 -> CH3CO+NO3- + H2O

    Identify what reagents are needed to distinguish between the two chlorine molecules, incl. observation. (Acyl chloride vs haloalkane (?))
    Reagent: water/AgNO3 (?)/named carbonate
    Observation: HCl fumes/White ppt./Effervescence -for the acyl chloride.

    Which Nitrogen acts as a stronger base a vs. b (where a is attached to the benzene, and b is a tertiary amine) and why?
    Nitrogen b due to the positive inductive effect of the carbons on the nitrogen, therefore making the lone pairs more available. Consequently nitrogen a is joined to a benzene so the lone pair delocalises into the benzene ring.

    Order of reactions:
    D 1
    E 2

    What is a racemic mixture?
    Mixture containing equal quantities of each enantiomer.

    How to distinguish between the two:
    Expose to plane polarised light, rotates in opposite directions

    Chiral Carbon relationship:
    They are both mirror images of each other/enantiomers.

    4.
    Electrophile structure: CH3C(+)O

    Reaction mechanism:
    Arrow from benzene ring to C+ in CH3C(+)O, then arrow from hydrogen attached to the same carbon as the CH3CO back into the incomplete benzene ring (from carbon 1-4 i believe).

    5. Can't remember exact questions, let me know i'll update ! =)
    Notes:
    Zwitterions have R-N(+)H3 and a COO-
    Hydrogen bond between two amino acids: presumably show any partial bond from one hydrogen on one amino acid to either the nitrogen or oxygen on the other.
    Dipeptides- essentially amides formed from 2 amino acids.

    Advantage of using the polyester suture rather than the polyalkene?
    the ester bond in polyester can hydrolyse whereas polyalkene C-C, C-H bonds are too strong thus cannot. Therefore the former can dissolve naturally whereas the former would require manual removal.

    7. Conc. Of propanone increases by 100, What is the new rate equation and explain pls:
    rate = k[H+]Due to the large excess of propanone, it is no longer affecting the rate as only the H+ concentration limits the speed at which the reaction proceeds.

    Why is the initial rate of the reaction used to determine the order of the reactants rather than at any other point during the reaction? Or something
    Initial rate takes into account the initial concentration of the reactants which is more accurate since, as the reaction proceeds the concentrations of the different species change. (?)

    How do you calculate the initial rate of the reaction from a graph of concentration against time?
    Calculate the gradient of the tangent to the slope. (?)

    8. Organic synthesis to produce the branched primary amine:
    Structure: Same as previous however Br is substituted with CN
    Step 3: KCN w/ ethanol (?)
    Step 4: H2/Ni, LiAlH4

    Question 9 Notes
    Potassium dichromate turns green, either a primary or secondary alcohol, or aldehyde
    O-H absorption in the Mass spec
    O-H in NMR spectrum, singlet obvs
    CH3-O present in NMR spectrum, singlet
    RCH2 in NMR spectrum, triplet ?
    R(CH3)2 in NMR spectrum, doublet ?
    Hi, how did you find the paper easy? I mean wht will you get?
    2) How did you have access to the 2016 CHEM4 paper after you finished that? you claim tour answers are all right and no resit for the next year?
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    (Original post by haj101)
    Yup
    Thankyou so much!

    What other mechanisms were there?? I can't remember at all!
 
 
 
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