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OCR Chemistry A paper 1 (very) unofficial mark-scheme 14th June 2017 watch

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    12/3/18 Update: I, as per forum rules, will not be distributing the papers I acquired after my exams. However, if people sat them for a mock or otherwise attained them, and would like some worked examples I'd be more than happy to help if you send me a PM, granted I can find the papers when i return home from Uni at the end of this term (27/3/18).

    I've had a second look at the paper. here's a few of my answers (not in order):

    AlH4: 3 covalent bonds and one dative bond
    NH4+ - Tetrahedral, 109.5
    NH2- - non-linear, 104.5
    NH3>PH3 because H bonds. AsH3>PH3 as more E's so more dipole-dipole interactions so stronger London forces.
    Group 2 metals increase in reactivity as shielding increases, atomic radius increases, nuclear charge increase outweighed by inc. in radius and shielding so outer electrons less attracted by nucleus so easier to remove hence more reactive.

    Ba(NO3)2(aq) + Na2SO4(aq) -> BaSO4(s) + 2NaNO3(aq) | Entropy decreases as solid formed which is more ordered
    1/2 I2(s) -> I(g) | Entropy increases as gas formed which is less ordered/more disordered
    Acid/base pairs: CH3COOH(B2) + H2FCCOOH(A1) -> H2FCCOO-(B1) + CH3COOH2+(A2)
    Kp = p(CO)^4
    Kc = [SO3]^2/([SO2]^2[O2]) dm^3mol^-1, 2.45 mol so3

    pH = 4.50002 (this is right, 4.86 IS wrong.) pH is constant on dilution as [H+] = Ka ([HA]/[A-]) and conc's cancel out the volume.
    -110.5Kj/mol for Hf of CO
    690cm^3
    first order, rate at t=0: 1.84*10^-3, k=7.7-8*10^-4 units: s^-1 or per second (range of answers as from graph) halflife was about 900ish. graph had weird jumps so ppl might have messed up.
    962 Kelvin, 467KJ for at 25 degrees which > 0 hence not feasible.
    Disproportionation is when one species is both oxidised and reduced: Cl reduced from +5 to -1. Cl oxidised from +5 to +7.
    Potassium Chlorate(VII) [maybe they'll give potassium perchlorate but that isn't the systematic name afaik.]
    [Cu(H2O)6]2+ : with HCl = [CuCl4]2-, with dropwise NH3 = Cu(oh)2 with excess NH3 = [Cu(NH3)4(H2O)]2+ and with KI was I2(brown solution) and CuI(white ppt)
    named reactions for above: Ligand substitution and Redox.
    Free Energy question: y = mx + c : G = -S(T) + H, explain grad = -S, y int is c = H
    Le chatelier's principle: Forward reaction was endothermic so high temperature favors it, forward reaction was going to more moles of gas so a low pressure favors forward reaction. Actual conditions may vary as cost of maintaining high temperature and low pressure is high so a catalyst is used in favor of 'ideal' conditions.
    0.753 for something.
    Zn was best reducing agent, MnO4- was best oxidising

    https://gyazo.com/b77d7fda10b60699b9873d28a6417ff8
    All solutions 1mol/dm^3, 298K



    last question: DISCLAIMER: 'en' is NH2CH2CH2NH2 just wrote en for speed
    A = [Ni(en)3]cl2*2H2O
    B = [Ni(en)3]cl2
    C = [Ni(en)3]2+ - correct optical isomers drawn
    D = en = H2NCH2CH2NH2

    if you can remind me of any questions I might remember my answer. I know what I put for Multiple choice but not what letter they were.
    PS: these are not canon - they are MY answers.

    MY grade boundary predictions:
    89 - A*
    80 - A
    72 - B
    64 - C
    56 - E


    Topics to revise for paper 3:
    Born Haber
    Titration with I2/(S2O3)2- and MnO4-
    Arrhenius Equation/temperature effect on Kc
    Cation and Anion tests (Cr3+, Fe2+, Fe3+, Cu2+, Mn2+, NH4+ | CO32-, SO4^2-, Cl-, Br-. I-, order for anions is important!
    Relative reactivity of Halogens (Cl>Br>I)
    Enthalpy
    Boltzmann
    Calculating Kp from initial amounts + kp units
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    do you remember the marks for each question?
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    (Original post by eydalef)
    do you remember the marks for each question?
    Give me a question and i'll tell you what I think it was, not gonna be 100% sure though
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    Chromate or chlorate?
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    was it potassium chlorate (V) ? Would have only been a mark though if I messed this up
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    (Original post by numan1234)
    Chromate or chlorate?
    Chlorate. Thanks!
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    (Original post by maoism123)
    was it potassium chlorate (V) ? Would have only been a mark though if I messed this up
    (VII). They sneakily asked for the systematic name of KClO4!
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    (Original post by Toffo132)
    (VII). They sneakily asked for the systematic name of KClO4!
    Ahhh **** I thought it was KClO3, ah well should only be one mark right? I can't remember the question with 0.753 at all can you remember the numbers involved?
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    (Original post by maoism123)
    Ahhh **** I thought it was KClO3, ah well should only be one mark right? I can't remember the question with 0.753 at all can you remember the numbers involved?
    It was just one mark yes. I think it was concentration or moles of CH3COONa? something to do with that question.
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    (Original post by maoism123)
    was it potassium chlorate (V) ? Would have only been a mark though if I messed this up
    I put that too!
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    for the last one I wrote NH2C2H4NH2 in all my answers instead of NH2CH2CH2NH2, would I get a mark deducted for this?
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    (Original post by Toffo132)
    400ish for at 25 degrees which > 0 hence not feasible.
    I got 467K
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    (Original post by karunvsn)
    for the last one I wrote NH2C2H4NH2 in all my answers instead of NH2CH2CH2NH2, would I get a mark deducted for this?
    I'm not sure. it explicitly said show the structure, but I don't think you're chemically wrong in writing it like that. I personally would give you the BOD and mart it fully correct, but I'm not a marker nor a teacher.
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    Enthalpy of formation for (think it was CO?)

    -111 kJ mol^-1

    (given to 3sf because enthalpy change was only to this number of sf)
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    (Original post by Toffo132)
    It was just one mark yes. I think it was concentration or moles of CH3COONa? something to do with that question.
    I don't remember this question either. Do you remember other questions on this page? I feel like I've missed it out
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    (Original post by DoubleDoors)
    I got 467K
    For the temp at which feasibility changes it was:
    G=0 so rearranging gives: T = H/S
    T = (~674.3*1000)/(701) = 961.9=962K
    [THESE NUMBERS ARE ROUGHLY WHAT WAS GIVEN NOT EXACTLY!]
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    (Original post by Toffo132)
    For the temp at which feasibility changes it was:
    G=0 so rearranging gives: T = H/S
    T = (~674.3*1000)/(701) = 961.9=962K
    [THESE NUMBERS ARE ROUGHLY WHAT WAS GIVEN NOT EXACTLY!]
    I also got that

    I was referring to the question before it which asks you to show if feasible at 298K
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    For the hexaquacopper(II) question, what did you all put for the two types of reaction?

    I said:
    - Ligand Exchange
    - Precipitation
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    (Original post by DoubleDoors)
    I also got that

    I was referring to the question before it which asks you to show if feasible at 298K
    Ah. Yeah it was 400 and something, i'll put 467 though, thanks!
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    For the graph the letter marked as the X intercept was also the temperature at which the feasibility of the reaction changes (because y=g=0)
 
 
 
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