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OCR Chemistry A - AS in Depth - 2015 (new spec) UNOFFICIAL MARK SCHEME Watch

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    What did everyone get for the structure of C for the last question?
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    Idk how that C-O-H question was worth 4 marks

    104.5 (1)
    2 bond pairs, 2 lone pairs (1)
    Lone pair repels more than bond pair (1)

    Then I put it should be 109.5 if it was bond pair but each lone pair reduces the angle by 2.5, so the 2 lone pairs 109.5-5=104.5
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    2-methylpropanoic acid my g
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    What do we think grade boundaries will be? And are they using UMS?
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    grade bounderies?
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    (Original post by alkaline.)
    okay ill put what i can remember in terms of workings spoilers - I can't remember everything lol I'll try
    also I don't remember what numbers each question was but I've tried to group them into colour schemes for whole questions

    if you remember anything additional please do say and I'll edit it in.
    I don't think you need to go to the trouble of writing all these calculations out! That user obviously hasn't done the AS exam and his/ her school is probably using the exam we did today as a mock for their predicted grades. So upload if you don't care about that, I just wanted to warn you as OCR do want their papers secure and not leaked.
    Answers are still gonna spill out, it's just that you shouldn't feel obliged to write out all the calculations, you get me?

    Hope the exam went well for you! I'm noticing all these silly errors I made :/
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    (Original post by neek101)
    What did everyone get for the structure of C for the last question?
    I got it wrong but the right answer was 2-methylpropanoic acid
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    (Original post by simply_a_ Δ)
    I don't think you need to go to the trouble of writing all these calculations out! That user obviously hasn't done the AS exam and his/ her school is probably using the exam we did today as a mock for their predicted grades. So upload if you don't care about that, I just wanted to warn you as OCR do want their papers secure and not leaked.
    Answers are still gonna spill out, it's just that you shouldn't feel obliged to write out all the calculations, you get me?

    Hope the exam went well for you! I'm noticing all these silly errors I made :/
    oh crap what?
    ppl make these threads all the time though if im violating the law ppl tell me cause I don't wanna get nullified as levels...
    yeah I cba to put the calculations lol

    thank you I think it went okay, I also made stupid errors dw
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    For the draw the diagram for the equipment and experiment, instead of a gas syringe I did a measuring cylinder in a tray of water cos thats how we did it in class?
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    (Original post by alkaline.)
    oh crap what?
    ppl make these threads all the time though if im violating the law ppl tell me cause I don't wanna get nullified as levels...
    yeah I cba to put the calculations lol

    thank you I think it went okay, I also made stupid errors dw
    no don't worry, you won't get disqualified! It's just that ocr may ask you to take this down. Don't worry, the a level chemsitry teacher who posted his answers to the breadth paper also just got told to delete it, he didn't get sacked haha!
    OCR know that their papers will get leaked so they can't really do much to control it, so it's just up to us to respect their wishes
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    (Original post by 4nonymous)
    For the draw the diagram for the equipment and experiment, instead of a gas syringe I did a measuring cylinder in a tray of water cos thats how we did it in class?
    That's what was written in the Biology textbook so is valid but the Chemistry textbook says you should use a gas syringe so :dontknow:
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    (Original post by simply_a_ Δ)
    no don't worry, you won't get disqualified! It's just that ocr may ask you to take this down. Don't worry, the a level chemsitry teacher who posted his answers to the breadth paper also just got told to delete it, he didn't get sacked haha!
    OCR know that their papers will get leaked so they can't really do much to control it, so it's just up to us to respect their wishes
    I understand, I mean I just wanted to discuss the answers I'm not trying to leak the papers lol
    plus they were really annoying this year they didn't even post the answers to the practise questions until some weeks before the exams?!

    anyway i don't get what the big deal is they'll release the papers next year anyway? what's leaking really
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    There is no such thing as 2-methylpropanoic acid. The compound is methylpropanoic acid.
    If the stem is 'prop', any alkyl groups must be attached to the second carbon atom- otherwise the stem changes to 'but'.
    The '2' is therefore redundant.

    (Not sure if marks will be docked for this.)
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    The question about the graph, was describe and explain the rate of reaction. If the mass was decreasing surly the rate of reaction was increasing?
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    Yeah that's what I thought too!
    (Original post by Tom malikk)
    The question about the graph, was describe and explain the rate of reaction. If the mass was decreasing surly the rate of reaction was increasing?
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    why is this apparatus not suitable for oxidising a secondary alcohol?

    Its because some of the reactants are volatile so may evaporate before reacting, which is why you need to use reflux apparatus.
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    (Original post by alkaline.)
    yo we don't have one yet.
    this is what I remember pls feel free to correct and also add missed questions.
    the colour scheme is to try and separate whole questions.

    draw the apparatus you'd use:
    I put a clamp stand with a syringe on the left, and a clamp stand holding a test tube with metal and water in with the bung connected to the syringe.
    OR



    the unknown metal: calcium

    percentage yield: 67.4%

    explain oxidation of magnesium in terms of electrons (1 mark)
    oxidation of magnesium is loss of two electrons.

    electron configuration of a magnesium atom
    1s2 2s2 2p6 3s2

    Magnesium vs Silicon
    Magnesium = giant metallic, metallically bonded = electrostatic attraction between negatively charged delocalised sea of electrons and positively charged Mg ions.

    Silicon = giant molecular, covalently bonded (electrostatic attraction between shared pairs of electron and the nuclei of bonding atoms), forming a lattice.

    the difference in melting point - p4 and cl2 - on the graph chlorine was lower
    I put: they are both covalently bonded, butchlorine is a smaller molecule, and so has weaker london forces therefore less energy is required to break the intermolecular forces therefore lower melting point.

    second ionisation energy for strontium inc state symbols
    Sr+ (g) --> Sr2+ (g) + e-

    a question to do with explaining ionisation energy trend down group 2 but I can't remember btwn which elements
    nuclear charge increases down the group however this is outweighed by increase in shielding and also increase in atomic radius, therefore there is less nuclear attraction (between nucleus and outer electrons) so outer electrons are more easily lost/less energy is required to remove them therefore lower first ionisation energy.

    mass of strontium carbonate = 1.845g

    rates question: why was there loss in mass or something?
    I put cause the reactants were getting used up and (2 mol of gas given off)

    describe and explain the trend in the graph up to 200s.
    mass rapidly decreases as time goes on = high ROR

    explain why enthalpy change of formation for NO was exothermic in terms of bonds
    I put because more bonds made than were broken and making bonds releases energy whereas bond breaking uses up energy.

    enthalpy profile diagram: endothermic
    bottom left = reactants = N2 + 0.5 O2
    top right = products = n20

    pv=nrt question: (in standard form) 4.46*10^6 Pa
    show NO catalyses the break down of ozone:NO• + O3 -> NO2• + O2NO2• + O -> NO• + O2

    mechanism for the reaction of compound A an alkene with a hydrogen halide (HBr)
    show the mechanism, the two different products, explain which of two would form more of.

    unsymmetrical alkene CH3HC=CCH3CH3 , basically the second possible product just had the H and Br on the resulting haloalkane switched around, more of the tertiary halogenoalkane would be formed because it's more stable.

    why can't compound A (alkene) exhibit E/Z isomerism?
    because it doesn't have 2 different groups on each carbon of the double bond.

    Z isomer for the alkene:
    Z pent-2-ene

    structural isomers: 2 methyl 2 butan-2-ol and 3 methyl butan-2-ol

    why is it a secondary carbocation?
    because the halogen is attached to the carbon that is attached to 2 alkyl groups

    write equation for butan-2-ol oxidising
    I drew out: butan-2-ol + [O] - butanone + h20

    bond angle around the oxygen in the butan-2-ol (3 marks)
    104.5
    reason: 2 bonding pairs and 2 lone pairs around the central atom, electron pairs repel to maximum separation = non-linear shape.
    Spoiler:
    Show
    I personally think: 4 electron regions = tetrahedral = 109.5, but then 2 lone pair so 109.5 - ( 2 x 2.5) = 104.5 is also acceptable part of the answer.
    why is this apparatus not suitable for oxidising a secondary alcohol?
    i didn’t know this but I put: because nowhere to separately collect the products, reflux apparatus would be better.

    aluminium sulfide and water forming aluminium nitrate and hydrogen sulfide
    Al2S3 + 6H2O -> 2Al(OH)3 + 3 H2S

    last question (mass spectrum/ infrared red) conspiracy as it currently stands = methylpropanoic acid


    Another question was that if the group 2 metal was replaced with another one further down group in the reaction with the acid, will the volume increase, decrease or stay the same? I put it will decrease because the molar mass would increase and so the moles would decrease causing the volume to decrease.

    There was another part of the question above this asking what group 2 metal is reacting, I got calcium.
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    (Original post by Alishajani10)
    Yeah that's what I thought too!
    (Original post by Tom malikk)
    The question about the graph, was describe and explain the rate of reaction. If the mass was decreasing surly the rate of reaction was increasing?
    In the first few seconds the rate of reaction is fastest due to presence of the a lot of reactants. However rate of reaction decrease as the reactants get used up and less reactants are left to react (less Likely collision)

    Value is negative because mass is decreasing so the graph goes downwards. This means the gradient will be negative.

    Sorry I'm not the best at explaining but I've tried
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    (Original post by alkaline.)
    I understand, I mean I just wanted to discuss the answers I'm not trying to leak the papers lol
    plus they were really annoying this year they didn't even post the answers to the practise questions until some weeks before the exams?!

    anyway i don't get what the big deal is they'll release the papers next year anyway? what's leaking really
    Yes at the end of the day it doesn't matter
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    I used the syringe method too! I hope its ok to do so.
    (Original post by alkaline.)
    thanks everyone for contributions so far!



    also that first diagram I swear they said they wanted to measure the volume that's why I put a syringe, originally I had put the image you've posted :/


    I said really similar like
    weigh the beaker, add the acid weigh again, weigh oxide and add it, start stopwatch as soon as you add the oxide
    i didn't say specifically measure the mass of src03 because the graph was (regants + container)
    except i said record reading on the scale every 10 seconds
    I think I was wrong too though.
 
 
 
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