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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016) Watch

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    (Original post by h3rmit)
    If you get a U, probably not. Some teachers will allow those getting E's to pass through on a case by case basis. Revising is a better use of your time that worrying about your grades though
    give me some key topics to revise please i feel like im going to fail
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    (Original post by ineedhelpppl)
    give me some key topics to revise please i feel like im going to fail
    This is kind of what the practice papers you did in class (and the past and specimen papers you've been doing yourself) are for

    I'd recommend looking through the OCR specification and if anything there doesn't ring a bell, you need to revise it
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    If a 1 mark question was why does OH- ions act as a nucleophile? Is it because it's an electron pair donor


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    For one mark, that would be a good answer.

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    (Original post by Fish40)
    If a 1 mark question was why does OH- ions act as a nucleophile? Is it because it's an electron pair donor
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    Yes, correct.
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    Is there a mechanism we need to know for radical substitution? I know about initiation, propagation and termination but is there any curly arrows or anything we need to know??
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    (Original post by Clintbarton)
    Anyone got any predictions?


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    Definitely there will be questions on the different mechanisms; nucleophilic substitution, electrophilic addition and free-radical substitution needs to be known.

    Possible six markers can be based on a combination of different topics. It is difficult to predict 6 markers for chemistry. The practice paper had 6 markers on alcohols and dyanmic equilibrium which are good topics to be asked on. However, the practice paper may not look similar to actual papers...
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    (Original post by mollyayo)
    Is there a mechanism we need to know for radical substitution? I know about initiation, propagation and termination but is there any curly arrows or anything we need to know??
    Free radical substitution does not form curly arrows, they form radicals only.

    Electrophilic addition and nucleophilic substitution are the only mechanisms that involve curly arrows and any relevant dipoles.
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    (Original post by ineedhelpppl)
    give me some key topics to revise please i feel like im going to fail
    Different mechanisms:
    Free radical substitution
    Nucleophilic subsitution
    Electrophilic addition

    Dynamic equilibrium and working out the constant K
    Be confident applying calorimetry calculations
    Be condident working with mole questions, percentage yield, atom economy

    Alcohols, combustion general structure boiling points etc.
    Writing equations for alcohols (partial combustion ---> aldehyde, complete combustion ---> carboxylic acid)

    Tests for halide ions, carbonate ions, sulfate ions, ammonium ions
    Basic information about covalent bonding, ionic bonding and metalic bonding in terms of electrical conductivity, boiling points etc

    Ensuring that you know information about ozone depletion and writing the radicals for chlorofluorocarbon

    Boiling points, formation of bonds in alkanes and alkenes. Their basic structure, information etc.

    Mass spectrum

    Group 7 halogens (trends down a group, the bond that occurs between them, knowing the benefits and risks of chorine, knowing disproportional reaction)

    Uses for group 2 elements, trend down a group

    Ionisation energies.
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    (Original post by oni176)
    Free radical substitution does not form curly arrows, they form radicals only.

    Electrophilic addition and nucleophilic substitution are the only mechanisms that involve curly arrows and any relevant dipoles.
    Hahah Thankyou... Shows how much I know for my exam.
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    So do you get asked to do the mechanism for free radical substitution?? You don't do you, just the equations?


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    We should keep asking questions back and forth on this thread.


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    (Original post by Fish40)
    So do you get asked to do the mechanism for free radical substitution?? You don't do you, just the equations?


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    The equations are a mechanism
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    Yo please can I have some help with this question.
    Curing an experiment 11.50g of ethanol is completely burnt in air. During the combustion 341.5KJ of heat energy is released.
    What is the enthalpy change of combustion of ethanol?

    A) -341.5kjmol-1. B) -1366KJmol-1. C) -85.38KJmol-1. D) -34.15KJmol-1

    Cheers 😊
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    (Original post by harryleavey)
    The equations are a mechanism
    Do you ever have to draw the mechanism for free radical substituion? Or do you just get asked to write the equations?


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    (Original post by Farmerjj)
    Yo please can I have some help with this question.
    Curing an experiment 11.50g of ethanol is completely burnt in air. During the combustion 341.5KJ of heat energy is released.
    What is the enthalpy change of combustion of ethanol?

    A) -341.5kjmol-1. B) -1366KJmol-1. C) -85.38KJmol-1. D) -34.15KJmol-1

    Cheers 😊
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    (Original post by Fish40)
    Do you ever have to draw the mechanism for free radical substituion? Or do you just get asked to write the equations?


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    As I just said, the equations are a mechanism.
    If you are under the impression that there is a 'displayed mechanism' for free radical substitution reactions - there isn't one.

    I have attached a picture of the 3 mechanisms we need to know.
    I hope this helps

    Picture Credit: Revision Cards for OCR A Chemistry, RevisionTools.co.uk

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    (Original post by harryleavey)
    As I just said, the equations are a mechanism.
    If you are under the impression that there is a 'displayed mechanism' for free radical substitution reactions - there isn't one.

    I have attached a picture of the 3 mechanisms we need to know.
    I hope this helps

    Picture Credit: Revision Cards for OCR A Chemistry, RevisionTools.co.uk

    Thank you


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    Any questions your struggling with, post here


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    (Original post by Fish40)
    We should keep asking questions back and forth on this thread.


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    Good idea.

    The boiling points of three liquids, A, B and C are 65, 141, and 80 respectively. Liquid A reacts with liquid B to produce liquid C and water. Distillation of the reaction mixture produces four pure liquids, which are collected as they form in separate beakers. Which beaker (1st, 2nd, 3rd or 4th) would contain water?


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