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    (Original post by AffirmedCube)
    Basic organic chemistry, nucleophilic substitution of Br with OH, followed by reprotonation of the O- to OH by addition of a strong acid. I believe this is discussed a few pages back in the thread.
    Dammit do you know what AS stuff we need for this?
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    (Original post by thymolphthalein)
    IAL Jan 2015 had a 3 mark question for briefly describing the steps for determining purity by recrystallization. It did not ask for details though.
    For that you just need to say add 2,4-DNPH and filter, then recrystallise to get the pure solid, and then measure the melting temperature and compare it to known values in a data book


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    Why is 14aiii 20cm3?

    http://qualifications.pearson.com/co...e_20120613.pdf
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    (Original post by Nautic4l)
    Dammit do you know what AS stuff we need for this?
    You must know SN1 and SN2 (nucleophilic substitution) and how it links to rates, and which one forms a racemic mixture (SN1) vs. a single enantiomer (SN2)! Good luck
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    (Original post by ArielHaeems)
    partial pressure = mole fraction x total pressure

    rearranging this, mole fraction = partial pressure / total pressure

    so mole fraction does decrease if total pressure increases..?
    thats what i thought
    but on the jan 2010 paper, the answer for number 1 is B:/
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    (Original post by rowanbarnesss)
    For that you just need to say add 2,4-DNPH and filter, then recrystallise to get the pure solid, and then measure the melting temperature and compare it to known values in a data book


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    Yes, I know. I sat for that paper.
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    Firstly, its 1 mark, so you know it will not require any calculations (this does not apply to MCQs).
    The end point is when the no. of moles of acid and base are equal, so because they have the same concentration and the alkali is in excess, it is 20cm3.
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    (Original post by AffirmedCube)
    You must know SN1 and SN2 (nucleophilic substitution) and how it links to rates, and which one forms a racemic mixture (SN1) vs. a single enantiomer (SN2)! Good luck
    Ah okay thank you Nothing else yeah? Basic organic chem?
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    What's better HPLC or low resolution?



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    (Original post by Nautic4l)
    Dammit do you know what AS stuff we need for this?
    Helps if you remember most of the basic organic chemistry. I've also seen a question regarding E-Z isomers in an IAL paper.

    Heterogeneous/Homogeneous catalysts might come up for a few marks with a rate question.

    AS mechanisms are important as well.
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    (Original post by Nautic4l)
    Ah okay thank you Nothing else yeah? Basic organic chem?
    Because the paper is synoptic (I think), they would assume you remember stuff about alkanes and alkenes, as well as free radical substitution (the role of UV light in form radicals). But I don't think will play a big part in the paper.
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    DOES ANYONE HAVE A DOCUMENT CONTAINING MARK SCHEME ANSWERS TO COMMON/RE-OCCURING QUESTIONS? WOULD BE MUCH APPRECIATED.

    (ps - sorry for the caps)
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    http://qualifications.pearson.com/co...e_20120613.pdf

    Why is 15ei the 2nd H on the very bottom?

    Is it because it is attached to a C which is attached to a C with 2 Hs on it?
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    (Original post by baymax96)
    thats what i thought
    but on the jan 2010 paper, the answer for number 1 is B:/
    Oh, I think we are overcomplicating it.

    If the pressure increases, the side of the equation with fewer moles is favoured, so more PCl5 is produced, so it's mole fraction goes up. Kp is unaltered, only temperature directly changes it.
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    (Original post by Nautic4l)
    http://qualifications.pearson.com/co...e_20120613.pdf

    Why is 15ei the 2nd H on the very bottom?

    Is it because it is attached to a C which is attached to a C with 2 Hs on it?
    Spot on
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    Why does SN1 produce racemic and SN2 doesnt?


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    (Original post by baymax96)
    thats what i thought
    but on the jan 2010 paper, the answer for number 1 is B:/
    See my post earlier on the thread:

    http://www.thestudentroom.co.uk/show...=#post56808187
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    (Original post by Nautic4l)
    http://qualifications.pearson.com/co...e_20120613.pdf

    Why is 15ei the 2nd H on the very bottom?

    Is it because it is attached to a C which is attached to a C with 2 Hs on it?
    Yes
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    (Original post by AffirmedCube)
    We need to know it for unit 5, I'm sure. Just to be on the safe side, it would help to know the steps, but I doubt it would be asked. You just need to know that it is used to purify the product, to find out the carbonyl that had react with Brady's, me thinks.
    It came up on the 2015 Jan international paper so I'm learning the stages. It's only a few steps anyway
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    In Sn1 reactions, the intermediate carbocation is trigonal planar in shape, meaning that the OH- ion can attack the molecule from above or below the plane with equal likelihood. As a result, equimolar amounts of both enantiomers are formed.

    Sn2 reactions happen in one step, so no planar intermediate is formed. Instead the OH- ion can only attack the halogenoalkane on the side directly opposite the halogen - forming an optically active mixture with only one enantiomer.
    Lemme know if you want clarification.

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