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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 Internets)
    With electronegativity questions, would it be better I wrote about the specific dipole-dipole interactions or just say van der Waals' or London forces?

    Also, just to clarify, are van der Waals' referring to induced and permanent and London only induced?
    I wouldn't say van der Waals. I don't think they want that anymore. Instead refer to either london forces, permanent dipoles and hydrogen bonding
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    (Original post by Internets)
    With electronegativity questions, would it be better I wrote about the specific dipole-dipole interactions or just say van der Waals' or London forces?

    Also, just to clarify, are van der Waals' referring to induced and permanent and London only induced?
    Generally the mark scheme will say allow van der Waals when talking about London forces. I think it's because on the old spec they mentioned that van der Waals is induced dipole dipole interaction (London forces) and this year they changed the name but some people are retaking so the van der Waals is still acceptable
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    (Original post by 4nonymous)
    I wouldn't say van der Waals. I don't think they want that anymore. Instead refer to either london forces, permanent dipoles and hydrogen bonding
    The mark scheme will, most likely, say allow van der Waals when talking about London forces
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    (Original post by ashbawa)
    The way we have been taught is that to state the interactions between the molecules depending on the difference in electronegativity, I don't use van der waals. I either use london forces (induced), permanent dipole-dipole interactions or hydrogen bonding
    (Original post by 4nonymous)
    I wouldn't say van der Waals. I don't think they want that anymore. Instead refer to either london forces, permanent dipoles and hydrogen bonding
    (Original post by asinghj)
    Generally the mark scheme will say allow van der Waals when talking about London forces. I think it's because on the old spec they mentioned that van der Waals is induced dipole dipole interaction (London forces) and this year they changed the name but some people are retaking so the van der Waals is still acceptable


    Thanks for the help guys!

    For past papers, is the content for our exam only in f321 and f322? These are the only papers we have done in my class. Are there topics missing from those papers I need to be aware of?
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    (Original post by Major Wilson)
    Good luck for tomorrow everyone
    Wait wtf... Isn't it on Friday!?
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    Omg I had heart palpitations mannn..

    Checked my timetable.. It is on Friday. Pleasant surprise to find out it was an evening exam. I though it was in the am but that was the last paper. Ahh yes so happy!!
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    (Original post by Major Wilson)
    Good luck for tomorrow everyone
    Thanks mate
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    Does anyone have a prediction on what the extended answer questions could be?
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    (Original post by asinghj)
    The mark scheme will, most likely, say allow van der Waals when talking about London forces
    Yh I think it does, but I would just prefer to say london forces because its the preferred answer
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    (Original post by Internets)
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    Thanks for the help guys!

    For past papers, is the content for our exam only in f321 and f322? These are the only papers we have done in my class. Are there topics missing from those papers I need to be aware of?
    Ideal gas equation
    Maybe of few others but i'm not sure
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    Does anyone have the mark scheme to the other depth paper that isn't on the ocr website??
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    http://www.ocr.org.uk/Images/65360-q...-resources.pdf

    q 3b ii why do you times by two? is it because of the 2:1 ratio?


    MS has:

    (2 x 2.3) / 0.2 = 23 kJ mol-1

    The MS would accept 12 kJ mol-1 but not sure if it will this year
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    (Original post by Jitesh)
    ...
    The standard enthalpy change of a reaction is the enthalpy change which occurs when equation quantities of materials react under standard conditions, and with everything in its standard state.
    I guess it is because of the ratio.
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    (Original post by Vanilla Poison)
    I guess it is because of the ratio.
    I don't fully understand why we times it by two when the moles that reacted was 0.200 ?
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    (Original post by Jitesh)
    I don't fully understand why we times it by two when the moles that reacted was 0.200 ?
    I don't really get why myself, perhaps this will help.
    Examiners report:
    The mark scheme allowed +12 kJ mol–1 as an alternative answer which is not the enthalpy change of reaction but is the enthalpy change per mole of NH4SCN.
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    (Original post by Vanilla Poison)
    I don't really get why myself, perhaps this will help.
    Examiners report:
    Yeah I also read that as well and still don't fully understand, I'm just worried they wouldn't accept enthalpy change per mole of NH4SCN this year.. hmmm

    Thanks though!!
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    (Original post by Jitesh)
    Yeah I also read that as well and still don't fully understand, I'm just worried they wouldn't accept enthalpy change per mole of NH4SCN this year.. hmmm

    Thanks though!!
    No worries man, I think I kinda get it now. This Wikipedia article is quite good.
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    https://youtu.be/LUE6tj1-_z4
    Last minute mechanisms revision video
    good luck everyone!
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    (Original post by Vanilla Poison)
    No worries man, I think I kinda get it now. This Wikipedia article is quite good.
    Ah, I see now - so it is to do with the molar quantities

    Why does it show adding the sum of the stoichiometric number of entity B?

    Edit: nevermind misread it

    Thanks a bunch! Not seen a question like that before lol
 
 
 
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