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Equilibria, Energetics and Elements (F325) - June 2011 Exam. watch

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    (Original post by apo1324)
    Could someone please tell me where 34 has come from in the answer to 7b of the June 2010 paper. http://www.ocr.org.uk/download/pp_10...n_gce_f325.pdf

    Thanks.
    Isn't that just the Mr of H2O2?
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    (Original post by apo1324)
    Could someone please tell me where 34 has come from in the answer to 7b of the June 2010 paper. http://www.ocr.org.uk/download/pp_10...n_gce_f325.pdf

    Thanks.
    You mean in the mark scheme?

    34 is the Molar mass of H202
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    (Original post by student777)
    Isn't that just the Mr of H2O2?
    Oh i see, where has 40 come from? I can't count. :L The mark scheme multiplies the moles by 40 and 34.

    Sorry for the stupid questions.
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    (Original post by apo1324)
    Oh i see, where has 40 come from? I can't count. :L The mark scheme multiplies the moles by 40 and 34.

    Sorry for the stupid questions.
    I don't understand where the 40 has come from:confused:
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    (Original post by Jtking3000)
    http://www.qfpost.com/download.do?ge...13b8f2f3ff8d26

    i've uploaded the examination style question answers if thats what you need
    Thank you sooo much!! that is exactly what i needed!
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    (Original post by apo1324)
    Oh i see, where has 40 come from? I can't count. :L The mark scheme multiplies the moles by 40 and 34.

    Sorry for the stupid questions.
    (Original post by CoventryCity)
    I don't understand where the 40 has come from:confused:
    1/0.025, 0.025 being the volume of H2O2
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    (Original post by Jtking3000)
    1/0.025, 0.025 being the volume of H2O2
    Ahh agreed I forgot you need to divide by volume/1000
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    For the last part of 7b) about the O2 volume how have they done it?
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    (Original post by CoventryCity)
    For the last part of 7b) about the O2 volume how have they done it?
    for every 2 moles of MnO4- reacting with 5 moles of H2O2 it creates 5 moles of O2 which makes is 1.1725x10^-3 moles in this case since there is 4.69x10^-4 moles of MnO4-

    1 mole of O2 occupies 24dm^3 so 1.1725x10^-3 moles of O2 occupies 24x1.1725x10^-3= 0.0281dm^3

    basically a recap of atoms bonds and groups.
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    Just redid the jan 2011 and got 80/100 as i thought it would be good practice to do it again .

    First time i did it was in the easter hols when we were yet to finish all the topics and had some thing along the lines of 55/100. There are some questions on here i have absolutely no idea how to answer and staring at the mark sheme until it makes sense isnt helping either :sad:.
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    Could someone please explain to me how to do 6d on jan11 peper. I understand what points we have to mention but I don't understand why the enthalpy change of solution of KF is less negative than of RBF. If K+ ion has a smaller radius, whould it not have more negative enthalpy change of solution as its lattice enthalpy would be more negative...


    I would also appreciate some help on the first question of specimen paper on determining rates. This may seem easy and sorry for asking stupid questions.

    Thank you
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    (Original post by Mie Peson)
    Could someone please explain to me how to do 6d on jan11 peper. I understand what points we have to mention but I don't understand why the enthalpy change of solution of KF is less negative than of RBF. If K+ ion has a smaller radius, whould it not have more negative enthalpy change of solution as its lattice enthalpy would be more negative...


    I would also appreciate some help on the first question of specimen paper on determining rates. This may seem easy and sorry for asking stupid questions.

    Thank you
    I was confused about this as well but from what I understand it is because a smaller ionic radius will also give a larger exothermic value for the lattice enthalpy. For the enthalpy of solution the lattice has to be broken down so in the Q you have to say the smaller ionic radius has a more significant effect on the lattice enthalpy than the enthalpy of hydration meaning KF will be less exothemic

    I'm not sure if I explained that very well or even correctly, we did this Q in lesson today and it was very confusing

    Breaking down the lattice is the opposite of lattice enthalpy so is a +ve value with the same magnitude, so the larger the lattice enthalpy means it becomes less exothemic
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    I hope theres hairdessing pt II included.
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    (Original post by waecskt)
    I hope theres hairdessing pt II included.
    My favourite question on Jan 2011
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    (Original post by waecskt)
    I hope theres hairdessing pt II included.
    This actually made me laugh out loud. Quite an achievement for a chemistry thread
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    That was the worst question ever lol nobody I know has got that right.

    Probably because I can't perm my hair
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    Can someone please exaplain to me how you write redox reactions, and half equations?
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    (Original post by CoventryCity)
    I was confused about this as well but from what I understand it is because a smaller ionic radius will also give a larger exothermic value for the lattice enthalpy. For the enthalpy of solution the lattice has to be broken down so in the Q you have to say the smaller ionic radius has a more significant effect on the lattice enthalpy than the enthalpy of hydration meaning KF will be less exothemic

    I'm not sure if I explained that very well or even correctly, we did this Q in lesson today and it was very confusing

    Breaking down the lattice is the opposite of lattice enthalpy so is a +ve value with the same magnitude, so the larger the lattice enthalpy means it becomes less exothemic
    Yeah that makes sense. I did not think of breaking down of lattice enthalpy being positive. By the way could you please on 2d on specimen paper. I keep on getting 0.013moldm-3 but the answer is 0.13moldm-3.

    Thanks again
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    If you've ever gotten an A in a chemistry module, be it in AS or A2, how did you revise? Did you tackle every past paper in sight? Have extra lessons outside school (tutorials), Read all the way into the night?

    Im really curious to know people's revision strategy. I feel the need to change mine... (please quote me when you reply)
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    (Original post by mauvetard)
    If you've ever gotten an A in a chemistry module, be it in AS or A2, how did you revise? Did you tackle every past paper in sight? Have extra lessons outside school (tutorials), Read all the way into the night?

    Im really curious to know people's revision strategy. I feel the need to change mine... (please quote me when you reply)
    For Atoms, Bonds and Groups, first time round I got a C, retook and got a high A. I basically briefly learnt all the content then did past papers until I literally got sick at the sight of them! You do a few when you start so you know your weak areas. Then go over contennt you keep getting wrong. Then practice exam technique. Practise papers are manna from heaven for me! :P

    Though it helped that it was a retake so I already knew most of it, and it's so easy compared to other A2 stuff.

    Hope this helps

    Don't ask what i'm doing up at this hour... xD
 
 
 
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