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    (Original post by RayMasterio)
    Okay, suppose it just asked for the emf of Copper. By this logic, if the equilibrium shifted left then the overall cell emf becomes positive? because it's losing electrons?


    Edit: Or is it because it moves to the left, the cu2+ is gaining more electrons and so the emf of the cell is negative?
    The eq shifted left, decreasing conc of Cu2+ AND decreasing the electrode potential (also, the E is not standard as conc is no longer standard, below 1moldm-3)

    Hope that made sense
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    guys can anyone help me with June 2015 question 2d part i, q 4c part ii, and part d iii
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    (Original post by zirak46)
    The eq shifted left, decreasing conc of Cu2+ AND decreasing the electrode potential (also, the E is not standard as conc is no longer standard, below 1moldm-3)

    Hope that made sense
    I cant rep you but it makes sense. Thanks mate.
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    Can someone explain rate determining steps to me?
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    (Original post by Dinasaurus)
    Can someone explain rate determining steps to me?
    Check out "machemguy" on YouTube. He explains it pretty well.
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    (Original post by RayMasterio)
    I cant rep you but it makes sense. Thanks mate.
    No worries, lets go 619 that exam
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    (Original post by zirak46)
    No worries, lets go 619 that exam
    Lol

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    When making up this years grade boundaries for f324, does OCR have to take last years grade boundaries into consideration? Can take they jump straight 8 marks and go from 42 from last year to 50 this year for an A?

    Just a little curious since thats not happened in the past, the biggest difference between 2 years has been 5 marks...
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    (Original post by four4)
    When making up this years grade boundaries for f324, does OCR have to take last years grade boundaries into consideration? Can take they jump straight 8 marks and go from 42 from last year to 50 this year for an A?

    Just a little curious since thats not happened in the past, the biggest difference between 2 years has been 5 marks...
    No, because the whole point of an exam is to be a distinctly-unique entity from the one preceding it. The only influence last year has is in how OCR choose to write their paper, etc.

    Everyone's grade is marked raw, so out of 60 for F324. If we plot everyone's results, we get a bell curve, where some people do horribly, some people do amazingly, and most do decently.

    Imagine we have 100000 students who sat F324. We take the top 10000 scores (top 10%) and we find out what the lowest member of this group got. Say they got 56. That means 56 is the A* boundary. Obviously candidate 10001 may also have 56, so they'll also get an A*. Then we look at the next 10000. Let's say the lowest member gets 50 - an A become an 50. Candidates 20001-20054 may all also have 50, so they'll all get A's. We repeat this until we account for all grade boundaries and all students.

    ^ This is how grade boundaries are decided. No outside influences, just cold hard data. That way, we have a consistent rubric to match marks against (by taking 10% samples) and usually little variation in the percentage of people attaining a certain grade; 8.39% of students last year got an A* compared to 7.67% in 2014. Everybody is happy c:


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    I've been hardcore prepping for this paper and I woke up at 6, just to realise it's tomorrow and today is maths. FML
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    (Original post by Dinasaurus)
    I've been hardcore prepping for this paper and I woke up at 6, just to realise it's tomorrow and today is maths. FML
    looooooooooooool.
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    (Original post by RayMasterio)
    guys can anyone help me with June 2015 question 2d part i, q 4c part ii, and part d iii
    2 d (i) N2O +H2 -> N2 + H2O
    If you look at step 2 N2O is produced but this isn't in the overall equation so must react again in step 3 to be converted into something that is. In the overall equation there is one mole of N2 and 2 moles of H2O and yet before step 3 you have no moles of N2 and one mole of H2O. Therefore N2O must be combined with something to form N2 and H2O. Hydrogen.
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    (Original post by rishani)
    Any predictions for tomorrow
    Chemistry.


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    (Original post by GetOverHere)
    Imagine we have 100000 students who sat F324. We take the top 10000 scores (top 10%) and we find out what the lowest member of this group got. Say they got 56. That means 56 is the A* boundary. Obviously candidate 10001 may also have 56, so they'll also get an A*. Then we look at the next 10000. Let's say the lowest member gets 50 - an A become an 50. Candidates 20001-20054 may all also have 50, so they'll all get A's. We repeat this until we account for all grade boundaries and all students.

    ^ This is how grade boundaries are decided. No outside influences, just cold hard data. That way, we have a consistent rubric to match marks against (by taking 10% samples) and usually little variation in the percentage of people attaining a certain grade; 8.39% of students last year got an A* compared to 7.67% in 2014. Everybody is happy c:


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    This is not correct at all.

    The only boundaries which are set by examiners are the Grade A and Grade E boundaries. These are decided by a mix of statistics (similar to what you mentioned), but also a review of candidate scripts from the current year and previous years, to ensure that the standard of work required to achieve each grade stays the same each year.

    Once the Grade A and Grade E boundaries are set then the rest of the boundaries are automatically generated such that there is an equal number of marks between each boundary. That is why the difference between A and A* is always equal to the difference between A and B.
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    (Original post by rishani)
    Any predictions for tomorrow
    hardest paper in the world
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    Would anyone mind helping me with question 3 (c) (ii) on the June 2012 paper? I seem to be getting the wrong number of moles for butanoic acid and I don't understand how or why the concentrations are calculated
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    Please someone explain the questions on ratios with buffers I don't get what the rationing actually means what does HCO3- : H2COH being 6.6:1 actually means?
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    Yeah the mark scheme for that paper seems wrong idk why I couldn't get the moles either :/

    (Original post by Lucy985)
    Would anyone mind helping me with question 3 (c) (ii) on the June 2012 paper? I seem to be getting the wrong number of moles for butanoic acid and I don't understand how or why the concentrations are calculated
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    Could some explain why the cell potential increases when water is added?
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    Just figured it out - they seem to jump a step in the mark scheme -_-
    They went straight to finding the excesss moles and didn't include the original moles at first

    (Original post by tcameron)
    Yeah the mark scheme for that paper seems wrong idk why I couldn't get the moles either :/
    (Original post by Lucy985)
    Would anyone mind helping me with question 3 (c) (ii) on the June 2012 paper? I seem to be getting the wrong number of moles for butanoic acid and I don't understand how or why the concentrations are calculated
 
 
 
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