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    (Original post by frogs r everywhere)
    Its not a hard chapter. What do you need to know?

    If an entity has a higher E standard value, it gets reduced.
    If another entity has a lower e standard value, it gets oxidised.

    This now apples to all questions to do with emf.
    ok so whats a salt bridge? Thanks btw
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    can someone please explain to me what the function of the electrolyte is in electrochemics cells? why is it in some cells and not others? and why is it needed in the hydrogen oxygen fuel cells ??
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    (Original post by ChemBoss)
    ok so whats a salt bridge? Thanks btw
    a salt bridge allows ions to flow through and balances out the charges
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    do we need to know the flames colours for the p3 oxides?
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    (Original post by coolstorybrother)
    do we need to know the flames colours for the p3 oxides?
    yes
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    (Original post by coolstorybrother)
    do we need to know the flames colours for the p3 oxides?
    go back a couple pages. They're written there :-D
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    (Original post by louise_234)
    can someone please explain to me what the function of the electrolyte is in electrochemics cells? why is it in some cells and not others? and why is it needed in the hydrogen oxygen fuel cells ??
    Anelectrolyte is basically a fluid with ions dissolved into it. Sometimes a polymer fluid is used because this can conduct a current whilst remaining viscous to prevent leaking out. (This is why an electrolyte is used in mobile phone batteries) the hydrogen oxygen fuel cell needs an electrolyte because (I think) water may react if the reaction uses aqueous reactant. So the electrolyte is there to be inert and good at electrical conduction.
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    I've been so inconsistent in past papers.
    ive done 3 and got 72,76,81

    its so annoying, some papers seem to be harder than others,

    though on all these I lost round 10 marks on colours since I haven't bothered to revise them yet :P
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    Oh dear haven't started Past papers for this yet...
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    I am terrible at redox equilibria ! When writing the cell diagram how do you figure out which way around each half cell is ?
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    Have you guys learnt most of the content?


    Posted from TSR Mobile
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    (Original post by lmon)
    I am terrible at redox equilibria ! When writing the cell diagram how do you figure out which way around each half cell is ?
    The more positive value is always on the right hand side, except for the standard hydrogen electrode which must always be on the left
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    Has anyone got a list of all the definitions you need to know for this exam?
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    when doing the conventional representation of electrochemical cells, are there phase boundaries between aqueous and liquid? because on january 2010 paper question 3c it doesn't show phase boundaries between them, unless it is because the commas are seperating reactants and products?
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    (Original post by RoaringLion)
    Have you guys learnt most of the content? Posted from TSR Mobile
    There's not much content really
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    (Original post by louise_234)
    when doing the conventional representation of electrochemical cells, are there phase boundaries between aqueous and liquid? because on january 2010 paper question 3c it doesn't show phase boundaries between them, unless it is because the commas are seperating reactants and products?
    No phase boundary as an aqueous solution is in liquid phase. At our level only 3 phases exist.

    Posted from TSR Mobile
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    (Original post by Chewy29)
    No phase boundary as an aqueous solution is in liquid phase. At our level only 3 phases exist.

    Posted from TSR Mobile
    thank you
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    (Original post by Dirtybit)
    Oh dear haven't started Past papers for this yet...
    Same I'm doing chem 2, 4 and 5 but I'm worried I'm leaving chem 5 too late
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    Please can someone explain the answer to question 3(c) on the CHM5 Jan 2005 Paper. It's on electrochemical cells and I have no idea how they get the answer in the mark scheme.

    Thanks.
    Attached Images
  1. File Type: pdf AQA-CHM5-W-QP-JAN05.pdf (119.5 KB, 110 views)
  2. File Type: pdf AQA-CHM5-W-MS-JAN05.pdf (158.2 KB, 265 views)
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    (Original post by brittanna)
    Please can someone explain the answer to question 3(c) on the CHM5 Jan 2005 Paper. It's on electrochemical cells and I have no idea how they get the answer in the mark scheme.

    Thanks.
    The emf of the reaction "VO2+(aq) + 2H+(aq) + e– → VO2+(aq) + H2O(l)" is less than the one for MnO4- so V2+ makes V3+ which makes VO(2+) which makes VO2(+). The MnO4- must be reduced.

    VO2+ +5 + -4 = +1

    And the equation should be pretty straight forward once you know the final species because you just balance the oxygen and water etc.

    Hope that helped because that first part is always hard to explain!
 
 
 
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