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    Hello.

    Can anyone please explain the answer for 3b (half equation) from this specimen paper?
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    Thanks,

    Mark
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    (Original post by lifeisgood2012)
    Guys how would you do question 4biv and 4c??? and 5bii and 5cii???
    i have no ideaaa
    are these answers to the chem exam tomorrow ?
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    Hi!
    I'm really confused! Question 1c(iii) Jan 2013
    why did we have to use the BB-BF to find the enthalpy of formation?
    I though enthalpy of formation has it own sets of values??
    thanks!
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    is ther eany answers to the chem regents tomorrow?
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    I understand - thanks again


    (Original post by crc290)
    Well when you're writing cell representations, the most positive electrode goes on the right. The reduced species go furthest away from the salt bridge and the oxidised species go closest to the salt bridge. You're told you have to use platinum contacts. Since all of the species are aqueous, you can use commas to separate them instead of lines

    Pt | SO32-(aq), SO42-(aq) || ClO3-(aq), Cl-(aq) | Pt

    When you're writing overall equations, you always reverse the half-equation with the lower E value i.e.
    ClO3- + 6H+ + 6e- \rightarrow Cl- + 3H2O
    SO32- + H2O \rightarrow SO42- + 2H+ + 2e-

    Then just combine them as you usually would:
    ClO3- + 3SO32- \rightarrow Cl- + + 3SO42-

    ClO3- is reduced, so it must be the oxidising agent. SO32- is oxidised, so it must be the reducing agent

    Hopefully I've done everything right. If you need anything explained just quote me
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    Ratios for the titration questions:

    P4O10 4 H3PO4 (1:4)
    H3PO4 3 NaOH (1:3)
    Cr2O7 6 Fe (1:6)
    2MnO4 5 H2O2 (2:5)
    2MnO4 5 C2O4 (2:5)
    H2O2 and Chromium (3:2)
    H2O2 and Cobalt (1:2)

    Anyone see any mistakes, or have any more to add kindly do so!
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    Just done another past paper. 90/100 :woo:

    Need to go over the explanation for the colours 'cause I keep losing a mark on that. Need to work on the explanation on why a reaction will not be feasible when you increase/decrease temp. I understand the whole thing but I'm not hitting the marks :rolleyes:
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    (Original post by AmyLH)
    Just done another past paper. 90/100 :woo:

    Need to go over the explanation for the colours 'cause I keep losing a mark on that. Need to work on the explanation on why a reaction will not be feasible when you increase/decrease temp. I understand the whole thing but I'm not hitting the marks :rolleyes:
    Just woke up because I was thinking of the colours I thought I had remembered lol

    I have a similar problem

    Colours = Light energy is absorbed, this excites electrons in the 3d sub-shell, the colour reflected is a mixture of the colours left behind

    Entropy will depend upon whether the enthalpy change of the reaction is positive or negative as well as the entropy

    e.g a negative enthalpy + positive entropy, increased temp will make gibbs free-energy change negative so reaction feasible
    positive enthalphy +negative entropy, increased temp will make gibbs free energy positive because a the negative sign in entropy becomes a positive

    Hope that makes sense, is a little late/early lol
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    Is the electronegativity of an atom different from the electronegativity between atoms?
    On the period 3 elements, the electronegativity of individual atoms increase as go across - but the electronegativity between atoms in the oxides decrease as go across- is this right?

    Also what is the difference between electronegativity and polarising power? they seem similar
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    Does anyone know where I can find paper and mark scheme for Jan 2013!?! Need it pretty bad. Thanks
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    When writing cell representations, when you write what the electrodes are made of? Also, when is it just platinum?
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    (Original post by 16dan2life)
    that was part of the legacy spec, synoptic stuff was required. Not for us
    Are you sure?I thought this module was synoptic too?
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    (Original post by antonio108)
    When writing cell representations, when you write what the electrodes are made of? Also, when is it just platinum?
    I think a platinum electrode is used when the reactant/product is non solid. So if it's aqueous or gaseous a platinum electrode is used to conduct electrons.

    e.g Pt|H2(g)|2H+(aq) ||
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    may be a stupid.question but can someone tell me how can u tell a.cell.is rechargeable
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    In the june 12 paper how are you supposed to know the reaction between phosphoric acid and magnesium oxide? Qs 1e(i) if anyone wants to take a look

    Posted from TSR Mobile
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    Please help me with this question, its so hard
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    (Original post by TaraBelle)
    Are you sure?I thought this module was synoptic too?
    I had a look at the specification about whether this unit was synoptic, and it said that all A2 units do have to have some synoptic element, and although this isn't an entirely separate assessment, it is sort of woven into the questions e.g. stuff like bond angles and oxidation states which are in the first unit.
    However this unit doesn't have synoptic stuff from unit 4 (and probably most of unit 2 as these units both featured lots of organic chemistry) as unit 4 and 5 can be taken in any order
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    (Original post by popnit)
    In the june 12 paper how are you supposed to know the reaction between phosphoric acid and magnesium oxide? Qs 1e(i) if anyone wants to take a look

    Posted from TSR Mobile
    You're supposed to know how each p3 reacts as an acid or base
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    (Original post by Beth_L_G)
    You're supposed to know how each p3 reacts as an acid or base
    Yeah but this is a reaction with an oxide which is neither an acid nor a base

    Posted from TSR Mobile
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    (Original post by popnit)
    Yeah but this is a reaction with an oxide which is neither an acid nor a base

    Posted from TSR Mobile
    The oxide is a base in terms of Bronsted-Lowry as it accepts protons (H+) from the phosphoric acid
 
 
 
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