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    I don't suppose anyone has a list of colours for [M (Cl)4]2-/- complex ions do they? They seem to come up periodically (heh) in the past papers, but I can't find a list in the textbook. Which is strange, as it's not at all like AQA to write a bad textbook, or to ask you questions that haven't come up in said book.

    Tangent, here, but one thing that particularly annoys me is their definition of enthalpy of hydration.
    In the mark scheme of a paper where it asks you to define it, it specifically says to ignore that definition.
    Figures.
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    (Original post by Grauniad)
    I don't suppose anyone has a list of colours for [M (Cl)4]2-/- complex ions do they? They seem to come up periodically (heh) in the past papers, but I can't find a list in the textbook. Which is strange, as it's not at all like AQA to write a bad textbook, or to ask you questions that haven't come up in said book.

    Tangent, here, but one thing that particularly annoys me is their definition of enthalpy of hydration.
    In the mark scheme of a paper where it asks you to define it, it specifically says to ignore that definition.
    Figures.
    ohh yeah, the definition in the textbook says something about water molecules, and the markscheme says do not allow any mention of water molecules..FFS. made me distrustful of all the other standard definitions :/

    as for the chlorine complexes, ive learnt [CoCl4]2- as blue solution
    [CuCl4]2- as yellow green solution. and they match up to mark scheme answers.
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    (Original post by gooner1886)
    Could you please talk me through 5(b) on the Jan 11 paper (http://filestore.aqa.org.uk/subjects...W-QP-JAN11.PDF)
    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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    (Original post by Puffy14)
    Thank you, why are ionic oxides alkaline? Because the O2- attracts H on water to form hydroxides?
    Yeah I think so
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    (Original post by Grauniad)
    I don't suppose anyone has a list of colours for [M (Cl)4]2-/- complex ions do they? They seem to come up periodically (heh) in the past papers, but I can't find a list in the textbook. Which is strange, as it's not at all like AQA to write a bad textbook, or to ask you questions that haven't come up in said book.

    Tangent, here, but one thing that particularly annoys me is their definition of enthalpy of hydration.
    In the mark scheme of a paper where it asks you to define it, it specifically says to ignore that definition.
    Figures.
    [CoCl4]2- is blue
    [CuCl4]2- is yellow

    Those are the only two we need to know
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    (Original post by candyhearts)
    Please could someone type which equations we need to know for hydrogen peroxide, also what would be the equations of cobalt oxidation in amoniacal solution? Would it just be the normal ligand substitution reaction?
    Reduction:
    H2O2 + 2H+ + 2e- \rightarrow 2H2O or H2O2 + 2e- \rightarrow 2OH-
    Oxidation:
    H2O2 \rightarrow O2 + 2H+ + 2e-

    Cobalt (II) in ammoniacal solution is [Co(NH3)6]2+. It can be oxidised to [Co(NH3)6]3+, but there is no ligand substitution

    Hope this helps
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    do you guys draw arrows for complex ions? I haven't seen it in the mark scheme but :/
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    (Original post by MrMeep2580)
    you're meant to learn a certain equation

    It is:

    5e- + MnO4^(-) + 8H^(+) --> Mn^(2+) + 4H2O

    then know that they want

    Fe --> Fe^(+) + e-

    So the ratio is 1:5, same with the Cr2O7^(2-) equation to learn, that ratio is 1:6
    In the case of this question it said the reduction of Fe2+ ions, so how are we meant to know if it is reduced to Fe+ or to Fe?

    Edit: ooopss okay I see, MnO4 - is being reduced so Fe2+ ions must be being oxidised to Fe3+ which is a ratio of 1:5 sorry
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    (Original post by itssochaotic)
    do you guys draw arrows for complex ions? I haven't seen it in the mark scheme but :/

    I normally do,

    It shows Dative covalent bonding
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    (Original post by itssochaotic)
    do you guys draw arrows for complex ions? I haven't seen it in the mark scheme but :/
    yes cause an arrow represents a coordinate bond
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    Does anyone have a list of all the possible colours for Chromium compounds and ions?
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    (Original post by BossmanYabz)
    Does anyone have a list of all the possible colours for Chromium compounds and ions?
    [Cr(H2O)6]3+ : Ruby
    [Cr(H2O)6]2+ : Blue
    CrO4 2- : Yellow
    Cr2O7 2- : Orange
    [Cr(H2O)3(OH)3](s) : Green
    [Cr(OH)6]3- : Green
    [Cr(NH3)6]3+ : Purple

    Those are all the ones we need I think


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    2 Exams left! This and Physics unit 5, I can almost taste the freedom!


    Time to get revising...
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    (Original post by BossmanYabz)
    Does anyone have a list of all the possible colours for Chromium compounds and ions?
    Cr2O72- = Orange
    CrO42- = Yellow
    Cr3+ = Green
    Cr2+ = Blue

    [Cr(H2O)6]3+ = Ruby sol.
    With OH-/NH3 = Green ppt.
    With excess OH- = Green sol. --> [Cr(OH)6]3-
    With excess NH3 = Purple sol.
    With Sodium Carbonate = Green ppt.

    So variants between orange, yellow, green, blue, ruby & purple :L
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    I would love it if someone posts all the equations we need to know
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    does anyone have the january 2013 question paper and mark scheme please?!!
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    (Original post by flyylikejetz)
    Cr2O72- = Orange
    CrO42- = Yellow
    Cr3+ = Green
    Cr2+ = Blue

    [Cr(H2O)6]3+ = Ruby sol.
    With OH-/NH3 = Green ppt.
    With excess OH- = Green sol. --> [Cr(OH)6]3-
    With excess NH3 = Purple sol.
    With Sodium Carbonate = Green ppt.

    So variants between orange, yellow, green, blue, ruby & purple :L

    This what was getting me a little confused, do the variants apply just to the Cr3+ ion? I'm sure there is a question that asks about it but I can't seem to find it. Do you know what paper it is?
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    How do you know whether to draw the structure in 3D or just to show coordinate bonds? As a question which says:

    'Draw a diagram to show the shape of and bonding in the complex product' surely shape implies they wanted it wedge and dotted bonds, but they just wanted 6 bonds with arrows shown
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    ok I can never gauge if my answers to the wordy/explainy type questions match with the mark scheme. eg for Q 7a June 2011 I've written

    "the d electrons become excited and move up to a higher energy level on absorbing visible light. the colour observed corresponds to the part of the visible light spectrum that has been transmitted."

    Mark scheme says:
    absorbs (certain frequencies of) (white) light / photons
    d electrons excited / promoted
    the colour observed s the light not absorbed / light reflected / light transmitted

    Is my answer ok?? :/
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    (Original post by BossmanYabz)
    This what was getting me a little confused, do the variants apply just to the Cr3+ ion? I'm sure there is a question that asks about it but I can't seem to find it. Do you know what paper it is?
    Not to sure what paper but yeah there are separate chromium reactions that we need to know. Brief summary:

    Cr2O72- when you add (OH-) will form CrO42- and if you add H+ the reaction will go the other way because they exist in an equilibrium.

    They can also be oxidised and reduced so:
    Cr2O72- with Zn/Dilute acid can be reduced to Cr3+ and Cr3+ can be oxidised with Hydrogen peroxide/OH- to form CrO42-.

    Cr3+ can also be further reduced by Zn/H+ again to form Cr2+ however this is rare because of the instability of the Cr2+ thus only occurs in an inert atmosphere, but naturally the Cr2+ will be oxidised by air back to Cr3+.

    So mainly you need to know for reduction Zinc/H+.... for oxidation H2O2/OH-

    and the equilibrium:
    Cr2O72- + H2O --> 2CrO42- + 2H+
 
 
 
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