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    Can someone please help me with q8b in the June 2012 paper.

    Thanks
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    can anybody explain why complex ions are coloured- as in visible light and stuff??

    and when do u multiply by 2 or by 0.5 when doing born haber cycles and lattice calculations?
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    I hate how science works questions fffffffs
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    has everyone done the jan 13 paper and how well did you do?
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    (Original post by Learner_108)
    Fe(h20)3(oh)3 , Cr(h20)3(oh)3 , Cu(h20)3(oh)3 ,
    Can anyone tell me the colours for these?


    Posted from TSR Mobile
    Brown solid, Green precipitate, respectively. Not sure about Cu(h2o)3(oh)3
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    Why does Al2O3 has a lower melting point than MgO, even though it is smaller and more highly charged?!
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    (Original post by ayshapatel)
    can anybody explain why complex ions are coloured- as in visible light and stuff??

    and when do u multiply by 2 or by 0.5 when doing born haber cycles and lattice calculations?
    Complex ions are coloured because light is absorbed by electrons in the d sub level, exciting them. They absorb some wavelengths of light but not all, the ones reflected are the ones you see.

    And for the 1/2, the example I can think of is the atomisation enthalpy is half of the bond dissociation of Cl2.
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    (Original post by ayshapatel)
    can anybody explain why complex ions are coloured- as in visible light and stuff??

    and when do u multiply by 2 or by 0.5 when doing born haber cycles and lattice calculations?
    -Complex ions absorbs light from spectrum
    -Electrons move to higher energy d orbital
    -Combination of colours not absorbed is reflected (the colour of the complex)

    You multiply the atomisation of Cl by 2 when its bonded to a group 2 metal.
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    (Original post by dizzy17)
    on the jan 2011 paper for 7c, how do they get the balanced equation between the hydrogen peroxide and manganate ions? is there a quick way of working it out or is it just trial and error?
    You're meant to know it.

    Oxidation- H2O2 -> O2 + 2H+ + 2e-
    Reducation- MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O

    Overall:
    2MnO4- + 6H+ + 5H2O2 -> 2Mn2+ + 8H20
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    (Original post by OFoster)
    Why does Al2O3 has a lower melting point than MgO, even though it is smaller and more highly charged?!
    It might be because MgO has ionic bonding whereas Al2O3 has ionic bonding but with covalent character so it weakens it.
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    (Original post by popnit)
    Please could someone explain the equation for reaction 2 in this paper. Qs 8a http://filestore.aqa.org.uk/subjects...5-QP-JUN12.PDF
    Reaction two occurs when its left in the prescence of oxygen, oxygen oxidises it to Co3+

    Or you can use hydrogen perioxide to oxidise Co2+
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    do we need to be able to draw EDTA?? STRESSING
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    (Original post by OFoster)
    Why does Al2O3 has a lower melting point than MgO, even though it is smaller and more highly charged?!
    Al203 has covalent character
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    (Original post by 16dan2life)
    You're meant to know it.

    Oxidation- H2O2 -> O2 + 2H+ + 2e-
    Reducation- MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O

    Overall:
    2MnO4- + 6H+ + 5H2O2 -> 2Mn2+ + 8H20
    Can you say H2O2 -> 2OH- + 2e- ??
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    (Original post by dobbie180)
    do we need to be able to draw EDTA?? STRESSING
    nope
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    (Original post by lala12)
    Can you say H2O2 -> 2OH- + 2e- ??
    yes
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    (Original post by lala12)
    Can you say H2O2 -> 2OH- + 2e- ??
    The overall equation won't come out right, as the reduction reaction has no OH- ions

    when H2O2 is oxidising it's
    H202 + 2e- -> 2OH-
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    (Original post by dobbie180)
    do we need to be able to draw EDTA?? STRESSING
    Nope!
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    How does Cr(H2O)6^3+ react with NH2CH2CH2NH2? In terms of the equation? Thanks


    Posted from TSR Mobile
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    (Original post by dobbie180)
    do we need to be able to draw EDTA?? STRESSING
    Doubt it. You need to know however that it acts as a multidentate by donating its lone pairs of electrons, which are present on 2 nitrogen and 4 oxygen atoms.
 
 
 
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