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    (Original post by shiney101)
    I think you're getting confused with delta G, a reaction would happen (feasible) if delta G is negative, but with entropy the more disordered the more positive it becomes.
    Ooohh thanks!
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    (Original post by RedDevil1997)
    Does anyone have the Chem 5 2015 mark scheme pleaseee
    Thanks in advance
    Its online on the AQA website
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    What are all the types of reactions?

    There's ligand substitution
    There's acid base

    Anymore?






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    (Original post by Super199)
    Someone help with 3c and 4a pls

    http://filestore.aqa.org.uk/subjects...W-QP-JAN10.PDF
    4a the bond enthalpy is twice the atomisation enthalpy

    3c im stuck on it too
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    (Original post by joebush)
    How much does everyone know about spectophotometry/colorimetry? I know it's not on the spec but it links into the aqua ions and titrations sections.
    colorimetry is on the spec .... 3.5.4 under formation of coloured ions : we need to know how to determine concentration from from relative absorption of light, using a calibration graph
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    (Original post by Anam)
    4a the bond enthalpy is twice the atomisation enthalpy

    3c im stuck on it too
    Do you mind explaining why it is twice atomisation enthalpy?
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    Does anyone know the full equation for fe(h2o)4(oh)2 with oxygen to form fe(h20)3(oh)3?
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    (Original post by 1/2(p^2-p))
    colorimetry is on the spec .... 3.5.4 under formation of coloured ions : we need to know how to determine concentration from from relative absorption of light, using a calibration graph
    Ah, thanks a lot. Luckily I had revised it, I was just hoping it wasn't in vain.
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    Can someone explain the colorimetry thing with the calibration curve?
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    (Original post by Super199)
    Can someone explain the colorimetry thing with the calibration curve?
    you plot a graph using known concentrations and known absorption's then use this graph to find the concentration of an unknown ion by reading of the calibration graph... so say you want to kno the conc of ion X you plot graph using known conc's of X and its relative absorbance then use this graph to find an the conc of a unknown sample of X when you kno its absorption
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    (Original post by shiney101)
    I think you're getting confused with delta G, a reaction would happen (feasible) if delta G is negative, but with entropy the more disordered the more positive it becomes.
    what about enthalpy of solution? Is it more feasible if it is negative or positive?
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    (Original post by thehollowcrown)
    Can someone help me with bidentate ligands and M3+ ions? I assumed they would react in the same way as M2+ ions but according to http://filestore.aqa.org.uk/subjects...5-QP-JAN12.PDF Q8ei they don't. Why is this?
    I was confused when I did this paper too. You have to realise that en is going to act as a base. Aluminium doesn't undergo ligand exchange with ammonia:

    [Al(H2O)6]3+ + 3NH3 --------> [Al(H2O)3(OH)3] + 3NH4+

    So the same thing happens with en:

    2[Al(H2O)6]3+ + 3(NH2CH2CH2NH2)--------> 3[Al(H2O)3(OH)3] + 3(NH2CH2CH2NH2)
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    (Original post by youngar)
    I was confused when I did this paper too. You have to realise that en is going to act as a base. Aluminium doesn't undergo ligand exchange with ammonia:

    [Al(H2O)6]3+ + 3NH3 --------> [Al(H2O)3(OH)3] + 3NH4+

    So the same thing happens with en:

    2[Al(H2O)6]3+ + 3(NH2CH2CH2NH2)--------> 3[Al(H2O)3(OH)3] + 3(NH2CH2CH2NH2)
    Ohh, that makes so much more sense now, thank you!
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    (Original post by Super199)
    Do you mind explaining why it is twice atomisation enthalpy?
    Ok, so what I did was to look at the compound being formed, silver chloride. We all know that silver chloride has only one Cl- ion, and so during the atomisation of Cl2, the born haber cycle (an imaginative one) would already have 1/2 Cl2 to make one Cl, therefore the enthalpy shown in the table is only of one cl atom. So if Cl-Cl is broken, twice the amount of energy would be needed. I hope this helps.
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    Can someone explain why with some of the complex with excess NH3 you get full substitution and some you don't

    Like cobalt gives [Co(NH3)6]2+ but copper doesn't for example
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    (Original post by shiney101)
    Does anyone know the full equation for fe(h2o)4(oh)2 with oxygen to form fe(h20)3(oh)3?
    I am not sure about the oxidation one (if that's what you are looking for, the one when it's left in the air) but here is one that forms [Fe(H2O)3(OH)3]:

    [Fe(H2O)6]3+(aq) + 3OH(aq) ==> [Fe(H2O)3(OH)3](s) + 3H2O(l)
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    is ionic or covalent bonding stronger?
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    Hi,

    This question is about transition metal titration calculations. Part 6d on this paper
    http://filestore.aqa.org.uk/subjects...5-QP-JUN12.PDF

    I am unsure how the ratio is obtained. Could someone please walk me through it? I don't know if you're meant to take into account c2o4 and fe oxidising or just 1? If that makes sense

    Cheers

    Nvm figured it out.
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    Hey guys
    In the spec it says about knowing that Cr2O3 is a catalyst for the manufacturing of methanol from CO2 and Hydrogen.
    Have you guys expanded on this?
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    (Original post by zombaldia)
    Hi,

    This question is about transition metal titration calculations. Part 6d on this paper
    http://filestore.aqa.org.uk/subjects...5-QP-JUN12.PDF

    I am unsure how the ratio is obtained. Could someone please walk me through it? I don't know if you're meant to take into account c2o4 and fe oxidising or just 1? If that makes sense

    Cheers
    combine the bottom two equations to get FeC2O4 on one side and Fe3+ + 2co2 + 3e- on the other, then combine this with the first.
 
 
 
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