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    (Original post by posthumus)
    There's so much we don't need to know lol :eek: (Damn george :mad: )

    I have far less time this time for unit 5.... so I might abandon george and just use revision guides..

    Well anyway I am off to get some sleep now

    Good luck AS01 with your exam tomorrow... & speak to ya soon Thanks for all the questions also you've asked me (I have learnt a lot, imagine brady's came up tomorrow )

    And good luck to everyone else too who reads this ! May speak to some of you tomorrow morning
    Hey man.. wanna revise together? why does the PH of a strong acid increase by one unit when diluted by a factor of 10, where as a weak acid PH increases by 0.5?
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    (Original post by Amila888)
    Hey man.. wanna revise together? why does the PH of a strong acid increase by one unit when diluted by a factor of 10, where as a weak acid PH increases by 0.5?
    Mind if I answer?
    Lol ,don't know the reason for the strong acid, but for the weak one, is it because the addition of water suppresses the dissociation of the weak acid?
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    (Original post by Amila888)
    Hey man.. wanna revise together? why does the PH of a strong acid increase by one unit when diluted by a factor of 10, where as a weak acid PH increases by 0.5?
    Ah not sure on how to explain this exactly But the H+ ions emitted from weak acid was already very suppressed

    where as stronger acids dissociate more.... so dilution would have a much larger

    Define lattice enthalpy & also how it effects entropy
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    Can someone please tell me in jan 11 q20 part a how is the peak Q for an OH group..theres no OH group in esters?
    :dontknow::dontknow:
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    (Original post by posthumus)
    Ah not sure on how to explain this exactly But the H+ ions emitted from weak acid was already very suppressed

    where as stronger acids dissociate more.... so dilution would have a much larger

    Define lattice enthalpy & also how it effects entropy
    The enthalpy change occured when 1 mol of solid compund is broken to form 1 mol of each scattered gaseous ions.

    A greater lattice enthalpy shows that the lattice is stronger. the bonds are stringer between ions. So, there is less entropy in a compound with higher lattice enthalpy... ?? :confused: i guess
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    (Original post by AT95)
    Can someone please tell me in jan 11 q20 part a how is the peak Q for an OH group..theres no OH group in esters?
    :dontknow::dontknow:
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    the peak of -OH groups in alcohols go from 3200-3750 according to the Data Booklet. this peak fits the scene right..
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    In reactions with weak bases and water, NH3 + H20 <----> NH4+ + OH-

    Why is [H2O] NOT in the Kb equation?
    Isn't it a reactant because it protonates the ammonia? :confused:
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    why is this forum not much active like the others... :confused: less people doing unit4..?
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    (Original post by Amila888)
    why is this forum not much active like the others... :confused: less people doing unit4..?
    I think most follow this thread ? http://www.thestudentroom.co.uk/show....php?t=2372695
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    (Original post by SKK94)
    In reactions with weak bases and water, NH3 + H20 <----> NH4+ + OH-

    Why is [H2O] NOT in the Kb equation?
    Isn't it a reactant because it protonates the ammonia? :confused:
    I think it's because the concentration of water is (almost) constant so Kb is the Kc for the reaction multiplied by the concentration of water to make the constant Kb. I hope that makes sense!

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    (Original post by SKK94)
    In reactions with weak bases and water, NH3 + H20 <----> NH4+ + OH-

    Why is [H2O] NOT in the Kb equation?
    Isn't it a reactant because it protonates the ammonia? :confused:
    Just like Ka.. we donot write H20. we actually get the term Ka or Kb because we kinda " leave out" the H20. or else it would be the same as Kc.
    Reason is the concentration of H20 is virtually constant.
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    (Original post by Amila888)
    The enthalpy change occured when 1 mol of solid compund is broken to form 1 mol of each scattered gaseous ions.

    A greater lattice enthalpy shows that the lattice is stronger. the bonds are stringer between ions. So, there is less entropy in a compound with higher lattice enthalpy... ?? :confused: i guess
    It's the opposite when 1 mole of solid is formed from it's gaseous ions!

    What you said is correct for negative enthalpy Which is what we use to work out enthalpy of solution

    I was expecting you to just quote equations, but I think what you said is correct It's also an endothermic process (breaking the lattice)... therefore makes entropy of surrounding more negative and does not favor dissolving

    How would you make margarine ? Give me 2 methods, their disadvantage & advantages!
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    (Original post by jethacan)
    I think it's because the concentration of water is (almost) constant so Kb is the Kc for the reaction multiplied by the concentration of water to make the constant Kb. I hope that makes sense!

    Posted from TSR Mobile

    (Original post by Amila888)
    Just like Ka.. we donot write H20. we actually get the term Ka or Kb because we kinda " leave out" the H20. or else it would be the same as Kc.
    Reason is the concentration of H20 is virtually constant.
    Oh I get it now! (Y)
    Thanks
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    (Original post by posthumus)
    It's the opposite when 1 mole of solid is formed from it's gaseous ions!

    What you said is correct for negative enthalpy Which is what we use to work out enthalpy of solution

    I was expecting you to just quote equations, but I think what you said is correct It's also an endothermic process (breaking the lattice)... therefore makes entropy of surrounding more negative and does not favor dissolving

    How would you make margarine ? Give me 2 methods, their disadvantage & advantages!

    one method is surely Hydrogenation of polyunsaturated and monounsaturated fats . Advantages - i have no idea
    Disadvantages- health problems ...
    wats the other method???
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    (Original post by Amila888)
    one method is surely Hydrogenation of polyunsaturated and monounsaturated fats . Advantages - i have no idea
    Disadvantages- health problems ...
    wats the other method???
    Transesterification
    A catalyst is added with some stearic acid to vegetable oil. The less unsaturated triglycerides are replaced.

    Advantage: no trans fatty acids are produced
    Disadvantages: Some stearic acid goes onto middle carbon of the triol (harmful to health)


    Partial hydration doesn't intefere with the order of the fatty acids on the triol however they weaken the C=C bond to active sites on catalyst therefore molecule rotation decreases (increases colestrol)

    How is biodisel produced ?
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    (Original post by posthumus)
    Transesterification
    A catalyst is added with some stearic acid to vegetable oil. The less unsaturated triglycerides are replaced.

    Advantage: no trans fatty acids are produced
    Disadvantages: Some stearic acid goes onto middle carbon of the triol (harmful to health)


    Partial hydration doesn't intefere with the order of the fatty acids on the triol however they weaken the C=C bond to active sites on catalyst therefore molecule rotation decreases (increases colestrol)

    How is biodisel produced ?
    from triglycerides in vegetable oil/animal fats. the same process : transesterification.
    hmm wat kind of questions could they ask from this area? i'v never seen any in the pastpapers.
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    (Original post by Amila888)
    from triglycerides in vegetable oil/animal fats. the same process : transesterification.
    hmm wat kind of questions could they ask from this area? i'v never seen any in the pastpapers.
    Maybe they wouldn't I knew everything word to word on this bit, from george facer book in January... now I barely know anything !

    I'm hoping section C will be entropy or equilibria
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    haha.. yea.. usually section C is either one of that or NMR . But i'd prefer NMR.. hope it gets easy. Nothing against Equlibria and entropy though, but they could ask us for some twisted explanations.. I dont think they could do that with NMR.
    anyway, its taking a long time for these stuff to get posted here right... :confused:
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    9. This question concerns four solutions, A to D. They were prepared by mixing equal
    volumes of 0.2 mol dm–3 solutions of two different substances. The substances were
    A HCl(aq) and NaOH(aq)
    B HCl(aq) and NaCl(aq)
    C NH3(aq) and NH4Cl(aq)
    D CH3COOH(aq) and CH3CO2Na(aq)
    Select, from A to D, the mixture which would:
    (a) have the lowest concentration of hydrogen ions ??

    The answer is C.. but why ?
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    [Jan 2013]
    Methods for investigating reaction rates include
    A colorimetry
    B collecting and measuring the volume of a gas
    C quenching, followed by titration with acid
    D quenching, followed by titration with iodine solution.
    Which method would be most suitable to investigate the rate of the following
    reactions?
    (b) C4H9Br(l) + OH−(aq) C4H9OH(l) + Br−(aq)

    The answer is C
    Why is colorimetry not used for this? I thought Br- was coloured?
    And what does the acid react with in the titration?
 
 
 
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