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    This thread is for discussions for the upcoming Edexcel International A levels in January 2014 for chemistry unit 4.
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    Hi there,

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    Hey guys, the thread has been quiet...
    The exam is about a month away, anyone here doing Chemistry IAL this Jan?
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    Hi
    I am doing chemistry IAL and i am writing unit 4, unit 5 and unit 6b. Which ones are you taking?


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    (Original post by kcapsoccer)
    Hi
    I am doing chemistry IAL and i am writing unit 4, unit 5 and unit 6b. Which ones are you taking?


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    Hey,

    I'm doing unit 4 chem, phy and bio.
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    (Original post by Relaxedexams)
    Hey,

    I'm doing unit 4 chem, phy and bio.
    ohh nice! what topic are you finding the hardest in chem unit 4? i think that spectroscopy is the hardest one. :/


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    (Original post by kcapsoccer)
    ohh nice! what topic are you finding the hardest in chem unit 4? i think that spectroscopy is the hardest one. :/


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    I find organic chemistry to be rather annoying :P
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    yea spectroscopy and chromatography are a major pain in the conicals (the apparatus) , esp the environment/nmr bit :/
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    Good luck for anyone doing it today



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    you too lets hope we will all end up with good results!
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    Hi.

    For that section C sucrose question..they've said to comment on the effect on the extent of the reaction if temperature is increased.
    But my problem is that this reaction is not reversible, hence if it does take place it would go to completion right? So there would be no effect on the extent of the reaction? :dontknow:

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    (Original post by TheKingOfTSR)
    Hi.

    For that section C sucrose question..they've said to comment on the effect on the extent of the reaction if temperature is increased.
    But my problem is that this reaction is not reversible, hence if it does take place it would go to completion right? So there would be no effect on the extent of the reaction? :dontknow:

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    Yes, don't see where the mark lies.

    The titration graph was misleading imo, because even after adding 30cc of HCl the pH would still be higher than zero (by calculation). Why then did they extend the graph to negative pH and why ask the previous question??
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    the pH of 4 mol/dm3 of acid was about -0.6. So at the 30cc the pH of the soln would be -0.6
    The curve would touch the -0.6 pH mark at 30 cc
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    Would be glad if any one has the unofficial mark scheme or question paper for unit 4.
    And best
    of luck for unit 6
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    (Original post by TheKingOfTSR)
    Hi.

    For that section C sucrose question..they've said to comment on the effect on the extent of the reaction if temperature is increased.
    But my problem is that this reaction is not reversible, hence if it does take place it would go to completion right? So there would be no effect on the extent of the reaction? :dontknow:

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    I don't think the question was like that! I forgot the actual question. If you can tell me the actual question then maybe I can give you an answer.
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    (Original post by Labib)
    the pH of 4 mol/dm3 of acid was about -0.6. So at the 30cc the pH of the soln would be -0.6
    The curve would touch the -0.6 pH mark at 30 cc
    I don't think so.

    The number of excess mol of H ions at 30cc= 0.005 * 4 = 0.0020

    Therefore concentration of H ions = 0.020/0.055 = 0.3636363636

    pH at this point= 0.439

    So I guess it shouldn't be at -0.6 but should appear to approach it at that point
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    (Original post by Labib)
    the pH of 4 mol/dm3 of acid was about -0.6. So at the 30cc the pH of the soln would be -0.6
    The curve would touch the -0.6 pH mark at 30 cc
    No. :nah:

    pH of the solution is above that as only 5cc of acid is present in 55cc of solution.

    I guess as long as your graph isn't horizontal at the end and it ends above -0.6 then you'll get the mark.


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    (Original post by Labib)
    I don't think the question was like that! I forgot the actual question. If you can tell me the actual question then maybe I can give you an answer.
    Explain the effect, if any, of increasing the temperature on the system entropy change, the total entropy change and the extent of the reaction. (4)
    ^something worded like that.

    The combustion of sucrose isn't reversible, so how come "extent of the reaction "?
    If the reaction does take place, (kinetic inertness is overcomed) then it would go to completion right?

    Edit: not system but surrounding entropy change.
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    It was the surrounding entropy change and total entropy change..

    When temperature is increased obviously surrounding entropy change will decrease (because entropy change of surrounding = -deltaH/T)
    Since total entropy change = entropy change of surrounding + entropy change of system.. the value for total entropy change will decrease as well..
    however, the reaction will undergo completion as it's an exothermic reaction (so, despite what temperature the surrounding is positive) and the entropy change of system is also positive as disorderedness increases as products are formed...
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    (Original post by examman123)
    It was the surrounding entropy change and total entropy change..

    When temperature is increased obviously surrounding entropy change will decrease (because entropy change of surrounding = -deltaH/T)
    Since total entropy change = entropy change of surrounding + entropy change of system.. the value for total entropy change will decrease as well..
    however, the reaction will undergo completion as it's an exothermic reaction (so, despite what temperature the surrounding is positive) and the entropy change of system is also positive as disorderedness increases as products are formed...
    do you remember how many marks did that question have?


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