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OCR Chemistry F322~ 4th June 2013~ AS Chemistry Watch

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    Hard A= 72
    42
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    It was okay A= 76
    99
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    Easy A= 79
    75
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    Very Easy A=82
    60
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    (Original post by music144k)
    hey guys,
    what/how are we supposed to revise with the 'pre-release material' given?!

    What is pre-released material??... thank you
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    (Original post by OldSchoolTech)
    I try and think of them as equations.
    Once you know the M+ value, set this equal to the general formula then just evaluate to find n.

    If the compound was an alcohol with M+ of 60:
    General formula for alcohol CnH2n+1OH

    60 = CnH2n+1OH
    43 = CnH2n+1 (Subtracted 17=OH)
    42 = CnH2n

    CH2 = 14
    42/14 = 3 = n

    The put this pack into the general formula to get
    C3H7OH. (propanol)

    Then use other m/z peaks to determine if its propan-1-ol or 2-ol.

    Hope that made sense. Seems complicated but it works for me - just do loads of practice!!!


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    you are genius!
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    let's test eachother guys!
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    In questions that ask you to calculate enthalpy change of formation from combustion values, why does oxygen have a value of 0J?
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    (Original post by Anonymous1717)
    In questions that ask you to calculate enthalpy change of formation from combustion values, why does oxygen have a value of 0J?
    Because oxygen is an element already so the enthalpy change for the formation of an element from an element is zero.
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    (Original post by Anonymous1717)
    In questions that ask you to calculate enthalpy change of formation from combustion values, why does oxygen have a value of 0J?
    I think its because it doesnt take any energy to form oxygen. oxygen exists in its standard state of a gas, so to convert it into a gas takes no energy.
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    (Original post by Jacksgap)
    What is pre-released material??... thank you
    Oh, My teacher gave it to us and said we should revise from it..?
    (this is for OCR salters chemistry.. sorry im new here, not sure if im on right thread..?! :confused:)
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    (Original post by needtosucceed=))
    I think its because it doesnt take any energy to form oxygen. oxygen exists in its standard state of a gas, so to convert it into a gas takes no energy.
    Yess spot on...

    well done
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    (Original post by music144k)
    Oh, My teacher gave it to us and said we should revise from it..?
    (this is for OCR salters chemistry.. sorry im new here, not sure if im on right thread..?! :confused:)
    ah wrong thread, this is for the OCR A exam
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    (Original post by needtosucceed=))
    ah wrong thread, this is for the OCR A exam
    Oops!
    thanks! aha sorry if I confused any of you
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    I need to learn.. remember all the pesky facts
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    (Original post by Anonymous1717)
    In questions that ask you to calculate enthalpy change of formation from combustion values, why does oxygen have a value of 0J?
    You cannot combust oxygen so it will not have a combustion value
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    (Original post by Gotzz)
    Because oxygen is an element already so the enthalpy change for the formation of an element from an element is zero.
    So even though it is the combustion value they give we treat it like a formation value? :confused:
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    anyone revising for f324 and f325??

    I have concentrated so much time on this one, i am finally happy with ppq marks but i am slacking behind f324 and f325
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    (Original post by .raiden.)
    Enthalpy change = bond enthalpy of reactants - bond enthalpy of products

    So

    -184 = 679 - bond enthalpy of product

    Bond enthalpy of product = 679 + 184
    = 863

    BUT this is the bond enthalpy of 2HCL
    They ask for HCL so divide your answer by two. 431.5... 432 (3sf)

    Hope that helped
    Thanks so much, i understand it now
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    (Original post by Hello...)
    You cannot combust oxygen so it will not have a combustion value
    This is what I was thinking too!
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    (Original post by Hello...)
    200 Tonnes of Methane = 200,000,000g of Methane
    Moles=200,000,000/16
    =12500000 moles of Methane
    3 Moles of Hydrogen in the equation, therefore
    12500000 X 3=37500000 moles of hydrogen [THEORETICAL]

    In the question it says 68.4 tonnes of Hydorgen is produced
    68.4 tonnes = 68400000g of Hydrogen
    Moles= 68400000/2
    =34200000 moles of Hydrogen [ACTUAL]

    % Yield= (34200000/37500000) X 100
    =91.2%
    Sorry but why did u divide the hydrogen by two?



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    (Original post by zangorou)
    you are genius!
    Aha thanks, I'm glad it made sense :P
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    (Original post by 344302)
    Sorry but why did u divide the hydrogen by two?



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    Number of Moles= Mass/RMM
    RMM of hydrogen =2

    (Also i had already divided it by 1 and my overall answer was almost 200% so i knew I'd gone wrong somewhere)
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    (Original post by 344302)
    Sorry but why did u divide the hydrogen by two?



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    the molar mass of hydrogen
 
 
 
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