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A2 F335 OCR Salters B 2012 - Questions

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    Hi,

    Does anyone know how to answer questions 5.f.i and ii?

    As well as question 1.c.iii. If you go by the n+1 rule then you'd surely have a splitting value of 4 and then 2? How could it be zero both times?

    I cant seem to figure it out :s

    Here's a copy of the paper and mark scheme if you don't have it:
    http://www.thestudentroom.co.uk/show...3#post37931943

    Thank you
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    (Original post by TheStudent.)
    Hi,

    Does anyone know how to answer questions 5.f.i and ii?

    As well as question 1.c.iii. If you go by the n+1 rule then you'd surely have a splitting value of 4 and then 2? How could it be zero both times?

    I cant seem to figure it out :s

    Here's a copy of the paper and mark scheme if you don't have it:
    http://www.thestudentroom.co.uk/show...3#post37931943

    Thank you
    I've just done this paper so will write up some solutions in a second.
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    For 5) f) i)
    A student sets out to make a buffer solution. The student measures out 27 cm3 of
    0.050 mol dm–3 HA solution and reacts it with one-third of the volume of 0.10 mol dm–3 sodium
    hydroxide needed for complete neutralisation.

    HA + NaOH --------> NaA + H2O

    So first of all the moles of Acid HA.
    n = C X V / 1000
    n = (0.05 X 27) / 1000
    n = 1.35X10-3 moles

    As the volume added was a 1/3 of the require volume to neutralise, the amount of moles in the volume actually added will be the moles required / 3.

    So...
    actual n = (1.35X10-3) / 3
    actual n = 4.5X10-4

    V added = (n X 1000) / C where C is the concentration of sodium hydroxide

    V added = ( 4.5X10-4 X 1000) / 0.1
    V added = 4.5 cm3

    5))ii)
    Here you use a lot of the values you calculated above ^^^
    moles of HA added to the solution = 1.35X10-3 moles
    moles of A- added to the solution = 4.5X10-4 moles

    For part 2 I have 0.2 less than the mark scheme so going to have a quick check of the ol' solutions before I post this.


    And for 1)c) if you draw out the structure you'll find the there is in fact an oxygen between the CH3 and the H bonded to the oxygen. This there is no splitting.
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    (Original post by Mathlete 4 the win)
    For 5) f) i)
    A student sets out to make a buffer solution. The student measures out 27 cm3 of
    0.050 mol dm–3 HA solution and reacts it with one-third of the volume of 0.10 mol dm–3 sodium
    hydroxide needed for complete neutralisation.

    HA + NaOH --------> NaA + H2O

    So first of all the moles of Acid HA.
    n = C X V / 1000
    n = (0.05 X 27) / 1000
    n = 1.35X10-3 moles

    As the volume added was a 1/3 of the require volume to neutralise, the amount of moles in the volume actually added will be the moles required / 3.

    So...
    actual n = (1.35X10-3) / 3
    actual n = 4.5X10-4

    V added = (n X 1000) / C where C is the concentration of sodium hydroxide

    V added = ( 4.5X10-4 X 1000) / 0.1
    V added = 4.5 cm3

    5))ii)
    Here you use a lot of the values you calculated above ^^^
    moles of HA added to the solution = 1.35X10-3 moles
    moles of A- added to the solution = 4.5X10-4 moles

    For part 2 I have 0.2 less than the mark scheme so going to have a quick check of the ol' solutions before I post this.


    And for 1)c) if you draw out the structure you'll find the there is in fact an oxygen between the CH3 and the H bonded to the oxygen. This there is no splitting.
    Thanks for this!

    For all those calculations, I still can't believe question 5.f.i was only one mark. Seems pretty harsh to be honest!

    Why is there no splitting? :confused: wouldn't the CH3 have to split from the O atom?
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    (Original post by TheStudent.)
    Thanks for this!

    For all those calculations, I still can't believe question 5.f.i was only one mark. Seems pretty harsh to be honest!

    Why is there no splitting? :confused: wouldn't the CH3 have to split from the O atom?
    Only adjacent hydrogens next to the CH3 cause splitting, because oxygen isn't hydrogen, it doesn't split anything =]


    This was posted from The Student Room's iPhone/iPad App
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    (Original post by TiTo20)
    Only adjacent hydrogens next to the CH3 cause splitting, because oxygen isn't hydrogen, it doesn't split anything =]


    This was posted from The Student Room's iPhone/iPad App
    We were never taught that :eek: but anyways thank youuuuuu! it all makes sense now lol.

    Good luck for next wednesday guys!
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    Does anyone have the Jan 2012 F335 and F334 paper and mark scheme ?
    Thanks alot
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    (Original post by kishenp)
    Does anyone have the Jan 2012 F335 and F334 paper and mark scheme ?
    Thanks alot
    someones posted it above...read the thread first :P :P
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    Does anyone have the marksheme for June 2012 salters a2 f335 just done it today and am very anxious!

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