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    NH4Cl ----> (NH4+) + (Cl-)

    The NH4+ reacts reversibly with water to produce H3O+.
    But I think NH4+ is weaker than CH3COOH, so gives the lowest amount of H+ ?

    and NH3 is a weak base, so doesn't produce any H+
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    (Original post by SKK94)
    [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?
    Br- is not coloured, Br2 is coloured
    say if OH- is in excess, and reaction is completed
    using acid would be a good idea to titrate the unreacted alkali
    i think, thats how i make myself understood :P it may not be right
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    (Original post by Amila888)
    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 ?
    Isn't the answer B? Both HCl & NaCl dissociate completely... therefore Cl- amount doubles.... but volume doubles also so concentration stays the same



    (Original post by SKK94)
    [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?
    Br- is colourless... & the acid reacts with the OH- ... to form water so it stops the reaction



    Also to answer your next question about NH4Cl and ethenoic acid I think it was...
    ... if in doubt check in data booklet... stronger acids have higher dissociation constants
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    (Original post by SKK94)
    [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?
    Br- is a colourless ion in solution . Acid reacts with OH- ions.
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    the answer to that Cl- concentration is C .... i have no idea how it is true
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    (Original post by Amila888)
    the answer to that Cl- concentration is C .... i have no idea how it is true
    Really? I'm sure it's B!

    edit: oh for the lowest concentration of H+ yes it would be C because NH4Cl + NH3 forms an alkaline buffer?

    NH4Cl -> NH4+ + Cl-

    NH3 + H+ <--> NH4+

    I'm not sure actually :/
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    (Original post by jethacan)
    Really? I'm sure it's B!
    Pretty sure it is B too, C makes no sense... I think AS01 asked the same question yesterday & said it was B in the MS
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    (Original post by posthumus)
    Pretty sure it is B too, C makes no sense... I think AS01 asked the same question yesterday & said it was B in the MS
    I just realised it's asking for the lowest concentration of H+, it's not the same as the one yesterday
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    (Original post by jethacan)
    I just realised it's asking for the lowest concentration of H+, it's not the same as the one yesterday
    Lol I didn't even read the whole question, I assumed it was lol

    NH4Cl weak dissociation... other one has no Cl-
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    (Original post by StellaRawr11)
    Br- is not coloured, Br2 is coloured
    say if OH- is in excess, and reaction is completed
    using acid would be a good idea to titrate the unreacted alkali
    i think, thats how i make myself understood :P it may not be right

    (Original post by posthumus)

    Br- is colourless... & the acid reacts with the OH- ... to form water so it stops the reaction


    (Original post by Amila888)
    Br- is a colourless ion in solution . Acid reacts with OH- ions.
    Oh!
    Thanks!


    I'm off. Exam's 1.5 hours!
    Good Luck everyone
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    Ok then guys.. good luck to you all ! hoping for an easy paper ... Lets discuss this paper sum time later. u knw, after 48 hours i think.
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    Good luck everyone ! Speak to ya guys soon ...
    • Thread Starter
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    How did it go guys?

    Posted from TSR Mobile
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    (Original post by AS01)
    How did it go guys?

    Posted from TSR Mobile
    I thought it went fairly well, answered all the questions, feeling confident that I will at least improve my U from last time. I'm not too good at maths so it took me ages to work out how to convert pKa back to Ka so I could calculate the pH, but I got there eventually.
    Imagine my horror when I got to the last question and was missing my ruler!
    Luckily the data booklets provided were backed with card so I used that instead! :cool:

    Hope everyone else found it ok, it seemed a lot nicer than the January exam!
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    I thought the exam was pretty difficult..
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    (Original post by MrProff)
    I thought it went fairly well, answered all the questions, feeling confident that I will at least improve my U from last time. I'm not too good at maths so it took me ages to work out how to convert pKa back to Ka so I could calculate the pH, but I got there eventually.
    Imagine my horror when I got to the last question and was missing my ruler!
    Luckily the data booklets provided were backed with card so I used that instead! :cool:

    Hope everyone else found it ok, it seemed a lot nicer than the January exam!
    Ya I think it was alright I messed up order question again!
    The rest went good. Lol lucky you! We dont have those kind of data booklet. What do u think grade boundaries gonna be?

    Posted from TSR Mobile
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    (Original post by nnekaoke)
    I thought the exam was pretty difficult..
    I wouldnt say that the paper was easy and it was weird type! That ethanedioic acid question! Took me a while to figure out what the hell am I supposed to write lol

    Posted from TSR Mobile
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    (Original post by AS01)
    I wouldnt say that the paper was easy and it was weird type! That ethanedioic acid question! Took me a while to figure out what the hell am I supposed to write lol

    Posted from TSR Mobile
    I think once you realised it was just a weak acid but both ends could dissociate to give 2 H+ like sulfuric does, but when the sodium is added on one end it only dissociates one H+ i think, thats what I went on about anyway lol
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    (Original post by MrProff)
    I think once you realised it was just a weak acid but both ends could dissociate to give 2 H+ like sulfuric does, but when the sodium is added on one end it only dissociates one H+ i think, thats what I went on about anyway lol
    Yeah that's what it is but took me a while. Can u remember all of the question?
    I wanted more organic chem!

    Posted from TSR Mobile
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    (Original post by AS01)
    Yeah that's what it is but took me a while. Can u remember all of the question?
    I wanted more organic chem!

    Posted from TSR Mobile
    There was some stuff on that crazy long chemical..Sodium Hydrogenethanedioic acid maybe?

    I think with that the thing was it would have only donated one H+ in equilibria cos the other side was a methanoate group so wouldnt have affected it?
 
 
 
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