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Homework Help: Electrolysis in Cu/Hg electrolytic cell

  1. Oct 28, 2007 #1
    1. The problem statement, all variables and given/known data

    http://img143.imageshack.us/img143/7135/electrolysisrf2.jpg [Broken]

    What is the ratio of number of moles of copper deposited to the number of moles of mercury deposited? {n(Cu):n(Hg)}

    2. The attempt at a solution

    Well the species present are;
    Cu^{2 + } /SO_4 ^{2 - } \;ions \\
    Hg_2 ^{2 + } /NO_3 ^ - \;ions \\
    and\;H_2 O \\

    so reading down the Eo table from left to right; the first species found is [tex]Cu^{2 + }[/tex] ions.
    So at the cathode we have; [tex]Cu^{2 + } + 2e^ - \to Cu[/tex]

    Now reading up the Eo table from right to left; the first species found is [tex]Hg_2 ^{2 + }[/tex]
    So I would assume that at the anode we have; [tex]Hg_2 ^{2 + } \to 2Hg^{2 + } + 2e^ - [/tex]

    Now the question states that it is the ratio of copper to mercury produced. How can this be?
    Do I just assume that the mercury ions are now further electrolysed to mercury by;
    [tex]Hg^{2 + } + 2e^ - \to Hg_{(l)}[/tex]

    Could someone please explain how this works and what rules I am supposed to be following as I am a little confused ...

    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Oct 29, 2007 #2

    - sorry I have an exam Friday :(
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