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Homework Help: Please Help Me With An Electrochemical Cell and Equivalence.

  1. Jan 27, 2014 #1

    Please don't be spooked by the long post, it's just that it contains two problems (I beg your pardon if I shouldn't have put both in one post, I just figured it'll be better than creating two posts...).

    I can't figure how to solve these, so if you please could please help me with either one or both... I greatly appreciate any help and will learn from any extent of assistance.

    1. The problem statement, all variables and given/known data

    Problem 1:

    An electrochemical cell is given, one containing an 0.1M CuSO4 solution and the other one containing an 0.1M ZnSO4 solution.

    Then, the Cu ion concentration is decreased by adding an Ammonia solution NH4OH into the CuSO4 cell, this triggers the following reaction:

    Cu{2+} (aq) + 4NH4OH <---> Cu(NH3)4{2+} + 4H2O

    {+} denotes charge.

    The reaction above decreases the Cu concentration since the complex ion Cu(NH3)4{2+} does not participate in the overall redox reaction of the cell.


    If the volume of each of the solutions (CuSO4, ZnSO4) is 100 cubic centimeters, calculate the Voltage of the cell after 5 ml of 5M NH4OH are added to the CuSO4 cell..?

    Problem 2:

    The equivalent of Sulfur Tri-oxide S2O3{2-} equals 1 mole of the same.

    Given the two reactions:

    2H{+} (aq) + 2I{-} (aq) + H2O2 ---> I2 (s) + 2H2O

    I2 + 2S2O3{2-} ---> 2I{-} + S4O6{2-}

    {-/+} denotes charge.


    Calculate how many moles of H2O2 will be produced from/react with 1 ml 0.1N S2O3{2-} ?

    N as in Normality, not M, Molarity.
    The reason it says “produced from/react with”, is because the question is translated, and does not explain this exactly in the original form... Please see if you can do anything with that, it will definitely help me learn if I see any progress with this...

    2. Relevant equations

    3. The attempt at a solution

    Stuck at beginning - not sure how to start, so please help me if you can, or at least kindly point me at the right direction.

    Thank you very much!!!
  2. jcsd
  3. Jan 27, 2014 #2


    User Avatar

    Staff: Mentor

    Do you know the Nernst equation?

    Thiosulfate, not sulfur trioxide.

    If equivalent equals mole, N=M.

    And yes, you should post two separate threads. Plus, you should show your efforts.
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