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Homework Help: Electrolysis question

  1. Nov 18, 2015 #1
    1. The problem statement, all variables and given/known data
    Electrolysis of an aqueous solution of copper(II) nitrate was carried out using copper electrodes. The mass of the anode decreased by 1.28 g while that of the cathode increased by 1.18 g
    Assuming that the copper anode contains silver and gold impurities, which statement is true?
    A. The blue colour of aqueous solution of copper(II) nitrate become darker
    B. 0.10 g of silver and gold were collected from the electrolysis
    C. The quantity of electricity used was 1790C
    D. 1.28 g of copper dissolved at the anode

    2. Relevant equations

    3. The attempt at a solution
    A and D should be wrong because the mass of copper dissolved at anode is lower than the mass of copper deposits at cathode
    While for C, Cu2++2e-->Cu
    2F = 1 mol of Cu
    x = 1.18/63.5 mol of Cu
    Therfore, x= 3586C
    So C should be wrong. But the answer is C
    As for B, I don't have a clue
  2. jcsd
  3. Nov 19, 2015 #2


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    Staff: Mentor

    You don't know that - assuming the anode made of pure copper more could dissolved than deposited. However, if it were only 50% copper less dissolved than deposited. So all we can say is that we don't know whether the amount of copper in the solution changed - and that eliminates A, B and D, but for a different reason than you thought,

    You are right about the charge required being 3.59×103 C, apparently whoever wrote the question forgot about factor of 2 (as the answer given is exactly half of the correct one).
  4. Nov 19, 2015 #3


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    Homework Helper
    Gold Member

    He writes a lot of the questions here. :oldwink: :oldbiggrin:
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