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Nerst Equation

  1. Apr 30, 2007 #1
    1. The problem statement, all variables and given/known data
    What is the concentration of the unknown Cu2+ solution?
    The reaction is Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s).
    The concentration of Zn2+ is 0.05 M

    2. Relevant equations

    3. The attempt at a solution
    I'm coming up with about 2 different answers, and I'm not sure which is correct.
    Using a graph of (Emf vs log Cu2+) I obtained the line y = -1.0967 - 0.02x and I'm not sure how to figure out the unknown copper concentration.

    Method 1 (I'm leaning towards this method):
    -1.08 V is the voltage obtained from the unknown.
    -1.08 V = -1.0967 - 0.02x
    x = -.835
    10^x = 10^-.835

    [Cu2+] = .146 M

    Method 2:
    I'm assuming E0 is the y intercept and -0.0592/2logQ is the slope, not positive if that is correct.
    E = E0 - 0.0592/2logQ
    Q = [Zn2+]/[Cu+2]
    -1.08 = -1.0967 - 0.0592/2 log Q
    [Cu+2] = .183 M

    Which is the correct method to use for finding the copper concentration?
    Last edited: Apr 30, 2007
  2. jcsd
  3. May 1, 2007 #2


    User Avatar

    Staff: Mentor

    For both metals you have E = E0 + 0.0296 log [Me+2]

    Just compare and put correct E0 values in, you will get one equation with one unknown.
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