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Homework Help: Cell Potentials

  1. May 21, 2012 #1
    1. The problem statement, all variables and given/known data
    Calculate the cell potential at 25°C for the cell:

    Fe (s) | (Fe^2+ (0.100 M) || Pd^2+ (1.0*10^-5 M) | Pd (s)

    given that the standard potential for Fe^2+/Fe is -0.45 V and for Pd^2+/Pd is +0.95 V.

    A. +1.28 V
    B. +1.16 V
    C. +1.52 V
    D. +1.68 V

    2. Relevant equations
    E Cell potential = E Cathode - E Anode

    3. The attempt at a solution
    By looking at the two potentials for Fe and Pd, I deducted that the species at the cathode was Pd because 0.95 > -0.45. Then, I took the difference:

    E Cell potential = E Cathode - E Anode
    E Cell Potential = 0.95 - (-0.45)
    E Cell potential = 1.40 V (which isn't even an answer choice)

    However upon looking at answer choices and the answer key, the answer was in fact A. +1.28 V; can someone explain to me what went wrong in my calculations? Or if there is a typo?
  2. jcsd
  3. May 21, 2012 #2


    User Avatar

    Staff: Mentor

    Solutions are not in a standard state - you have to correct for concentrations using Nernst equation.
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