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    Nernst equation

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    Here is the question:

    Q: Show with the aid of a form of the Nernst equation that when using a pH sensitive glass electrode and reference electrode that the measured potential is proportional to pH.

    This is the answer I have:

    Nernst equation:

    E = E ° - 0.059/n * log Q

    Q is the reaction quotient, active mass of products divided by active mass of reactants.

    The glass electrode half reaction can be written as
    H2 -----> 2H(+) + 2e(-)
    Substituting in the Nernst equation we have
    E = E° - 0.059/2 * log [H+]2 / [H2]

    At constant H2, also we know E° is zero. So,
    E = -0.059/2 * log [H+]2
    E = -0.059 * log [H+]
    E = 0.059 * pH

    Thus, E is directly proportional to the pH of the solution, as -log[H+] is defined to be pH

    Is this correct? How is E = E ° - 0.059/n * log Q deduced from E = E ° - (RT/nF)lnQ

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    Solution Preview

    You are correct,

    How is E = E ° - 0.059/n * log Q deduced from E = E ° - (RT/nF)lnQ

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    Solution Summary

    This solution examines a problem solved using the Nernst equation and assesses its accuracy.