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Standard Reduction Potential Changes in Regards to Acidity

  1. Apr 17, 2015 #1
    1. The problem statement, all variables and given/known data
    The reduction of O2 to H2O in acidic solution has a standard reduction potential of +1.23 V. What is the effect on the half-cell potential at 25 °C when the pH of the solution is increased by one unit?

    O2(g) + 4H+(aq) + 4e- –> 2 H2O(l)

    (A) The half-cell potential decreases by 59 mV.
    (B) The half-cell potential increases by 59 mV.
    (C) The half-cell potential decreases by 236 mV.
    (D) The half-cell potential increases by 236 mV.

    2. Relevant equations
    Nernst Equation

    3. The attempt at a solution
    I'm aware this is a Nernst equation problem. Yet, I'm not exactly sure how to apply it. It appears to me that the reaction quotient would be 0, since there is only a pure liquid on the product side. As such, I am not sure how to approach the problem.
     
  2. jcsd
  3. Apr 17, 2015 #2

    Borek

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    Staff: Mentor

    Activity of a pure substance is not zero.
     
  4. Apr 17, 2015 #3
    Would it be 1? I feel like I'm missing something obvious o_O
     
  5. Apr 17, 2015 #4

    Borek

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    Staff: Mentor

    Yes, it is 1. Just like activity of solids (think Ksp - it doesn't contain solid, as its activity is 1).
     
  6. Apr 17, 2015 #5
    Thank you so much!
     
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