# Standard Reduction Potential Changes in Regards to Acidity

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1. Apr 17, 2015

### Teemo

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. Apr 17, 2015

### Staff: Mentor

Activity of a pure substance is not zero.

3. Apr 17, 2015

### Teemo

Would it be 1? I feel like I'm missing something obvious

4. Apr 17, 2015

### Staff: Mentor

Yes, it is 1. Just like activity of solids (think Ksp - it doesn't contain solid, as its activity is 1).

5. Apr 17, 2015

### Teemo

Thank you so much!