Standard Reduction Potential Changes in Regards to Acidity

[Teemo]

Homework Statement

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?

O_2(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.

Homework Equations

Nernst Equation

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.

 

[Borek]

quotient would be 0, since there is only a pure liquid on the product side

Activity of a pure substance is not zero.

 

[Teemo]

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

 

[Borek]

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

 

[Teemo]

Thank you so much!