[polly]

hi all,

I just need to know where to start if I had to calculate the pH of a solution given a potential of the solution relative to a standard hydrogen electrode?

any starting point would be good
Cheers

[Borek]

First of all - what solution, what electrode, what redox system?

If pH electrode - http://www.ph-meter.info/pH-electrode-potential

But if that's a platinum electrode and MnO₄^-/Mn²⁺ system situation is completely different.

[polly]

the exact question is as follows

Calculate the pH of a solution whose potential at 298K, measured with a standard hydrogen electrode at atmospheric pressure of 1.012 atm.(corrected for the vapour pressure of water at 298K) is -0.324V (vs. NHE)

I have only the Nernst equation as notes but nothing on how to work out the pH as asked in this question. No idea what is meant by NHE either.

No idea where to begin.

Thanks

[Borek]

NHE = Normal Hydrogen Electrode.

Nernst equation can be easily modified to contain pH (hint: think about the pH definition).

[polly]

Hi Borek, ok I did what you asked..., can you please tell me if the following answer is correct?

the cell potential of the solution is measured in reference to the SHE, which has a value of 0 by definition.

using                                          E(cell) = -0.0592 log[H⁺]

and thus,                                    pH =E(cell) / -0.0592 = -0.324 / -0.0592 = 5.47

Is this correct?

Thanks a lot.