[Sophie G]

a) Give the cell diagram notation of the electrochemical cell that could be used to determine experimentally the dissociation constant (Kw) of water. The standard reduction potential for

O2 + 2H2O + 4e- -> 4OH-   E=+0.40V

Calculate E° for this cell.

b) Use your value from part (a) to calculate the dissociation constant at 298 K.

I saw a later response, and after following what I thought was suggested, I came up with a number that seemed really off as well. I'd really appreciate any help you can give me!

This is what I've done so far..

O2 + 2H2O + 4e- -> 4OH-    E=+0.40V
2(H2 -> 2H+ + 2e-)       E=0.00V

O2+ 2H2O + 2H2 -> 4OH- + 4H+ (aq)  Ecell=+0.40V

ΔG=-4(9.65X10^4 J/K*mol)(0.40V)
    =-1.544X10^5

lnK=-ΔG/(RT)
    =(1.544X10^5J)/((8.3144J/K*mol)(298K)
    =63.695
k=4.6X10^27

This is way too high. I have a feeling it was with my initial cell work in a).

Thanks in advance for any help you can give, I'm pretty stumped.