[bowersst]

can someone show me how to use the nerst equation? I have about 30 of these questions, but I don't feel like posting all of them here. I will just post this one, and hopefully I can figure out the rest from it.

 What is the pE value in a solution in equilibrium with air (21% O2 by volume) at pH 6.00?

^The main part of my confusion involves the fact that there are different versions of the nernst equation, and I also don't know which parts are supposed to come from a book, and other need calculating.

[Donaldson Tan]

use the nerst equation for electrochemistry. it relates electrode potential to concentration of reduced and oxidised species.

[Demotivator]

use the nerst equation for electrochemistry. it relates electrode potential to concentration of reduced and oxidised species.

The nernst equation can be  used for any redox process to calculate potential for reaction.

E = E(0) + (RT/nF)ln([oxidized]/[reduced])
For standard temp, RT/F is a constant, and converting ln to log yields:
E = E(0) + (.0591/n)log([oxidized]/[reduced])
The standard reduction half rxn (from tables) is:
4H+ + O2(g)  + 4e -> 2H2O  E(0) = 1.23 V
The oxidized part [oxidized] of the equation is:
([H+]^4 [pO2]
The [reduced] part is [H2O]^2 but it is not included because it is the solvent. n=4 (# of e)

E = 1.23 + (.0591/4)log([H+]^4 [pO2])
where [H+] = 10^-6 because ph=6
and pO2(g) = 0.21 atm  because that's the partial pressure of oxygen since it's 21% by volume.

then
E = 1.23 + (.0591/4)log([10^-6]^4 [0.21])
E= 1.23 - .36 = .87 V
PE = -log(E) = -log(.87) = .06