Stuck on Analytical Chemistry Problem

Jul 2012
Hi all,

I'm stuck. Here's the question. Calculate the electrode potential of a platinum electrode immersed in a solution that is,

.075 M in Fe2(SO4)3 and .06 M in FeSO4?

It seems to me this is a cell where Fe2+ gets oxidized to Fe3+ and Sulfate gets reduced to H2SO3. Thus,

anode: 2Fe2+ <--> 2Fe3+ + 2e-; Eo= .771
cathode: (SO4)-2 + 4H+ + 2e- <---> H2SO3 + H2O; Eo = .172

The potential, E, would be the difference betweeen the two,

E = .172 - .0592/2 log 1/[SO4] + .771 + .0592/2 log [Fe2+]^2/[Fe3+]^2


But this is doesn't get the right answer. Any suggestions?