Question

From the following reduction potentials, determine the reduction potential of SN^4+ + 4e^- --> Sn^o

SN^2+ + 2e^- --> Sn^o | -0.135V
SN^4+ + 2e^- --> Sn^2+ | -0.15V

Step-by-step please.

Answer 1

To Scott
Please take another look at your calculation in line with this link. I believe the answer is about 0.14. When calculating a half cell potential from two other half cell potentials one cannot simply add the two. This link talks about the why.
https://chemistry.stackexchange.com/questions/9454/deriving-a-reduction-potential-from-two-other-reduction-potentials

I use a short cut that cuts out some of the intermediate steps.
(n1E1 + n2E2)/(n1+n2)

Answer 2

oops ... thanks for the tip