You are working in the research laboratory of a company developing new forms of batteries for installation in satellites. As a part of your investigation, you have decided to study various combinations of metal electrodes. The standard potential of a Zn²⁺/Zn electrode is 20.76 V, and the standard potential of the cell Zn(s)|Zn²⁺(aq)||Sn⁴⁺(aq),Sn²⁺(aq)|Pt(s) is 10.91 V. What is the standard potential of the Sn⁴⁺/Sn²⁺electrode?

ANTICIPATE Because the cell potential is positive, the right-hand electrode (tin) is the cathode, the site of reduction. Therefore the zinc couple is more strongly reducing than the tin couple, and it has the more negative value. In other words, expect the tin couple to be less negative (more positive) than 20.76 V.

PLAN To determine the standard potential of an electrode from the potential of a standard cell in which the other electrode has a known standard potential, use Eq. 1 rearranged into E_R° = E_cell° + E_L°.