14.13 [ENDORSED]

[Michelle_Tan_1G]

The cell diagram, in the solution, uses Pt electrodes instead of the oxidized solid (I2). I'm not sure when to add those in. Do we use Pt(s) as electrodes when there are no metals oxidized/reduced?

[Chem_Mod]

Inert electrodes such as platinum or graphite are necessary in cases where a surface for reaction is necessary. This can happen in gas/ion electrode cells or in cells where there is no solid electrode present. In 14.13, there is no solid except for I₂ (s). However, when you study the half reactions, you see that iodine anions are actually oxidized since the standard reduction potential for I₂ (s) + 2e^- --> 2I^- (aq) is "less positive" than the standard reduction potential for Ce⁴⁺ (aq) + e^- --> Ce³⁺ (aq). The solid iodine has to deposit on something, so we use an inert electrode such as platinum for both electrodes in this cell.