7th Edition 6L.5

[Angela Grant 1D]

This question asks for the cell diagrams of given skeletal equations. For (b) Ce4+ (aq) + I- (aq) --> I2 (s) + Ce3+ , I understand that the cell diagram would need a Pt (s) on the cathode end where Ce4+ reduces to Ce3+, so it'd be Ce4+(aq), Ce3+(aq) | Pt(s). But the answer key also has a Pt(s) on the anode end where I- is oxidized to I2. I thought Pt(s) wouldn't be needed since I2 is a solid. Can someone explain this please?

[Chem_Mod]

You are correct that I₂ is a solid, however that does not mean it is a conduction solid, ie a metal. I₂ is a solid but it is an insulator and as such would not conduct electricity as an electrode, so you need some other type of electrode to conduct the electrons that are being produced. This is why we add platinum.