Solubility and redox reactions

[Samantha Chung 4I]

In the 7th edition, question 6N.1, I was wondering if we would be expected to know how to write a reaction for a solubility reaction such as AgCl -> Ag+ and Cl- ? How do we determine which one is oxidized/reduced? Also how do we know what reaction to look out for in the appendix?

[Tarika Gujral 1K]

For precipitates in general the form is:

REDUCTION: Precipitate + e — ions
OXIDATION: Ions — Precipitate

One ion will not change charge, (for AgCl) Cl- retains an oxidation number of -1, so the other ion is the one that is undergoing oxidation or reduction (the one that is going from solid to +1)

The way you determine which reaction is undergoing oxidation or reduction for a galvanic cell is to evaluate overall cell potential. E must be greater than zero.