Chapter 5, Problem 5.17E

The tarnish of silver objects is a coating of silver sulfide $\left({\text{Ag}}_{\text{2}}\text{S}\right)$, which can be removed by putting the silver in contact with aluminum metal in a dilute solution of baking soda or salt. The equation for the cleaning reaction is

${\text{3Ag}}_{\text{2}}\text{S}\left(\text{s}\right)+\text{2Al}\left(\text{s}\right)\to \text{6Ag}\left(\text{s}\right)+{\text{Al}}_{\text{2}}{\text{S}}_{\text{3}}\left(\text{s}\right)$

The sulfur in these compounds has a $-2$ oxidation number. What are the oxidizing and reducing agents in the cleaning reaction?