A voltaic cell is constructed from a half-cell in which an aluminum rod dips into a solution of aluminum nitrate, Al(NO3)3, and another half-cell in which a lead rod dips into a solution of lead(II) nitrate, Pb(NO3)2. The two half-cells are connected by a salt bridge. Aluminum metal is oxidized during operation of the voltaic cell. What is the half-reaction that occurs at the cathode?
Pb(s) ? Pb2+(aq) + 2e-
Pb2+(aq) + 2e- ? Pb(s)
Al(s) ? Al3+(aq) + 3e-
Al3+(aq) + 3e- ? Al(s)
Al(s) + 3e- ? Al3-(aq)