Reduction half-reactions with corresponding standard half-cell
potentials are shown below.
Zn2+(aq) + 2 e- ? Zn(s) E
Since Aluminium is above Zinc in the potentials:
Al is oxidized (anode) and Zn+2 is reduced
(cathode)
The e-s leave the Al electrode and flow to the Zn
electrode.
Oxidation: 2(Al0 ? Al+3 + 3e-)
Recution: 3(Zn+2 + 2e- ? Zn0)
Overall reaction: 2Al0 + 3Zn+2 + 6e- ? 6e- + 2Al+3 + 3Zn0
E cell = E ox + E red
E0cell = (1.66v) + (-0.76v*) = +0.90v
NOTE that the sign must be inverted *
Always change the sign of the reduction half-cell. All voltaic cells have positive voltage values.
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