Chemistry of Batteries
Dry Cells
Anode (oxidation):
Zn(s) Zn2+(aq) + 2 e-
Cathode (reduction):
2 MnO2 (s) + 2 NH4+(aq) + 2 e- Mn2O3 (aq) + 2 NH3 (aq) + H2O(l)
ammonia is tied up with Zn2+
Zn2+(aq) + 2 NH3 (aq) + 2 Cl-(aq) Zn(NH3)2Cl2 (s)
Overall (cell) reaction:
2 MnO2 (s) + 2NH4Cl(aq) + Zn(s) Zn(NH3)2Cl2 (s) + H2O(l) +Mn2O3 (s)
Ecell = 1.5 V
Alkaline Battery
Anode (oxidation):
Zn(s) + 2 OH-(aq) ZnO(s) + H2O(l) + 2 e -
Cathode (reduction):
MnO2 (s) + 2 H2O(l) + 2 e - Mn(OH)2 (s) + 2 OH -(aq)
Overall (cell) reaction:
Zn(s) + MnO2 (s) + H2O(l) ZnO(s) + Mn(OH)2 (s) Ecell = 1.5 V
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