Question

Write the overall reactions taking place at the cathode in a lead accumulator cell during discharging of the cell.

Answer 1

The electrons produced at the anode travel through the external circuit and re-enter the cell at the cathode. At the cathode, PbO₂ is reduced to Pb²⁺ ions in the presence of H⁺ ions. Subsequently, Pb²⁻ ions so formed combine with SO²⁺ ions from H₂SO₄ to form insoluble PbSO₄ that gets coated on the electrode.

\[\ce{PbO_{(s)} + 4H+_{(aq)} + 2e- -> Pb^{2+}_{( aq)} + 2H2O_{(l)} (reduction)}\]
\[\ce{Pb_{(s)} + SO^{2-}_{4(aq)} -> PbSO4_{(s)} (precipitation)}\]
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\[\ce{PbO2 _{(s)} + 4H+_{( aq)} + SO^{2-}_{4(aq)} + 2e- -> PbSO4_{(s)} + 2H2O_{(l)}}\]