Q3 / 150 · MHT CET 2025 (26 Apr Shift 1) · Chemistry

Which of the following changes takes place at positive electrode during recharging of lead accumulator?

  • A
    Pb is oxidised to $\mathrm{PbSO}_4$
  • Correct answer
    B
    $\mathrm{PbSO}_4$ is oxidised to $\mathrm{PbO}_2$
  • C
    $\mathrm{PbSO}_4$ is reduced to Pb
  • D
    $\mathrm{PbO}_2$ is reduced to $\mathrm{PbSO}_4$

Solution

The lead accumulator's recharging process involves reversing the discharge reactions. During discharge, the positive electrode (cathode) undergoes reduction:
$\mathrm{PbO}_2(s) + \mathrm{SO}_4^{2-}(aq) + 4\mathrm{H}^+(aq) + 2e^- \rightarrow \mathrm{PbSO}_4(s) + 2\mathrm{H}_2\mathrm{O}(l)$

Upon recharging, this electrode becomes the anode. The reverse oxidation reaction occurs:
$\mathrm{PbSO}_4(s) + 2\mathrm{H}_2\mathrm{O}(l) \rightarrow \mathrm{PbO}_2(s) + \mathrm{SO}_4^{2-}(aq) + 4\mathrm{H}^+(aq) + 2e^-$

This corresponds to oxidation of $\mathrm{PbSO}_4$ to $\mathrm{PbO}_2$, matching option B.

Hence, the correct answer is option: 'B'.

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