Q14 / 160 · TS EAMCET 2015 · Chemistry
A lead storage battery is discharged. During the charging of this battery, the reaction that occurs at anode, is
- A$\mathrm{PbSO}_4(\mathrm{~s})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pb}(\mathrm{s})+\mathrm{SO}_4^{2-}(\mathrm{aq})$
- Correct answerB$\mathrm{PbSO}_4(\mathrm{~s})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{I}) \longrightarrow$ $\mathrm{PbO}_2(\mathrm{~s})+\mathrm{SO}_4^{2-}(\mathrm{aq})+4 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{e}^{-}$
- C$\mathrm{PbSO}_4(\mathrm{~s}) \longrightarrow \mathrm{Pb}^{2+}(\mathrm{aq})+\mathrm{SO}_4^{2-}(\mathrm{aq})$
- D$$ \begin{array}{r} \mathrm{PbSO}_4(\mathrm{~s})+2 \mathrm{H}_2 \mathrm{O}(l)+2 \mathrm{e}^{-} \overrightarrow{\mathrm{PbO}_2(\mathrm{~s})}+\mathrm{SO}_4^{2-}(\mathrm{aq})+2 \mathrm{H}^{+}(\mathrm{aq}) \end{array} $$
Solution
During recharging, the cell is operated like an electrolytic cell. The electrode reactions are the reverse of those that occur during discharge.
At cathod
$$
\mathrm{PbSO}_4(s)+2 e^{-} \longrightarrow \mathrm{Pb}(s)+\mathrm{SO}_4^{2-}(\mathrm{aq})
$$
At anode $\mathrm{PbSO}_4(s)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow$
$$
\mathrm{PbO}_2(s)+\mathrm{SO}_4^{2-}(\mathrm{aq})+4 \mathrm{H}^{+}(\mathrm{aq})+2 e^{-}
$$
Net reaction
$$
\begin{aligned}
& 2 \mathrm{PbSO}_4(s)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow \\
& \mathrm{Pb}(s)+\mathrm{PbO}_2(s)+4 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{SO}_4^{2-}(\mathrm{aq})
\end{aligned}
$$
Hence, the correct answer is option: 'B'.