The operation and recharging of the lead-acid automobile battery involves two completely…

Chemistry · JEE Main · NTA ExamsRedox Reactions and Electrochemistry

The operation and recharging of the lead-acid automobile battery involves two completely reversible half-reactions.

\[\begin{array}{l} \mathrm{Pb}(5)+5 \mathrm{O}_{4}^{2-}(\mathrm{aq}) \longrightarrow \mathrm{PbSO}_{4}(5)+2 \mathrm{e}^{-} \\ \mathrm{PbSO}_{4}(5)+2 \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{PbO}_{2}(5)+4 \mathrm{H}^{+}+5 \mathrm{O}_{4}^{2-}+2 \mathrm{e}^{-} \end{array}\]

When a lead-acid battery is used to start a car, the anode reaction is

\(\mathrm{Pb}(5)+5 \mathrm{O}_{4}^{2-} \longrightarrow \mathrm{PbSO}_{4}(5)+2 \mathrm{e}^{-}\)

What are the cathode half reactions when this battery is being recharged?

  1. \(\mathrm{PbSO}_{4}(\mathrm{~s})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pb}_{(\mathrm{s})}+5 \mathrm{O}_{4}^{2-}(\mathrm{aq})\) 
  2. \(\mathrm{Pb}(5)+5 \mathrm{O}_{4}^{2-} \longrightarrow \mathrm{PbSO}_{4}(5)+2 \mathrm{e}^{-}\)
  3. \(\mathrm{PbO}_{2}(5)+4 \mathrm{H}^{+}(\mathrm{aq})+5 \mathrm{O}_{4}^{2-}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{PbSO}_{4}(5)+2 \mathrm{H}_{2} \mathrm{O}(I)\)
  4. \(\mathrm{PbSO}_{4}(5)+2 \mathrm{H}_{2} \mathrm{O}(I) \longrightarrow \mathrm{PbO}_{2}(5)+4 \mathrm{H}^{+}(\mathrm{aq})+5 \mathrm{O}_{4}^{2-}(\mathrm{aq})+2 \mathrm{e}^{-}\)

Answer

(C) PbO _ 2 (5)+4 H ^ + ( aq )+5 O _ 4 ^ 2- ( aq )+2 e ^ - PbSO _ 4 (5)+2 H _ 2 O (I)

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