Question

Which of the following is TRUE in case of recharging a Lead Storage Battery?

• A. $PbS{O}_4\left(s\right)+2e^{-}\to Pb\left(s\right)+S{O}_4^{2-}\left(aq\right)$
• B. $PbS{O}_4\left(s\right)+2H_{2}O\to Pb{O}_2\left(s\right)+S{O}_4^{2-}\left(aq\right)+4H^{+}\left(aq\right)+2e^{-}$
• C. $Pb\left(s\right)+S{O}_4^{2-}\left(aq\right)\to PbS{O}_4\left(s\right)+2e^{-}$
• D. $Pb{O}_2\left(s\right)+S{O}_4^{2-}+4H^{+}\left(aq\right)+2e^{-}\to PbS{O}_4\left(s\right)+2H_{2}O\left(l\right)$

Answer 1

Answer: (A), (B)

$PbS{O}_4\left(s\right)+2H_{2}O\to Pb{O}_2\left(s\right)+S{O}_4^{2-}\left(aq\right)+4H^{+}\left(aq\right)+2e^{-}$

During recharging, the cell operates like an electrolytic cell, i.e., now electrical energy is supplied to it from an external source. The electrode reactions are the reverse of those that occur during discharge:
$PbS{O}_4\left(s\right)+2e^{-}\to Pb\left(s\right)+S{O}_4^{2-}\left(aq\right)$
$PbS{O}_4\left(s\right)+2H_{2}O\to Pb{O}_2\left(s\right)+S{O}_4^{2-}\left(aq\right)+4H^{\oplus }\left(aq\right)+2e^{-}2PbS{O}_4\left(s\right)+2H_{2}O\to Pb\left(s\right)+Pb{O}_2\left(s\right)+4H^{\oplus }\left(aq\right)+2S{O}_4^{2-}\left(aq\right)$
Such operation is possible because PbSO₄ formed during discharge is a solid and sticks to the electrodes. It is, therefore, in a position to either receive or give up electrons during electrolysis.