Question

Which of the following does not occur during the process of charging a lead storage battery

• A. Increase in concentration of electrolyte
• B. Increase in relative density of electrolyte
• C. Conversion of $PbS{O}_4$ to $Pb$ and $PbO$
• D. Decrease in relative density of electrolyte

Answer 1

The correct option is D Decrease in relative density of electrolyte

Lead Storage Battery:-
When the battery discharge,
At anode: $Pb\left(s\right)+S{O}_4^{2-}\left(aq\right)\to PbS{O}_4\left(s\right)+2e^{-}$
Most of the lead sulphate precipitates formed gets sticks to the lead rod. Thus, it is not consumed during discharging.

At cathode: $Pb{O}_2\left(s\right)+S{O}_4^{2-}\left(aq\right)+4H^{+}\left(aq\right)+2e^{-}\to PbS{O}_4\left(s\right)+2H_{2}O\left(l\right)$
Here also formed lead sulphate precipitate gets sticks
to cathode rod.

Overall reaction during discharge:
$Pb\left(s\right)+Pb{O}_2\left(s\right)+2H_{2}S{O}_4\left(aq\right)\to 2PbS{O}_4\left(s\right)+2H_{2}O\left(l\right)$
$E_{cell}=2.05V$
$H_{2}O$ is produced in the cell reaction.
$H_{2}S{O}_4$ is consumed in the cell reaction during discharge. So, its concentration in the solution decreases and results in decrease in the density of the solution.

On charging the lead storage battery, the reactions are reversed
and produce $H_{2}S{O}_4$

At anode: $PbS{O}_4$ gets converted
into $Pb$

At cathode: $PbS{O}_4$ gets converted into $Pb{O}_2$

Cell reaction:
$2PbS{O}_4\left(s\right)+2H_{2}O\left(l\right)\to Pb\left(s\right)+Pb{O}_2\left(s\right)+2H_{2}S{O}_4\left(aq\right)$

$H_{2}S{O}_4$ is produced in the cell reaction during charging. So, its concentration in the solution increases and results in increase in the density of the solution.