Question

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

• A. Pb is oxidised to $\text{PbSO}_{4}$
• B. $\text{PbSO}_{4}$ is oxidised to $\text{PbO}_{2}$
• C. $\text{PbSO}_{4}$ is reduced to Pb
• D. $\text{PbO}_{2}$ is reduced to $\text{PbSO}_{4}$

Hint:

Recharging a battery is literally running the discharge reactions perfectly backwards! Just remember: Discharge turns everything into $\text{PbSO}_4$. Recharge turns it all back into $\text{Pb}$ and $\text{PbO}_2$. Oxidation always happens at the Anode!

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
During recharging, the lead accumulator acts as an electrolytic cell. The reactions that occurred during discharge are reversed.

Step 2: Formula Application:
Positive electrode during discharge: $PbO_2$ is reduced to $PbSO_4$. Positive electrode during recharge: The reverse happens.

Step 3: Explanation:
At the positive electrode (anode during recharge), lead sulfate ($PbSO_4$) is oxidized back to lead dioxide ($PbO_2$). Reaction: $PbSO_4(s) + 2H_2O(l) \to PbO_2(s) + SO_4^{2-}(aq) + 4H^+(aq) + 2e^-$.

Step 4: Final Answer:
$PbSO_4$ is oxidised to $PbO_2$.