Question

Draw a neat and labelled diagram of a lead accumulator cell. Write the overall reactions taking place at cathode and anode during discharging of the cell.

Hint:

A useful mnemonic for electrode reactions is "An Ox" (Anode is Oxidation) and "Red Cat" (Reduction at Cathode). Note that during the discharge of a lead-acid battery, both electrodes become coated with lead(II) sulfate, and the concentration of the sulfuric acid electrolyte decreases.

Answer 1

Lead Accumulator Cell
A lead accumulator is a secondary (rechargeable) cell. It consists of a lead anode and a grid of lead packed with lead dioxide (PbO\(_2\)) as the cathode. The electrolyte is an aqueous solution of sulphuric acid (about 38% H\(_2\)SO\(_4\)).
Reactions during Discharging:


Anode (Oxidation): The lead anode is oxidized to lead(II) sulfate. \[ \text{Pb(s)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{PbSO}_4\text{(s)} + 2e^- \]
Cathode (Reduction): The lead dioxide cathode is reduced to lead(II) sulfate. \[ \text{PbO}_2\text{(s)} + \text{SO}_4^{2-}\text{(aq)} + 4\text{H}^+\text{(aq)} + 2e^- \rightarrow \text{PbSO}_4\text{(s)} + 2\text{H}_2\text{O(l)} \]
Overall Cell Reaction:
Adding the anode and cathode half-reactions gives the overall reaction: \[ \text{Pb(s)} + \text{PbO}_2\text{(s)} + 2\text{H}_2\text{SO}_4\text{(aq)} \rightarrow 2\text{PbSO}_4\text{(s)} + 2\text{H}_2\text{O(l)} \]