Question

How does the density of the electrolyte change when a lead storage battery is discharged?

Answer 1

In lead storage battery sulphuric acid acts as the electrolyte. During the working of the cell PbSO₄ is formed at each electrode and hence sulphuric acid is being used up. As a result concentration of sulphuric acid decreases and density of the solution also decreases. When density falls below 1.2 g mL^-1 the battery needs recharging.