Write the cell reaction of a lead storage battery when it is discharged. How does the density of the electrolyte change when the battery is discharged?

Question

Philoid · Accepted Answer

The cell reaction of lead storage battery when it is discharged is give below:

At anode: Pb(s) + SO₄^2–(aq) → PbSO₄ (s) + 2e^–

At cathode: PbO₂(s)+ SO₄^2–(aq)+4H⁺(aq) +2e^–→PbSO₄(s)+2H₂O (l)

Overall reaction:

Pb(s)+PbO₂(s)+2H₂SO₄(aq)→ 2PbSO₄(s) + 2H₂O(l)

The density is high when the concentration of H₂SO₄ is high, but during discharge this sulphuric acid gets consumed and becomes diluted with water. So, density decreases as the product water form dilute the H₂SO₄ concentration during the discharge of the battery.