Question

In lead storage battery, what happens to the mass of PbO2 on charging and discharging respectively?

Answer 1

In a lead storage battery, on charging and discharging, the mass of PbO₂ increases and decreases respectively.

• The cathode of a lead storage battery is made up of lead oxide, i.e., PbO₂.

• During the discharging of battery, this PbO₂ is converted into lead sulphate, i.e., PbSO₄ according to the following reaction:

PbO₂ + SO₄²⁻ + 4 H⁺ + 2 e⁻ ⇄ PbSO₄ + 2 H₂O

• So the mass of PbO₂ decreases during discharging.

• During the charging of battery, the reverse process happens and PbSO₄ is converted into PbO₂ according to the following reaction:

PbSO₄ + 2 H₂O ⇄ PbO₂ + SO₄²⁻ + 4 H⁺ + 2 e⁻

• So, the mass of PbO₂ increase on charging.