Explain the functions of lead accumulator.

A secondary cell after use can be recharged by passing current through it in the opposite direction so that it can be used again. A good secondary cell can undergo a large number of discharging and charging cycles. The most important secondary cell is the lead storage battery commonly used in automobiles and invertors. It consists of a lead anode and a grid of lead packed with lead dioxide (PbO₂) as cathode. A 38% solution of sulphuric acid is used as an electrolyte.

The cell reactions when the battery is in use are given below:

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

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

Overall cell reaction consisting of cathode and anode reactions is

 Pb(s) + PbO₂ (s) + 2H₂SO₄ (aq) → 2PbSO₄ (s) + 2H₂O(l) On charging the battery the reaction is reversed and PbSO₄ (s) on anode and cathode is converted into Pb and PbO₂ , respectively