Question

Describe about lead storage battery construction and its uses.

Answer 1

Lead storage battery: 

1. Anode – Spongy lead

Cathode – Lead plate bearing PbO₂

Electrolyte – 38% by mass of H₂SO₄ with density 1.2 g/ml

2. Oxidation occurs at the anode 

Pb_(s) → Pb²⁺_(aq) + 2e^- …..(1)

The Pb²⁺ ions combine with SO^2-₄ to form PbSO₄ precipitate

Pb²⁺_(aq) + SO^2-₄ → PbSO_4(s) ……(2) 

3. Reduction occurs at the cathode

PbO_2(s) + 4H⁺_(aq) + 2e^- → + 2H₂O₍₁₎ ……(3) 

The Pb²⁺ ions also combines with SO^2-₄ ions to form sulphuric acid to form PbSO₄ Precipitate 

Pb²⁺(aq) + SO^2- → PbSO …….(4)

4. The overall reaction is, 

(1) + (2) + (3) + (4)

Pb_(s) + pbO_2(s) + 4H⁺_(s) + 2SO^2-_4(s) → 2PbSO_4(s) + 2H₂O₍₁₎

5. The emf of a single cell is about 2V. Usually six such cells are combined in series to produce 12 volts. 

6. The emf of the cell depends on the concentration of H₂SO₄ . As the cell reaction uses SO₄^2- ions, the concentration H₂SO₄ decreases. When the cell potential falls to about 1.8V, the cell has to be recharged.

7. Recharge of the cell – During recharge process, the role of anode and cathode is reversed and H₂SO₄ is regenerated. Oxidation occurs at cathode (now anode)

The above reaction is exactly the reverse of redox reaction which takes place while discharging.

8. Uses: 

Lead storage battery is used in automobiles, trains, inverters.