Question

A lead storage battery is the most important type of secondary cell having a lead anode a grid of lead packed with PbO₂ as a cathode. A 38% solution of sulphuric acid is used as electrolyte. (Density 1.294gmL⁻¹) The battery holds 3.5L of the acid. During the discharge of the battery, the density of H₂SO₄ falls to 1.139gmL⁻¹.

Write the reaction taking place at the cathode when the battery is in use.

Answer 1

During battery discharge, the cathode reaction involves the reduction of lead dioxide to lead sulfate and the production of water, with a concurrent decrease in the density of the sulfuric acid electrolyte. Cathode (reduction): PbO₂ (s) + HSO₄¯ (aq) + 3H⁺ (aq) + 2e¯ → PbSO₄ (s) + 2H₂O (l)

Step-by-step explanation:

The reaction taking place at the cathode of a lead storage battery during discharge can be represented as follows:

PbO₂(s) + HSO₄¯(aq) + 3H⁺(aq) + 2e⁻ → PbSO₄(s) + 2H₂O(l)

This reaction involves the reduction of lead dioxide (PbO₂) into lead sulfate (PbSO₄) and the formation of water.

During the operation of the battery, sulfuric acid acts as the electrolyte, and its concentration decreases as it is consumed in the electrode reactions, thus reducing the density of the solution.