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

Question

Read the given passage and answer the questions .

A Lead storage battery is the most important type of secondary cell having a lead anode and a grid of lead packed with PbO₂ as cathode. A 38% solution of sulphuric acid is used as electrolyte. (Density =1.294 g mL^-1) The battery holds 3.5 L of the acid. During the discharge of the battery, the density of H₂SO₄ falls to 1.139 g mL^-1 . (20% H₂SO₄ by mass)

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

(2)  How much electricity in terms of Faraday is required to carry out the reduction of one mole of PbO₂?

(3)  What is the molarity of sulphuric acid before discharge? 

(4)  Lead storage battery is considered a secondary cell. Why? 

(5)  Write the products of electrolysis when dilute sulphuric acid is electrolysed using Platinum electrodes. 

Answer 1

Reaction taking place at cathode when the battery is in use:

1.  PbO₂ (s) + SO^2-₄ (aq) +  4H⁺ (aq) + 2e^- → pbSO₄(s) + 2H₂O(I)

2.  2 F

3.   Molarity = 38 x 1.294 x 1000/98 x 100 = 5.02 M

4.   It can be recharged after use.

5.   At anode: O₂ (g)

At cathode: H₂ (g)