Question

What happens when the lead storage battery is discharged?
A.$\text{S}{{\text{O}}_{2}}$is discharged
B.Lead sulfate is consumed
C.Lead is formed
D.${{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}$is consumed

Answer 1

Hint:Lead storage batteries are used to store charge and deliver current. The anode is made up of lead and cathode is made up of lead dioxide with sulfuric acid as an electrolyte. While discharging of current the lead at the anode gets oxidized and the consumption of sulfuric acid takes place.

Complete answer:
The lead present at the anode i.e. positive electrode gets oxidized when battery starts discharging.
The reaction is given as- $\text{Pb}\to \text{P}{{\text{b}}^{2+}}+\text{2}{{\text{e}}^{-}}$
The negative ions present in ${{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}$ (sulfuric acid) i.e. $\text{S}{{\text{O}}_{4}}^{2-}$ions start drifting towards positive plate i.e. anode. The following reaction at anode is- $\text{Pb}+{{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}\to \text{PbS}{{\text{O}}_{4}}+\text{2}{{\text{e}}^{-}}$ . So while discharging sulfuric acid which is present as an electrolyte is getting consumed. The lead dioxide present at cathode is reduced- $\text{2}{{\text{e}}^{-}}+\text{Pb}{{\text{O}}_{2}}+4{{\text{H}}^{+}}\to \text{P}{{\text{b}}^{2+}}+2{{\text{H}}_{2}}\text{O}$
The lead ions formed combine with sulfate ions to form lead sulfate. So, water and lead sulfate are being formed and acid is being consumed while discharging the lead battery.

So, the correct choice is (D).

Additional Information:
Lead storage battery normally consists of six voltaic cells in series. Each anode is made of spongy lead and cathode of lead dioxide. Sulfuric acid by $38%$ mass is used as an electrolyte. Acid consumption takes place during discharging and if density of solution falls below $1\cdot 2$ gram per cubic cm then recharging of battery should be done. It is a secondary battery as it can be recharged.

Note:
In recharging of lead storage batteries the reversal of reactions will take place. While recharging, the lead sulfate present at anode is converted to lead and lead sulfate present at cathode is converted to lead dioxide. But these batteries cannot be charged indefinitely as the electrodes lose lead sulfate. The dependence on restricted lead amount is one of the disadvantages of lead storage batteries.