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Question

What happens when lead storage battery is discharged?

A

SO2 is evolved

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B
Lead sulphate is consumed
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C
Lead is formed
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D

H2SO4 is consumed

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Solution

The correct option is D

H2SO4 is consumed


In lead storage battery, lead grids filled with spongy lead will act as anode and lead grids filled with PbO2 will act as cathode. 38% solution of sulphuric acid will act as the electrolyte for the cell.
When the battery discharge,
At anode: Pb(s)+SO24(aq)PbSO4(s)+2e
Most of the lead sulphate precipitates formed gets sticks to the lead rod. Thus, it is not consumed during discharging.

At cathode: PbO2(s)+SO24(aq)+4H+(aq)+2ePbSO4(s)+2H2O(l)
Here also formed lead sulphate precipitate gets sticks
to cathode rod.

Overall reaction during discharge:
Pb(s)+PbO2(s)+2H2SO4(aq)2PbSO4(s)+2H2O(l)
Ecell=2.05 V

H2SO4 is consumed in the cell reaction during discharge. So, its concentration in the solution decreases and results into decrease in the density of the solution.


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