MHT CET202313 May 2023Morning ShiftChemistryElectrochemistryActual
Identify the overall oxidation reaction that occurs in lead storage cell during discharge.
Options
- APb _ ( aq ) ⁺⁺+ SO _ 4( sq ) ⁻⁻ PbSO _ 4( ~s )
- BPbSO _ 4( ~s ) +2 H ₂ O _ (0) PbO _ 2( ~s ) +4 H _ ( aq ) ⁺ + SO _ 4( xq ) ⁻⁻+2 e ⁻
- CPb _ (8) + SO _ 4( aq ) ⁻⁻ PbSO _ 4( ~s ) +2 e ⁻
- DPbSO _ 4( ~s ) +2 e ⁻ Pb _ ( s ) + SO _ 4( mp ) ⁻⁻
Correct answer
C. Pb _ (8) + SO _ 4( aq ) ⁻⁻ PbSO _ 4( ~s ) +2 e ⁻
Step-by-step solution
When the lead storage cell provides current (i.e., during discharge), spongy lead ( Pb ) is oxidised to Pb ²⁺ ions and negative charge accumulates on lead plates. The Pb ²⁺ ions so formed combine with SO ₄²⁻ ions from H ₂ SO ₄ to form insoluble PbSO ₄ . The overall oxidation is the sum of these two processes. aligned & Pb _ ( s ) Pb _ ( (4) ²⁺+2 e ⁻ (oxidation) & Pb _ ( (aq) ²⁺+ SO _ 4( (4) ) ²⁻ PbSO _ 4( ~s ) (precipitation) & Pb _ ( s ) + SO _ 4( (aq) ²⁻ PbSO _ 4( ~s ) +2 e ⁻ aligned (Overall oxidation)