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Electrochemistry — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryElectrochemistry4 Marks
Question
Write the electrode reactions when lead storage cell generates electricity. What are the anode and cathode and the electrode reactions during its recharging?
✓

Answer

Recharging of the cell : When the discharged battery is connected to external electric source and a higher external potential is applied the cell reaction gets reversed generating $H_2SO_4$​​​​​​​.
Reduction at the – ve electrode or cathode :$PbSO _{4( s )}+2 e ^{-} \rightarrow Pb ^{(s)}+ SO _{4( aq )}^{2-}$
Oxidation at the + ve electrode or anode :
$PbSO _4^{( s )}+2 H _{2( (1) } O \rightarrow PbO _2^{( s )}+4 H _{( aq )}^{+}+ SO _{4( aq )}^{2-}+2 e ^{-}$
The net reaction during charging is
$2 PbSO _{4(3)}+2 H _2 O _{( i )} \rightarrow Pb _{( s )}+ PbO _{2( s )}+4 H _{( aq )}^{+}+2 SO _{4( aq )}^{2-}$
$O R$
$2 PbSO _4^{(s)}+2 H _2 O \rightarrow Pb (s)+ PbO _{2^{(s)}}+2 H _2 SO _{4(\text { (aq) }}$
The emf of the accumulator depends only on the concentration of $H_2SO_4$​​​​​​​.

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