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  4. A button cell used in watches function as following Zn(s) + Ag2O(s) + H2O(l) leftharpoons 2Ag(s) + Zn2+ (aq) + 2OH-(aq) If half cell potentials are Zn2+ (aq) + 2e- arrow Zn(s); E° = -0.76 V Ag2O(s) + H2O(l) + 2e- arrow 2Ag(s) + 2OH-(aq); E° = 0.34 V

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Q. A button cell used in watches function as following
$Zn(s) + Ag_2O(s) + H_2O(l) \rightleftharpoons 2Ag(s) + Zn^{2+} (aq) + 2OH-(aq)$
If half cell potentials are
$Zn^{2+}_{ (aq)} + 2e- \rightarrow Zn(s); E^{\circ} = -0.76\,V$
$Ag_2O_{(s)} + H_2O_{(l)} + 2e- \rightarrow 2Ag_{(s)} + 2OH^{-}_{(aq)};$
$E^{\circ} = 0.34\,V$

NEETNEET 2013Electrochemistry

Solution:

$Zn ^2+( aq )+2 e ^{-} \longrightarrow Zn ( s ) ; E ^{\circ}=-0 \cdot 76 V$
$Ag _2 O ( s )+ H _2 O ( l )+2 e ^{-} \longrightarrow 2 Ag ( s )+2 OH -( aq )$
$E^{\circ}=0.34 V$
$Zn ( s )+ Ag _2 O ( s )+ H _2 O ( l ) \longrightarrow 2 Ag ( s )+ Zn ^{+2}( aq )+2 OH -( aq ) ; E _{\text {cell }}=?$
$E _{\text {cell }}^{\circ}=\left( E _{ R \cdot P }^{\circ}\right)_{\text {cathode }}-\left( E _{ R \cdot P \cdot}^{ o }\right)_{\text {anode }}$
$E _{\text {cell }}^{\circ}=0 \cdot 34-(-0 \cdot 76)=1 \cdot 10 V$
$E _{\text {cell }}= E _{\text {cell }}^{\circ}=1 \cdot 10 V$