Question
The construction and working of the calomel electrode.
✓
Answer
(1) Since standard hydrogen electrode ( SHE ) is not convenient for experimental use, a secondary reference electrode like calomel electrode is used.
(2) Construction : It consists of a glass vessel with side arm B for dipping in a desired solution of another electrode like, $ZnSO _{4( aq )}$ for an electric contact. The vessel is filled with mercury, a paste of Hg and $Hg _2 Cl _2$ (calomel) and saturated KCl solution.
(3) The potential developed depends upon the concentration of $Cl ^{-}$or KCl solution. When saturated KCl solution is used, its reduction potential is $0.242\ V$ .
(4) Consider following cell:
$Zn _{( s )}\left| ZnSO _{4( aq )}\right|\left| KCl _{( aq )}\right| Hg _2 Cl _{2(s)} \mid Hg$
$OR Zn n _{( s )}\left| ZnSO _{4( aq )}\right| \mid$ Calomel electrode
Reduction reaction for calomel electrode:
$Hg_2 Cl_{2(s)}+2 e^{-} \rightarrow 2 Hg_{(l)}+2 Cl_{(aq)}^{-}$
Hence potential of calomel electrode depends on the concentration of $Cl ^{-}$or KCl solution.
(2) Construction : It consists of a glass vessel with side arm B for dipping in a desired solution of another electrode like, $ZnSO _{4( aq )}$ for an electric contact. The vessel is filled with mercury, a paste of Hg and $Hg _2 Cl _2$ (calomel) and saturated KCl solution.
(3) The potential developed depends upon the concentration of $Cl ^{-}$or KCl solution. When saturated KCl solution is used, its reduction potential is $0.242\ V$ .
(4) Consider following cell:
$Zn _{( s )}\left| ZnSO _{4( aq )}\right|\left| KCl _{( aq )}\right| Hg _2 Cl _{2(s)} \mid Hg$
$OR Zn n _{( s )}\left| ZnSO _{4( aq )}\right| \mid$ Calomel electrode
Reduction reaction for calomel electrode:
$Hg_2 Cl_{2(s)}+2 e^{-} \rightarrow 2 Hg_{(l)}+2 Cl_{(aq)}^{-}$
Hence potential of calomel electrode depends on the concentration of $Cl ^{-}$or KCl solution.
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