A) Hg is more inert than Pt
B) more voltage is required to reduce \[{{H}^{+}}\] at Hg than at Pt
C) Na is dissolved in Hg while it does not dissolved in Pt
D) concentration of \[{{H}^{+}}\] ions is larger when Pt electrode is taken
Correct Answer: B
Solution :
Sodium chloride in water dissociates as \[NaCl\rightleftharpoons N{{a}^{+}}+C{{l}^{-}}\] \[{{H}_{2}}O\rightleftharpoons {{H}^{+}}+O{{H}^{-}}\] when electric current is passed through this solution using platinum electrode, \[N{{a}^{+}}\] and \[{{H}^{+}}\] move towards cathode. Whereas \[C{{l}^{-}}\] and \[O{{H}^{-}}\] ions move towards anode. At cathode: \[{{H}^{+}}+{{e}^{-}}\xrightarrow[{}]{{}}H\] \[H+H\xrightarrow[{}]{{}}{{H}_{2}}\] At anode:- \[C{{l}^{-}}-{{e}^{-}}\xrightarrow[{}]{{}}\,Cl\] \[Cl+Cl\xrightarrow[{}]{{}}C{{l}_{2}}\] If mercury is used as cathode, \[{{H}^{+}}\] tons are not discharged at mercury cathode because mercury has a high hydrogen over voltage. \[N{{a}^{+}}\] ions are discharged at cathode in preference of H+ ions yielding sodium, which dissolves in mercury to form sodium amalgam.
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