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 \[NaClN{{a}^{+}}+C{{l}^{-}}\] \[{{H}_{2}}O{{H}^{+}}+O{{H}^{-}}\] 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, \[{{H}^{+}}\] ions 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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