First slide

Batteries

Question

What is cathodic reaction occurring in the commonly used mercury cell ?

Easy

A

$Zn (Hg) + 2 {OH}^{-} ⟶ ZnO (s) + H_{2} O + 2 e^{-}$
B

$HgO + H_{2} O + 2 e^{-} ⟶ Hg (l) + 2 {OH}^{-}$
C

$Zn + 2 {OH}^{-} ⟶ ZnO (s) + H_{2} O + 2 e^{-}$
D

$Zn (Hg) + HgO (s) ⟶ ZnO (s) + Hg (l)$

Solution

$Anode Zn (Hg) + 2 {OH}^{-} (aq) ⟶ ZnO (s) + H_{2} O + 2 e^{-}$
$Cathode HgO (s) + H_{2} O + 2 e^{- -} ⟶ Hg (l) + 2 {OH}^{-}$
The Overall reaction is $Zn (Hg) + HgO (s) ⟶ ZnO (s) + Hg (l)$

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