Question

Which of the given statements for mercury cell are incorrect ?

(i) Mercury cell is suitable for low current devices like hearing aids, watches, etc.
(ii) It consists of zinc-mercury amalgam as anode and a paste of $HgO$ and carbon as the cathode.
(iii) The electrolyte is a paste of $Zn(OH)_2$ and $KO_2$.
(iv) The electrode reactions for the cell are
At anode : $Zn\left(Hg\right)+H_{2}O \to ZnO_{\left(s\right)}+2OH^{-}+2e^{-}$
At cathode : $HgO+H_{2}O+2e^{-} \to Hg_{\left(l\right)}+2OH^{-}$

• A. (ii) and (iii) only
• B. (i) and (ii) only
• C. (i), (iii) and (iv) only
• D. (iii) and (iv) only

Answer 1

Answer: (D)

The electrolyte in a mercury cell is a paste of $KOH$ and $ZnO$. The electrode reactions for the cell are
At anode : $Zn\left(Hg\right)+2OH^{-} \rightarrow ZnO_{\left(s\right)}+H_{2}O+2e^{-}$
At cathode : $HgO+H_{2}O+2e^{-} \rightarrow Hg_{\left(l\right)}+2OH^{-}$