Question

Which of the following is true for mercury cell?

• A. Products of the electrode reactions are separated by thin membrane
• B. Paste of $HgO$ and carbon will act as anode
• C. Zinc – mercury amalgam will act as cathode
• D. All of the above.

Answer 1

The correct option is A Products of the electrode reactions are separated by thin membrane

In mercury cell,
Zinc – mercury amalgam will act as anode
Paste of $HgO$ and carbon will act as cathode
Paste of $KOH$ and $ZnO$ will be the electrolyte
In mercury cell, there will be a thin polymeric membrane which prevents the mixing of products formed at the electrodes. This membrane is called separator.
Reaction at electrodes:

At anode :
$Zn\left(Hg\right)+2O{H}^{-}\to ZnO\left(s\right)+H_{2}O+2e^{-}$

At cathode:
$HgO+H_{2}O+2e^{-}\to Hg\left(l\right)+2O{H}^{-}$

Overall cell reaction
$Zn\left(Hg\right)+HgO\left(s\right)\to ZnO\left(s\right)+Hg\left(l\right)$