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Electrochemistry

Question
CBSEENCH12005957

What is a mercury cell? Give the electrode reactions?

Solution
A mercury battery (also called mercuric oxide battery, or mercury cell) is a non-rechargeable electrochemical battery, a primary cell. Mercurybatteries use a reaction between mercuric oxide and zinc electrodes in an alkaline electrolyte.

Mercury cell is a new type of dry cell. It consists of
Anode:   Zinc-mercury.
Cathode: Paste of HgO and carbon
Electrolyte: Paste of ZnO in KOH.

The reactions are:
Anode:
Zn (amalgam) + 2OH-ZnO(s)+H2O + 2e-
 
At cathode:
HgO+H2O + 2e-  Hg(l)+2OH-
           
Overall reaction:
Zn(amalgam)+HgO(s)ZnO(s)+Hg(l)