CBSE Class 12 · 2011 · Delhi Compartment · Redox Reactions and ElectrochemistryShort Answer

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Mention the reactions occurring at (i) anode, (ii) cathode, during the working of a mercury cell. Why does the voltage of a mercury cell remain constant during its operation?

Solution

Mercury cell:
Anode (zinc amalgam):

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

Cathode (HgO paste):

HgO (s) + H_{2} O + 2 e^{-} ⟶ Hg (l) + 2O H^{-}

Overall:

Zn (Hg) + HgO (s) ⟶ ZnO (s) + Hg (l)

The overall reaction involves only solids and liquids — no electrolyte ion whose concentration changes — so the cell potential remains constant throughout its life.

CBSE Class 12 Board · 2011 · Delhi Compartment · Subjective

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