In a mercury cell, zinc-mercury amalgam is used as an anode and carbon is used as a cathode. A paste of _______ is used as an electrolyte.

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RRB ALP Electronics Mechanic 23 Jan 2019 Official Paper (Shift 3)
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  1. HgO
  2. LiFe
  3. H2O
  4. H2SO4

Answer (Detailed Solution Below)

Option 1 : HgO
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  • In a mercury cell, the electrolyte used is typically a paste of potassium hydroxide (KOH) and mercury(II) oxide (HgO).
  • The paste serves as a source of hydroxide ions (OH-) that are needed to complete the electrochemical reaction occurring in the cell.
  • The reaction at the anode involves the oxidation of the zinc in the amalgam to form zinc ions (Zn2+) and electrons (e-).

 

While at the cathode, the reduction of the mercury(II) oxide and the production of liquid mercury takes place.

Overall, the reaction can be represented as:

Zn(Hg) + HgO(s) + 2 KOH(aq) → ZnO(s) + Hg(l) + 2 K[Hg] + H2O(l)

where [Hg] represents a complex of mercury and potassium.

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