What type of battery is Mercury cell? Why is it more advantageous than dry cell? Write overall reaction taking place in Mercury cell.
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Solution and Explanation
A mercury cell is a type of primary cell (non-rechargeable, used once). Its advantage comes from keeping a steady voltage throughout its life.
Step 1:
Type: The mercury cell is a primary battery. It consists of a zinc-mercury amalgam anode and a paste of \(HgO\) with carbon as the cathode, in a moist paste of \(KOH\) and \(ZnO\) electrolyte.
Step 2:
Advantage: In the mercury cell the overall reaction does not involve any ion whose concentration changes during the cell's life, so the cell potential stays constant (about 1.35 V) throughout. In a dry cell the voltage falls steadily as it is used. This constant voltage makes the mercury cell more advantageous.
Step 3:
Overall reaction: \(Zn(Hg) + HgO(s) \rightarrow ZnO(s) + Hg(l)\).
Answer: Mercury cell is a primary cell. It is more advantageous than a dry cell because it gives a constant voltage (no ions are consumed in the net reaction). Overall reaction: \(Zn(Hg) + HgO(s) \rightarrow ZnO(s) + Hg(l)\).
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