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CBSE Class 12 Chemistry 2017 Outside Delhi Set 1 Solved Paper

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Question : 9 of 26
Marks: +1, -0
Write the name of the cell which is generally used in hearing aids. Write the reactions taking place at the anode and the cathode of this cell.
Solution:  
Mercury cell is generally used in hearing aids.
At anode: Zn(Hg)+2 OH−→ZnO(s)+H2O+2 e−\mathrm{Zn(Hg)} + 2\,\mathrm{OH}^- \rightarrow \mathrm{ZnO(s)} + \mathrm{H}_2\mathrm{O} + 2\,\mathrm{e}^-
At cathode: HgO(s)+H2O+2 e−→Hg(l)+2 OH−\mathrm{HgO(s)} + \mathrm{H}_2\mathrm{O} + 2\,\mathrm{e}^- \rightarrow \mathrm{Hg(l)} + 2\,\mathrm{OH}^-
Overall reaction: Zn(Hg)+HgO(s)→ZnO(s)+Hg(l)\mathrm{Zn(Hg)} + \mathrm{HgO(s)} \rightarrow \mathrm{ZnO(s)} + \mathrm{Hg(l)}
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