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Question: Write the name of the cell which is generally used in hearing aids. Write the reactions taking place...

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.

Explanation

Solution

In an electrochemical cell, a chemical reaction generates electricity. Oxidation occurs at anode and reduction occurs at cathode.Oxidation is the process in which a substance loses electrons and gains its oxidation state. Reduction is the process in which a substance gains electrons and loses its oxidation state.

Complete answer:
Mercury cell is used in hearing aids.
Write the reaction taking place at the anode of the mercury cell.
Zn(Hg) + 2 OH− → ZnO(s) + H2O + 2e−{\text{Zn}}\left( {{\text{Hg}}} \right){\text{ + 2 O}}{{\text{H}}^ - }{\text{ }} \to {\text{ ZnO}}\left( {\text{s}} \right){\text{ + }}{{\text{H}}_2}{\text{O + 2}}{{\text{e}}^ - }
In the above half-cell reaction, zinc metal is oxidized to zinc oxide. Loss of electrons is oxidation. Gain of oxygen is oxidation. Oxidation half reaction occurs at anode.
The oxidation number of zinc increases from 0 to +2. Increase in the oxidation number is oxidation.
Write the reaction taking place at the cathode of the mercury cell.
HgO(s) + H2O + 2e− → Hg(l) + 2 OH−{\text{HgO}}\left( {\text{s}} \right){\text{ + }}{{\text{H}}_2}{\text{O + 2}}{{\text{e}}^ - }{\text{ }} \to {\text{ Hg}}\left( {\text{l}} \right){\text{ + 2 O}}{{\text{H}}^ - }
In the above half-cell reaction, mercuric oxide is reduced to mercury metal. Gain of electrons is reduction. Loss of oxygen is reduction. Reduction half reaction occurs at cathode. The oxidation number of mercury decreases from -2 to 0. Decrease in the oxidation number is reduction.
Write the overall cell reaction
Zn(Hg) + HgO(s) → ZnO(s) + Hg(l){\text{Zn}}\left( {{\text{Hg}}} \right){\text{ + HgO}}\left( {\text{s}} \right){\text{ }} \to {\text{ ZnO}}\left( {\text{s}} \right){\text{ + Hg}}\left( {\text{l}} \right)
In the overall cell reaction, zinc metal is converted into zinc oxide and mercuric oxide is converted to mercury metal. An oxygen atom is transferred from mercuric oxide to zinc metal.

Note:
In the overall cell reaction, zinc displaces mercury from its oxide. It is an example of a single displacement reaction. It is also an example of redox reaction.