Question

Write anode, cathode and overall reaction involved in dry cell.

Hint:

In a dry cell, zinc acts as the anode and gets oxidized, while manganese dioxide acts as the depolarizer and undergoes reduction.

Answer 1

Concept: A dry cell is a primary cell that converts chemical energy directly into electrical energy. It is widely used in flashlights, radios, clocks and portable electronic devices. The dry cell consists of:

• Zinc container acting as anode.

• Carbon rod surrounded by \(MnO_2\) acting as cathode.

• Moist paste of \(NH_4Cl\) and \(ZnCl_2\) as electrolyte.
The cell generates electricity through oxidation-reduction reactions.

Step 1: Anode reaction Oxidation occurs at the anode. The zinc container loses electrons. \[ Zn(s)\rightarrow Zn^{2+}+2e^- \] The zinc ions combine with chloride ions present in the electrolyte. \[ Zn+2NH_4Cl \rightarrow ZnCl_2+2NH_3+2H^++2e^- \]

Step 2: Cathode reaction Reduction occurs at the cathode. Manganese dioxide is reduced in the presence of ammonium ions. \[ 2MnO_2+2NH_4^++2e^- \rightarrow Mn_2O_3+2NH_3+H_2O \]

Step 3: Overall cell reaction Adding the anodic and cathodic reactions, \[ Zn+2MnO_2+2NH_4Cl \rightarrow ZnCl_2+Mn_2O_3+2NH_3+H_2O \]

Final Answer \[ \boxed{\text{Anode : }Zn \rightarrow Zn^{2+}+2e^-} \] \[ \boxed{ 2MnO_2+2NH_4^++2e^- \rightarrow Mn_2O_3+2NH_3+H_2O } \] \[ \boxed{ Zn+2MnO_2+2NH_4Cl \rightarrow ZnCl_2+Mn_2O_3+2NH_3+H_2O } \]