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

Step 1: Anode reaction (oxidation of zinc).
The zinc container is oxidized in the $NH_4Cl$ electrolyte paste: \[ Zn + 2NH_4Cl \rightarrow ZnCl_2 + 2NH_3 + 2H^+ + 2e^- \]
Step 2: Cathode reaction (reduction of $MnO_2$).
$MnO_2$ surrounding the carbon rod accepts electrons and $Mn$ is reduced from $+4$ to $+3$: \[ 2MnO_2 + 2NH_4^+ + 2e^- \rightarrow Mn_2O_3 + 2NH_3 + H_2O \]
Step 3: Overall cell reaction.
Adding both half-reactions:
\[ \boxed{Zn + 2MnO_2 + 2NH_4Cl \rightarrow ZnCl_2 + Mn_2O_3 + 2NH_3 + H_2O} \]