Question

Which of the following is true for a dry cell? a) It contains boric acid, which is a solid acid. b) The graphite rod does not undergo reduction, even though it is the cathode. c) It can be recharged many times. d) all of the above

Answer 1

A dry cells has b) The graphite rod does not undergo reduction, even though it is the cathode.

Answer 2

Answer: b) The graphite rod does not undergo reduction, even though it is the cathode.

Explanation: Dry cell, is compact form of Leclanche cell. It consists of a cylindrical zinc container which acts as anode. A graphite rod which acts as cathode is placed in the center and is coated with  powdered $MnO_2$ and carbon. The in between space is filled with a paste of $NH_4Cl$ and $ZnCl_2$

At anode: Oxidation

$Zn\rightarrow Zn%{2+}+2e^-$

At cathode: Reduction

$2MnO_2+2NH_4^++2e^-\rightarrow Mn_2O_3+2NH_3+H_2O$

Thus it is $MnO_2$ and not graphite which undergoes reduction.