Question

A dry cell consists of a moist paste of $ \text{NH}_4\text{Cl} $ and $ \text{ZnCl}_2 $ contained in a Zn casing which encloses a carbon rod surrounded by black $ \text{MnO}_2 $ paste. What is the role of $ \text{ZnCl}_2 $ in it?

• A. It prevents pressure being developed in the cell due to NH}_3\text{ gas formation.}
• B. It serves as cathode thus permitting Carbon rod to act as anode.
• C. It acts as the anode while Carbon rod acts as the cathode.
• D. It keeps the contents dry and prevents leakage of electrolyte.

Hint:

In dry cells, additives like ZnCl\(_2\) are essential for controlling the formation of gases that could compromise the cell's integrity and performance.

Answer 1

The Correct Option is A

In a dry cell, the ZnCl\(_2\) paste plays a crucial role in preventing excessive buildup of pressure inside the cell, which could occur due to the formation of NH\(_3\) gas during the electrochemical reactions. The NH\(_3\) gas formation could result from the reaction of Zn with NH\(_4\)Cl, causing an increase in pressure. The ZnCl\(_2\) paste, by preventing the formation of NH\(_3\) gas, ensures that the cell remains stable and pressure-free. This allows the cell to function efficiently for a longer time. 
Thus, the correct answer is that ZnCl\(_2\) prevents pressure development due to NH\(_3\) gas formation.