COMEDK2024Evening ShiftChemistryElectrochemistryActual
A dry cell consists of a moist paste of NH ₄ Cl and ZnCl ₂ contained in a Zn casing which encloses a Carbon rod surrounded by black MnO ₂ paste. What is the role of ZnCl ₂ in it?
Options
- AIt acts as the anode while Carbon rod acts as the cathode.
- BIt prevents pressure being developed in the cell due to NH ₃ gas formation.
- CIt serves as cathode thus permitting Carbon rod to act as anode.
- DIt keeps the contents dry and prevents leakage of electrolyte.
Correct answer
B. It prevents pressure being developed in the cell due to NH ₃ gas formation.
Step-by-step solution
In a Leclanche dry cell, the zinc casing acts as the anode and the carbon rod acts as the cathode. The electrolyte is a moist paste of NH ₄ Cl and ZnCl ₂ . The chemical reaction at the cathode involves the reduction of MnO ₂ and the production of ammonia gas, NH ₃ . Specifically, NH ₄⁺ ions react to form NH ₃ . The NH ₃ gas produced would otherwise build up pressure inside the cell. ZnCl ₂ reacts with NH ₃ to form a complex salt, [ Zn ( NH ₃)₂ Cl ₂] , which prevents the accumulation of ammonia gas and the resulting