Why is concentrated sulfuric acid not used to dry ammonia?

• A. Because it will react with the base ammonia, which is a neutralisation reaction.
• B. It will absorb ammonia gas without reacting.
• C. It will form a stable complex with water.
• D. It will evaporate too quickly

Answer: (A)

This tests how drying agents interact with the substance being dried and the chemical nature of ammonia. Ammonia is a base, while concentrated sulfuric acid is a strong acid. When a base meets a strong acid, they neutralize to form a salt. If ammonia gas were passed over concentrated sulfuric acid, they would react to form ammonium sulfate, effectively consuming the ammonia and converting the drying agent into a salt instead of simply removing water. That means the gas wouldn’t be dried properly because the ammonia would be trapped in a solid salt and the drying agent would be used up in the reaction. The idea that the acid would just absorb ammonia without reacting isn’t correct because a strong acid will react with a base. The notion of forming a stable complex with water or evaporating too quickly doesn’t capture the essential issue here—the chemical reaction between ammonia and the acid prevents effective drying.