Question

To dry ammonia $(N{H}_3)$ gas the drying agent used is:
(A) Conc. $H_{2}S{O}_4$
(B) $P_2{O}_5$
(C) soda lime
(D) anhydrous $CaC{l}_2$

Answer 1

Hint: Ammonia $(N{H}_3)$ gas is highly soluble in water and needs to be dried (or water should be removed) for its use in industry and commerce. Ammonia is basic in nature. Hence, it can be dried only by a basic compound.

Complete step by step answer:
Drying agents like sulphuric acid and hydrochloric acid cannot be used to dry ammonia as they react with it very quickly due to the basic nature of ammonia.
Ammonia and phosphorus pentoxide react with each other to form ammonium phosphates.
Calcium chloride is highly hygroscopic in nature and absorbs almost $98\mathrm{\%}$ of water but it reacts exothermically with ammonia to form calcium chloride complexes.
Ammonia can be easily dried by passing over fresh quicklime or soda lime (granules of calcium oxide and sodium hydroxide) because it is basic in nature and doesn’t react with ammonia.
So, the answer is option ‘C’.
Additional information:
 Ammonia is a very commercially important chemical. It is the major source of nitrogen required to synthesize nitrogen containing compounds. It is produced by Haber’s process by extracting nitrogen from air and hydrogen from natural gas. It is very reactive and handled very carefully. It is used in industry to produce nitrogen containing fertilizers like urea. It is used as a refrigerant gas, to clean water supplies and in the manufacture of chemicals like plastics, dyes, explosives, textiles etc.

Note:
Ammonia is a basic gas, easily dissolves in water and reacts with compounds. Calcium chloride, concentrated acids and soda lime, all are dehydrating agents which absorb moisture from substances and are used for drying purposes.