Question

Ammonia is dried over?
(A) Quick Lime
(B) Slaked Lime
(C) Phosphorous Pentoxide
(D) Conc. ${{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}$

Answer 1

Ammonia is a compound of nitrogen and hydrogen and due to the presence of the lone pair of atoms on the nitrogen atom, it is basic in nature. Hence, it reacts with acidic compounds to form salt and water.

Complete step by step solution
Ammonia is prepared in the laboratory by gently heating ammonium chloride or sal ammonia with slaked lime or calcium hydroxide. Though it can also be prepared by heating any ammonium salt with sodium chloride also. The characteristic smell of ammonia is the test for reaction taking place. Being lighter than air, it is collected by the downward displacement of air. Being highly soluble is water, ammonia is not collected over water.
To dry the ammonia gas, it is collected over quick lime or calcium oxide. Due to its basic nature, it cannot be dried over phosphorus Pentoxide or conc. ${{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}$ as it will react with them forming either ammonium sulphate or ammonium phosphate and water.
Calcium chloride cannot be used to dry the gas as it ammoniates with the later. The reactions that take place can be represented as follows:
$\text{N}{{\text{H}}_{\text{4}}}\text{Cl + Ca}{{\left( \text{OH} \right)}_{\text{2}}}\to \text{CaC}{{\text{l}}_{\text{2}}}\text{ + N}{{\text{H}}_{\text{4}}}\text{OH}$ (Ammonia preparation)
$\text{2N}{{\text{H}}_{\text{3}}}\text{ + }{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\to {{\left( \text{N}{{\text{H}}_{\text{4}}} \right)}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}$ (Reaction of ammonia with sulphuric acid)
$\text{4N}{{\text{H}}_{\text{3}}}\text{ + }{{\text{P}}_{\text{2}}}{{\text{O}}_{5}}+3{{\text{H}}_{\text{2}}}\text{O}\to {{\left( \text{N}{{\text{H}}_{\text{4}}} \right)}_{3}}\text{P}{{\text{O}}_{\text{4}}}$ (Reaction of ammonia with phosphorus pentoxide)
Hence, the correct answer is option A, Quick lime or calcium oxide.

Note
The industrial process for the preparation of ammonia is called the Haber Bosch’s Process in which nitrogen is heated along with hydrogen at an optimum temperature and pressure in the presence of iron catalyst and molybdenum promoter.