Question

The following questions are based on the preparation of ammonia gas in the laboratory :
How is ammonia gas collected ?

Answer 1

Hint: The ammonia gas is less dense than air. So, it will rise to the top of the air in the container. Thus, it is collected by upward delivery method. The gas is soluble in water so the container to collect it must be dry.

Complete step by step answer:
The ammonia is a colourless gas. It has pungent odour and is poisonous in nature. It is the key component in the production of many industrial products. In industries, it is often manufactured by Haber’s process at large scale. In the laboratories, it is prepared at small scale by the following reaction. The reaction is as-
It is prepared by gently heating the ammonium chloride and calcium hydroxide as-
$2N{H_4}Cl + Ca{(OH)_2} + Heat \to CaC{l_2} + 2N{H_4}OH \to N{H_3} + 2{H_2}O$

The ammonia is lighter than air. So, if in a container it is present. It will be above the air.
So, it is collected by upward delivery method or the gas syringe method.
In the upward delivery method, the jar containing the gas is connected by a tube to the flask that is giving off gas. As ammonia is less dense than air; so, it will rise to the top of the jar. The air in the gas jar is displaced until it is filled with collected gas.

Note: The ammonia gas is soluble in water. So, during collection of gas, the jar must be dry to avoid solubilisation of gas. All the ammonium salts are also soluble in water. These may react with sodium hydroxide giving ammonia. In solution, the ammonia may form ammonium hydroxide and behave as a weak base.