Question

How is an aqueous solution of ammonia prepared? State two advantages of method used.

Answer 1

Preparation of liquid ammonia:
It involves dissolving ammonia gas in water. However, ammonia dissolves in water very rapidly, faster than it can be produced. As a result, if a tube carrying ammonia gas is directly immersed in water, ammonia will dissolve rapidly. This creates a partial vacuum in the tube, leading the water to rise up in the tube by the process of back suction. This water may also enter the flask in which ammonia is being produced. The entry of water into the hot flask will cause it to break. To prevent this, a set up as shown below is used.


A funnel is attached to the end of the delivery tube, and the mouth of the funnel is dipped into the water in the trough. As ammonia dissolves, water is drawn into the funnel by partial vacuum and the mouth of the funnel loses contact with the water in the trough. Gravity and stream of ammonia in the gas line then push the water back again, preventing it from entering the gas delivery line. This allows ammonia to dissolve in the water without back suction. This method has the following advantages:

1. Back suction of water into the gas line and ammonia producing flask is prevented.
2. A large surface area is available for the dissolution of ammonia gas.