Question

Write the chemical equation to prepare ammonia gas in the laboratory by using an alkali.
State why concentrated sulphuric acid is not used for drying ammonia gas.
Why is ammonia gas not collected over water?

Answer 1

We must know the physical and chemical properties of ammonia and sulphuric acid. Ammonia is a colourless gas with a pungent smell in which one nitrogen atom is connected with three hydrogen atoms with trigonal pyramidal structure.

Complete step by step answer:

1. The chemical equation for preparing ammonia gas in the laboratory by using an alkali is:
$2N{H_4}Cl + Ca{\text{ }}{\left( {OH} \right)_2} \to CaC{l_2} + 2{H_2}O + 2N{H_3}$
​Here, calcium Hydroxide $\left[ {Ca{{\left( {OH} \right)}_2}} \right]$ is an alkali.
2. As the ammonia is basic in nature, it always reacts with concentrated sulphuric acid and also forms ammonium sulphate:
$2N{H_3} + HS{O_4} \to \left( {N{H_4}} \right){\text{ }}2S{O_4}$
The majority of sulphuric acid is used for the preparation of fertilizers for commercial uses. Therefore, sulphuric acid reacts with ammonium hydroxide solution or ammonia to prepare ammonium sulphate$\left( {N{H_4}} \right)2S{O_4}$.
Sulfuric acid is also used in various productions of different paints and detergents. Sulfur is rarely found in its pure form in the ground state. The impurity is produced when fossil fuels are fully burned and it leads to an acid rain around.
​3. Ammonia has an ability to form a hydrogen bond. When there are hydrogen bonds between water molecules which get broken, they can be replaced by equivalent bonds between water and ammonia molecules. This is why ammonia gas does not get collected over water because it gets soluble in it. The solubility of ammonia is mainly due to the hydrogen bonding and not due to the particular reaction.

Note:
We must know that ammonia is colourless gas and has a distinct odour. When we can use ammonia as a gas in refrigerants and air-conditioners, it can absorb some amounts of heat from its surroundings. Anhydrous ammonia gas is significantly lighter than air. However, because of the enormous affinity of ammonia to water, it reacts immediately with the humidity in the air and may remain close to the ground.