Ammonia Gas Laboratory Preparation, Properties and Uses

Arush Rijal

August 10, 2024

Ammonia (NH₃)

Ammonia is found in both free and combined states in nature. This gas is produced when nitrogenous substances decay in the absence of oxygen. Similarly, in combined form, ammonia gas is found in ammonium chloride and ammonium sulfate. Lavoisier prepared this gas by heating the mixture of ammonium chloride and calcium hydroxide.

Facts about Ammonia Gas

Symbol	Molecular Weight
NH₃	17

symbol and molecular weight of ammonia gas

The molecular weight of ammonia is 17. The molecular weight of oxygen is 32, whereas the molecular weight of nitrogen is 28 and that of carbon dioxide is 44, so this gas is lighter than the air.

Laboratory Preparation of Ammonia Gas

In the laboratory, ammonia gas is prepared by heating the mixture of ammonium chloride (NH₄Cl) and calcium hydroxide (Ca(OH)₂) in a ratio of 2:1 in a hard glass test tube.

ammonium chloride + calcium hydroxide → calcium chloride + water + ammonia

2NH₄Cl (s) + Ca(OH)₂ (s) → CaCl₂ (s) + 2H₂O (l) + 2NH₃ (g)

Apparatus Required

hard glass test tube, source of heat, gas jar, stand, lime tower, delivery tube, etc.

Chemicals Required

Ammonium Chloride and Calcium Hydroxide

Method/Procedure

Collect the apparatus and chemicals required for the laboratory preparation of ammonia gas.
Mix ammonium chloride and calcium hydroxide in a ratio of 2:1 and put the mixture into a hard glass test tube.
Fix a delivery tube in the mouth of the test tube with a rubber cork to make it airtight as shown in the figure. Arrange the hard glass test tube in a slightly inclined position with the help of a stand. Connect the other end of the delivery tube to the lime tower to obtain pure and dry ammonia gas. We can perform the experiment without the lime tower to get impure ammonia.
Now heat the mixture gently and observe the formation of ammonia gas.
A lime tower filled with Calcium oxide (CaO) is used to obtain the pure and dry ammonia. This gas is quite soluble in water so it is not obtained by the displacement of water. It is collected by the downward displacement of air as it is lighter than the air.

Precautions

The mouth of the hard glass test tube should be slightly inclined downward so that the water vapor produced in this process passes to the lime tower through the delivery tube and prevents the hard glass tube from cracking.
The mouth of the hard glass test tube should be airtight with the help of the cork.
To obtain dry ammonia gas, the should be passed through a lime tower. Since the gas is highly soluble in water, it should not be collected by the displacement of water.

Calcium oxide absorbs moisture from ammonia. So, when ammonia is passed through the lime tower, we get pure and dry ammonia.

Test of Ammonia Gas

The gas is basic so it changes from moist red litmus to blue.
When a glass rod dipped in concentrated hydrochloric acid is brought near the mouth of a gas jar with ammonia, white fumes come out of it.

Properties of Ammonia Gas

Physical Properties

It is a colorless gas with a strong pungent odor like a rotten egg.
It is lighter than the air.
This gas is highly soluble in water.
It is a basic gas so it changes moist red litmus to blue.
Ammonia liquefies at -33 degrees celcius and solidifies at -78 degrees celcius.

Chemical Properties

This gas is soluble in water. It forms ammonium hydroxide when dissolved in water.

NH₃ (g) + H₂O (l) → NH₄OH (aq)

Ammonia reacts with acids to form ammonium salts.

NH₃ (g) + HCl (aq) → NH₄Cl (aq)

2NH₃ (g) + H₂SO₄ (aq) → (NH₄)₂SO₄ (aq)

Ammonium solution (NH4OH) reacts with acid to form salt and water.

2NH₄OH (aq) +H₂SO₄ (aq) → (NH₄)₂SO₄ (aq) + 2H₂0 (l)

NH₄OH (aq) +HCl (aq) → NH₄Cl (aq) +H₂O (l)

Ammonia and carbon dioxide react at a high temperature of 1500 degrees Celsius and at high pressure to form urea.

2NH₃ (g) + CO₂ (g) - pressure+temperature → NH₂-CO-NH₂ (s) + H₂0 (l)

Urea is an important fertilizer.

When ammonia burns in the atmosphere of oxygen, it produces nitrogen gas and water.

4NH₃ (g) + 3O₂ (g) → 6H₂O (l) + 2N₂ (g)

When a mixture of ammonia and oxygen is passed through the platinum gauze at about 800 degrees Celsius, it produces nitric oxide.

4NH₃ (g) + 5O₂ (g) → 6H₂O (l) + 4NO (g)

When ammonia is passed through the molten sodium then it forms sodamide and hydrogen gas.

2NH₃ (g) + 2Na (s) → 2NaNH₂ +H₂ (g)

Uses of Ammonia Gas

Ammonia is used to make fertilizers like ammonium sulfate, ammonium nitrate, urea, ammonium phosphate, etc.
It is used in the manufacture of nitric acid, plastic, etc.
This gas is used to make washing soda.
It is used to make medicines of ammonium salts.
Ammonia is used to make the blueprints of maps.
It is used as a cooling agent in refrigerators.
It is used as a cleansing agent to remove the satins of oil, grease, etc.