What are the physical properties of ammonia?

What are the physical properties of ammonia?

1. Ammonia is a covalent compound with the following physical properties:
   
2. Ammonia is very soluble in water, but it ionises partially in water to form a weak alkali. A 0.1 mol dm^-3 ammonia solution has a pH of about 10.
   
3. Ammonia being alkaline can undergo neutralisation with acids to form ammonium salts.
   Ammonia + Acid → Ammonium salt
   Examples:
   (a) Ammonia neutralises sulphuric acid to form ammonium sulphate.
   2NH₃(aq) + H₂SO₄(aq) → (NH₄)2SO₄(aq)
   (b) Ammonia gas reacts with hydrogen chloride gas to form dense white fumes of ammonium chloride. This is used as a test for detecting ammonia gas.
   NH₃(g) + HCl(g) → NH₄Cl(s)
4. Ammonia solution can react with solutions of some metal ions (except Na⁺ ion, K⁺ ion and Ca²⁺ ion) to produce precipitate of metal hydroxide.
   Mⁿ⁺(aq) + nOH^–(aq) → M(OH)_n(s)
   Examples:
   (a) Ammonia reacts with copper ions to produce a blue precipitate, copper(II) hydroxide.
   
   Copper(II) hydroxide dissolves in excess ammonia solution to form a dark blue solution.
   (b) Ammonia reacts with zinc ions to produce a white precipitate, zinc hydroxide.
   
   Zinc hydroxide dissolves in excess ammonia solution to form a colourless solution.
   (c) Ammonia reacts with iron(III) ions to produce a brown precipitate, iron(III) hydroxide.
   
   (d) Ammonia reacts with magnesium ions to produce a white precipitate, magnesium hydroxide.
   
5. Ammonia does not burn in air, but in the presence of platinum catalyst in oxygen, ammonia can burn to produce nitrogen dioxide.
   4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(l)

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Laboratory preparation of ammonia gas experiment

Aim: To investigate the properties of ammonia.
Materials: 0.1 mol dm^-3 ammonia solution, 0.1 mol dm^-3 sodium hydroxide solution, ammonium chloride, calcium hydroxide, concentrated hydrochloric acid, soda-lime, distilled water, red litmus paper, pH paper.
Apparatus: Test tubes, beaker, U-tube, Bunsen burner, glass rod, delivery tube, stoppers.
Procedure:

Safety Measures

• Do not inhale ammonia gas.
• Concentrated hydrochloric acid is corrosive.
• Carry out this activity in a fume chamber.

A. Preparation of ammonia gas

1. One spatula of ammonium chloride is mixed with one spatula of calcium hydroxide.
2. The apparatus as shown in Figure is set up.
3. The mixture is heated strongly.
4. The ammonia gas produced is collected in a few test tubes. The test tubes containing ammonia gas must be closed with stoppers.

B. Alkalinity of ammonia

1. 5 cm³ of 0.1 mol dm^-3 ammonia solution and 5 cm³ of 0.1 mol dm^-3 sodium hydroxide solution are poured into two separate test tubes.
2. A piece of pH paper is dipped into the solution in each test tube.
3. The pH values of both solutions are recorded.

C. Colour, physical state, smell and solubility of ammonia

1. The colour and physical state of ammonia are observed.
2. The stopper of a test tube containing ammonia gas is removed and the smell of the gas is identified.
3. A test tube containing ammonia gas is inverted into a beaker of water.
4. All observations are recorded.

D. Density of ammonia

1. A test tube containing ammonia gas is held upright and another test tube containing ammonia gas is held upside down.
2. The stoppers of the two test tubes are removed.
3. After 20 seconds, a piece of moist red litmus paper is put at the mouth of each test tube as shown in Figure.
4. The colour of the red litmus paper is recorded.

E. Chemical property of ammonia

1. One end of a glass rod is dipped into concentrated hydrochloric acid.
2. The glass rod is then put on top of a test tube of ammonia gas.
3. Any change taking place is observed.

Observations:

Discussion:

1. Ammonia is a weak alkali and has a pH of 10.
2. Ammonia is a colourless gas with a pungent smell.
3. Ammonia is very soluble in water, ionises partially in water to form ammonium ions and hydroxide ions.
   
4. Ammonia is slightly less dense than air.
5. Ammonia reacts with hydrogen chloride gas to form ammonium chloride.
   NH₃(g) + HCl(g) → NH₄Cl(S)

Conclusion:
Ammonia is an alkaline, colourless gas with a pungent smell. It is very soluble in water and is less dense than air. It reacts with hydrogen chloride gas to form dense white fumes of ammonium chloride.