ICSE Class 10 Chemistry Chapter 09 Ammonia

Chapter 9: Ammonia

Important Points To Remember

1. Nitrogen was discovered by Daniel Rutherford. The properties of this gas were studied by Lavoisier and Chaptal named the gas Nitrogen.

2. Nitrogen is present in group 15 and in second period in the periodic table.

Electronic configuration: 2, 5

3. Nitrogen forms a diatomic molecule.

N=N with N2- Triple covalent bond

4. Nitrogen occurs in free state as well as in combined state in the form of Nitrates.

Preparation Of Nitrogen By Industrial Methods

Industrially, Nitrogen is prepared by the fractional distillation of liquified air which involves following steps:

(a) Purification of air - Air is a mixture of dust particles, Carbon dioxide, Water vapour, Oxygen, Nitrogen and traces of Inert gases. Air is passed through filters to remove dust particles and then passed through soda lime (NaOH + CaO) which absorbs Carbon dioxide, and finally through anhydrous Calcium chloride to absorb moisture.

(b) Liquifaction of purified air - The purified air is repeatedly compressed, circulated through special pipes and finally it is allowed to escape through a small nozzle till the air is cooled sufficiently and finally liquified.

(c) Fractional distillation of liquified air - Liquid Nitrogen having lower boiling point distils out first leaving behind liquid Oxygen.

Preparation Of Nitrogen By Chemical Methods

In general, Nitrogen is prepared chemically:

(a) By passing Ammonia over heated Copper oxide and Lead oxide

\[3\text{CuO} + 2\text{NH}_3 \rightarrow 3\text{Cu} + \text{N}_2 + 3\text{H}_2\text{O}\]

Copper oxide and Ammonia produce Copper, Nitrogen and Water vapour

\[3\text{PbO} + 2\text{NH}_3 \rightarrow 3\text{Pb} + \text{N}_2 + 3\text{H}_2\text{O}\]

Lead oxide and Ammonia produce Lead, Nitrogen and Water vapour

(b) By mixing Chlorine with excess of Ammonia

\[8\text{NH}_3 + 3\text{Cl}_2 \rightarrow 6\text{NH}_4\text{Cl} + \text{N}_2\]

Ammonia and Chlorine produce Ammonium chloride and Nitrogen

(c) Ammonia is burnt in atmosphere of Oxygen. It burns with green flame.

\[4\text{NH}_3 + 3\text{O}_2 \rightarrow 2\text{N}_2 + 6\text{H}_2\text{O}\]

Ammonia and Nitrogen produce Nitrogen and Water

(d) By passing Ammonia over bleaching powder

\[3\text{CaCl}_2 + 2\text{NH}_3 \rightarrow 3\text{CaCl}_2 + 3\text{H}_2\text{O} + \text{N}_2\]

Bleaching powder and Ammonia produce Calcium chloride, Water and Nitrogen

Teacher's Note

Nitrogen's role in industry is crucial - it's used to create fertilizers that feed billions of people worldwide, making it one of the most important elements in modern agriculture and manufacturing.

(e) By heating Ammonium dichromate

\[(\text{NH}_4)_2\text{Cr}_2\text{O}_7 \rightarrow \text{Cr}_2\text{O}_3 + 4\text{H}_2\text{O} + \text{N}_2\]

(f) In laboratory, Nitrogen is prepared by heating the solution of Ammonium chloride and Sodium nitrite. In solid state, they are not heated because Ammonium chloride in solid state sublimes on heating.

\[\text{NH}_4\text{Cl} + \text{NaNO}_2 \rightarrow \text{NH}_4\text{NO}_2 + \text{NaCl}\]

\[\text{NH}_4\text{NO}_2 \rightarrow \text{N}_2 + 2\text{H}_2\text{O}\]

Nitrogen cannot be obtained by heating only Ammonium nitrite as it is highly unstable and readily decomposes even at room temperature.

7. Nitrogen obtained is collected over Water as it is practically insoluble in Water.

8. Nitrogen obtained from air is more denser as compared to the Nitrogen obtained from chemicals because Nitrogen obtained from air contains traces of gases.

9. Nitrogen is a colourless, odourless, tasteless gas which is practically insoluble in water. It is non-poisonous in nature however animals die in the atmosphere of Nitrogen due to want of Oxygen.

10. Chemically, Nitrogen is non-reactive at ordinary temperature because of the presence of a triple covalent bond in its molecule.

11. Nitrogen is neutral towards litmus.

12. Nitrogen is neither combustible nor a supporter of combustion.

13. Burning metals like Calcium, Magnesium and Aluminium continue to burn in the jar of Nitrogen.

\[3\text{Mg} + \text{N}_2 \rightarrow \text{Mg}_3\text{N}_2\]

Magnesium (Burning) and Nitrogen produce Magnesium nitride

\[3\text{Ca} + \text{N}_2 \rightarrow \text{Ca}_3\text{N}_2\]

Calcium (Burning) and Nitrogen produce Calcium nitride

\[2\text{Al} + \text{N}_2 \rightarrow 2\text{AlN}\]

Aluminium (Burning) and Nitrogen produce Aluminium nitride

These metallic nitrides are warmed with water to produce their respective hydroxides with the liberation of Ammonia gas.

14. Ammonia is synthesized from its elements, i.e., Nitrogen and Hydrogen by Haber's process.

\[\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3 + \text{heat}\]

15. Nitrogen combines with Oxygen at 3000°C or during thunder and lightning to form Nitric oxide.

\[\text{N}_2 + \text{O}_2 \xrightarrow{\text{electric arc}} 2\text{NO}\]

Nitrogen and Oxygen produce Nitric oxide

16. Nitrogen reacts with Calcium carbide at 1000°C to form Nitrolim which is an important fertilizer.

\[\text{CaC}_2 + \text{N}_2 \xrightarrow{1000 \text{ °C}} \text{CaCN}_2 + \text{C}\]

Calcium carbide and Nitrogen produce Calcium cyanamide (Nitrolim) and Carbon

17. The molecular formula of Ammonia is NH₃. The relative molecular mass is 17.

18. Ammonia is a polar covalent compound.

Electron dot diagram of Ammonia with Lone pair of electron

19. Ammonia is found in free state in traces.

20. In combined state Ammonia is found in the form of Ammonium salts like Ammonium chloride, Ammonium sulphate etc.

21. The smell of Ammonia in toilets is due to the bacterial decomposition of urea present in urine.

\[\text{NH}_2\text{CONH}_2 + 2\text{H}_2\text{O} \rightarrow 2\text{NH}_3 + \text{H}_2\text{O} + \text{CO}_2\]

Teacher's Note

Ammonia's pungent smell in bathrooms comes from urea breakdown by bacteria - a natural process that shows how chemistry happens constantly in our everyday environments.

22. Preparation of Ammonia: Generally, Ammonia is prepared by the following methods:

(a) In laboratory Ammonia is prepared by heating ammonium salts (Except ammonium nitrate) with caustic alkalis like sodium hydroxide, potassium hydroxide or calcium hydroxide.

\[\text{Ca(OH)}_2 + 2\text{NH}_4\text{Cl} \rightarrow \text{CaCl}_2 + 2\text{NH}_3 + 2\text{H}_2\text{O}\]

Calcium hydroxide and Ammonium chloride produce Calcium chloride, Ammonia and Water

\[\text{NaOH} + \text{NH}_4\text{Cl} \rightarrow \text{NaCl} + \text{NH}_3 + \text{H}_2\text{O}\]

Sodium hydroxide and Ammonium chloride produce Sodium chloride, Ammonia and Water

(i) The reactants are finely ground and then taken in a round bottom flask. The round bottom flask is fitted in a slanting position bending in the downward direction.

(ii) Ammonia is dried by passing over Quick lime, i.e., Calcium oxide. It is not dried by passing through conventional drying agents like cone, Sulphuric acid, anhydrous Calcium chloride, Phosphorus pentaoxide because these drying agents undergo chemical reaction with ammonia.

\[2\text{NH}_3 + \text{H}_2\text{SO}_4 \rightarrow (\text{NH}_4)_2\text{SO}_4\]

\[\text{CaCl}_2 + 8\text{NH}_3 \rightarrow \text{CaCl}_2.8\text{NH}_3\]

\[6\text{NH}_3 + 3\text{H}_2\text{O} + \text{P}_2\text{O}_5 \rightarrow 2(\text{NH}_4)_3\text{PO}_4\]

(iii) Ammonia is collected by downward displacement of air as the gas is lighter than air and highly soluble in water.

(iv) Ammonium nitrate is not used for the preparation of Ammonia as it is explosive and gives Nitrous oxide and water.

\[\text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O}\]

(b) Action of warm water on metallic nitrides (Fig. 2)

Magnesium nitride, Calcium nitride and Aluminium nitride on warming with water produces their respective metallic hydroxide with the liberation of Ammonia.

\[\text{Mg}_3\text{N}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{Warm}} 3\text{Mg(OH)}_2 + 2\text{NH}_3\]

\[\text{Ca}_3\text{N}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{Warm}} 3\text{Ca(OH)}_2 + 2\text{NH}_3\]

\[\text{AlN} + 3\text{H}_2\text{O} \xrightarrow{\text{Warm}} \text{Al(OH)}_3 + \text{NH}_3\]

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