Chapter 19: Nitrogen and its compound

Introduction

• Colourless, odourless gas• 78% by volume in air• Liquid nitrogen as a coolant• Most important use is in the

manufacture of ammonia and nitrogenous fertilizers

•Can form a large number of inorganic compounds

•A major constituent of organic compounds

Extraction of nitrogen from air

• In industry,nitrogen is obtained by the fractional distillation of liquid air.

• Usually contains a little noble gases as impurities.

Clean air

compression and cooling Liquified air

Fractional distillation

N₂(g) O₂(g)

Preparation of nitrogen in laboratory

• Obtained by heating solid ammonium nitrate(III).

-NH₄NO₂(s) N₂(g)+2H₂O(g)• Free of noble gas impurities.

Chemical properties of nitrogen

• Inert under room conditions.

• Can combine with other elements to form compounds under suitable conditions.

• Nitrides of metals are hydrolysed by water to liberate ammonia gas.

• Exhibit variable oxidation states in its compounds.

Ammonia

•A colourless, pungent gas•Easily liquefied (b.p. –33oC)•Extremely soluble in water to form a weakly alkaline solution•Synthesized by Haber Process•Starting material for HNO₃ and many other important chemicals.

Physical Properties

The Haber process

• Ammonia is made by Haber Process from nitrogen&hydrogen.

-N₂(g) + 3H₂(g)   H₂NH₃(g)∆H= -92 kJ/mol• Conditions: 500˚C,200 atm.• Fe as catalyst.• Yield: about 15%

Chemical properties• Weak alkali• Ligands in Complex Formation• As a reducing agent

Ex:–Burning in oxygen4NH3 + 3O2→ 2N2 + 6H2O

–Catalytic oxidation4NH3 + 5O2 (Pt)→ 4NO +6H₂O

Uses• Use to make:

a) Fertilisers

b) Nitric acid

c) Synthetic fibres

d) Plastic

e) nylon

• Use as:

a) Refrigerant

b) Domestic cleaning agent

Oxides of nitrogen

•Nitrogen oxide -a binary compound of oxygen and nitrogen, or a mixture of such compounds.•3 important oxides:1.Nitrogen monoxide,NO

2.Nitrogen dioxide,NO₂

3.Dinitrogen tetroxide,N₂O₄

Nitric(v) Acid

Industrial Preparation of Nitric(v)Acid

• By Ostwald process:

1. Catalytic oxidation of NH3• –4NH₃+ 5O₂(Pt/heat)→ 4NO + 6H₂O2.Oxidation of NO

–2NO + O₂→ 2NO₂3.Dissolving NO₂ in water and O₂ –4NO₂ + O₂+ 2H₂O→ 4HNO₂4.Distillation to obtain 68.5% (15M) HNO₃ as

azeotrope

Colourless,viscous liquid(boils at 86˚С).A very strong acid.Turns yellow because of dissolved NO2 formed from the decomposition of HNO3.

Physical properties

Kept in amber or dark bottle to avoid exposure to light.

Weak eletrolyte due to ionisation: -2HNO₃(l) NO₂ (l)+NO₃ (l)⁺ ⁻+H₂O(l)

Chemical Properties

As a strong acidAs an Oxidising Agent

Uses• Use in the manufacture of:

1.nitrate fertilisers

2.explosives

3.organic dyes

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Exercise1. Describe the extraction of nitrogen from air. In what

aspect is the composition of the nitrogen obtained from air different from the nitrogen obtained in the laboratory by chemical means.

2. a)Describe the Haber Process in the manufacturing of ammonia.

b)Write balanced equation to illustrate the following properties of ammonia.

i. As a weak base

ii. As a ligand in complex ion formation

iii. As a reducing agent

c)Name two large-scale uses of ammonia.

i. As a weak baseii. As a ligand in complex ion

formationiii.As a reducing agent

c)Name two large-scale uses of ammonia.