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OXIDES OF NITROGEN

DINITROGEN OXIDE

Dinitrogen oxide or nitrous oxide is a colourless gas. N₂O is known as “laughing gas’. When inhaled, it causes a feeling of lightheadedness and gaiety. It has been used as an anesthetic. It has the following characteristics

• Density 1.97 g/dm³
• Melting point -90.8 ^OC
• Boiling point -88.5 ^OC
• Soluble in cold water (sparingly soluble in hot water), ethanol and sulphuric acid

PREPARATION

It is prepared by the controlled heating of ammonium nitrate to 250^OC

NH₄NO₃ è N₂O + 2H₂O

In this case it is advisable to use NaNO₃ instead of NH₄NO₃ , because the latter is liable to an explosion if heated above 250^OC.

2NaNO₃ + (NH₄)₂SO₄ è N₂O + 2H₂O + Na₂SO₄

CHEMICAL PROPERTIES

1. Oxidising action

N₂O + Cu(Hot) è CuO + N₂

2. Reducing action

5N₂O + 2KmnO₄ + 3H₂SO₄ è K₂SO₄ + 2MnSO₄ + 3H₂O + 10NO

NOTE: The N₂O molecule is linear and unsymmetrical, having the structure

N = N - O :

NITROGEN MONOXIDE

Nitrogen monoxide or nitric oxide is a colourless gas. It is charecterised by

• It is a colourless gas ( however in solid state it is a blue coloured mass)
• Melting point -90.8^OC
• Boiling point -88.5^OC
• It is soluble in water, ethanol and ether
• It is paramagnetic sue to the presence of one unpaired electron in the molecule.
• It is neutral towards litmus

PREPARATION

1. 1. In the laboratory it is prepared by the action of dilute Nitric acid on Copper

   3Cu + 8HNO₃ è 3Cu(NO₃)₂ + 4H₂O + 2NO

   NOTE: The gas thus formed is impure ( it contains a mixture of NO₂, N₂O and NO). it is purified by passing the impure mixture through Ferrous sulphate solution.

   2. Ostwald’s method: By the catalytic oxidation of ammonia

_{750 -900 OC\6atm}

4NH3 + 5O2 è 4NO + 6H2O

^{Pt gauze}

CHEMICAL PROPERTIES

1. it is readily oxidised to NO₂

2NO + O₂ è 2NO₂

2. it is readily reduced

2Cu + 2NO è 2CuO + N₂

3. it can be oxidised also

2NO + X_{2 è} 2NOX

USES

1. It is used in the manufacture of nitric acid, as an intermediate

2. As a catalyst in the manufacture of sulphuric acid ( in the lead chamber process)

Nitrogen (II) oxide:

NOTE: As shown by the molecular orbital diagram. the NO molecule has one unpaired electron and a bond order of 2.5. However, the molecule does not dimerise to N₂O₂.

Discuss Oxides of Nitrogen