P-Block Element and Their Compound – I: Ammonia and Chemical Reaction (For CBSE, ICSE, IAS, NET, NRA 2022)

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Ammonia

Preparation

Ammonia is prepared in the laboratory by heating an ammonium salt with a base.

It can be prepared by treating a nitride with water.

Industrially, it is prepared by passing nitrogen and hydrogen over an iron catalyst at and under a pressure of about 200 atmospheres.

  • In the actual process the hydrogen required is obtained from water gas and nitrogen from the fractional distillation of liquid air.
  • A typical plant might be arranged as shown in Fig.
Ammonia is Prepared in the Laboratory

Properties

  • Ammonia is a colorless and pungent smelling gas.
  • Ammonia is readily liquefied at pressure of about nine atmospheres at ordinary temperatures.
  • Ammonia is extremely soluble in water.
  • The hydrated ammonia molecule, , is loosely called ammonium hydroxide .

Chemical Reaction

Action of heat: When heated above 5000C it begins to decompose into elements.

With oxygen: Ammonia does not burn in air but freely burns in pure oxygen with a yellowish flame giving nitrogen and steam.

As a reducing agent: If ammonia is passed over those heated metallic oxides which are reducible by hydrogen, e. g. , , etc. it is oxidized to nitrogen and water.

With acids: It is easily absorbed by acids to form ammonium salts, e. g.

With chlorine: Ammonia reacts with chlorine, the products varying with conditions.

(with excess of ammonia)

(with excess of chlorine)

With metal salts: With some metal salts, aqueous ammonia reacts to form metal hydroxides which are precipitated. For example,

Uses

  • Ammonia is used in the manufacture of ammonium sulphate for use as a fertilizer.
  • Ammonia is used in the manufacture of nitric acid (Ostwald process)
  • Liquid ammonia is used in refrigerators.
  • Ammonia is used in the manufacture of sodium carbonate by Solvay process.

Structure

  • Ammonia molecule is trigonal pyramid with the nitrogen at the apex.
  • The nitrogen atom is hybridized in which a lone pair of electrons occupies one of the tetrahedral positions.
  • The angle becomes instead of due to lone pair-bond pair repulsion (Fig) .
Ammonia Molecule

Oxoacids of Nitrogen

There are several oxoacids of nitrogen such as nitrous acid, , hyponitrous acid, and nitric acid, .

Developed by: