Modern inorganic chemistry

222 GROUPV

(NH 4 ) 2 Cr 207 -* N 2 + 4H 2 O + Cr 2 O 3

NH 4 NO 3 -» N 2 O + 2H 2 O

The mixture of ammonium nitrate and powdered aluminium is an

explosive known as ammonal.

Uses of ammonia and ammonium compounds. Most of the ammonia

produced is used in the manufacture of nitrogenous fertilisers such

as ammonium sulphate. Other uses include nitric acid and synthetic

fibre and plastic manufacture.

DETECTION OF AMMONIA AND AMMONIUM SALTS

All ammonium salts evolve ammonia on heating with alkali.
Ammonia may be detected by (a) its smell, (b) its action in turning
red litmus blue and (c) the orange-brown colour produced with
Nessler's reagent. This is a very sensitive test.
Ammonia may be estimated by dissolving the gas in a known
volume of standard acid and then back-titrating the excess acid. In a
method widely used for the determination of basic nitrogen in organic
substances (the Kjeldahl method), the nitrogenous material is con-
verted into ammonium sulphate by heating with concentrated
sulphuric acid. The ammonia is then driven off by the action of
alkali and absorbed in standard acid.
Ammonia present in very small quantities in solution may be
estimated by comparing the intensity of colour produced with
Nessler's reagent (p. 439) with standard colours, using a simple form
of colorimeter called a 'Nessleriser'.

Hydroxylamine, NH 2 OH

Hydroxylamine is derived from ammonia by replacing one hydrogen
atom by a hydroxyl group. It is prepared by the electrolytic reduction
of nitric acid, using a lead cathode :
HNO 3 4- 6H+ + 6e~ -» NH 2 OH 4- 2H 2 O
Sulphuric acid is added to the electrolyte and the hydroxylamine
is formed as hydroxylammonium sulphate, (NH 3 OH) 2 SO 4 [cf.
(NH 4 ) 2 SO 4 ]. Addition of barium chloride then precipitates barium
sulphate and hydroxylammonium chloride, (NH 3 OH)C1, is obtained.
Pure hydroxylamine is a crystalline solid of low melting point
(306 K) but is rarely prepared because it decomposes above 288 K