204 ALKALI AND ALKALINE EARTH METALS
AMMONIUM COMPOUNDS
When ammonium hydroxide dissociates electrolytically it yields
the ion NIL/^1 ". The group of atoms NH 4 , which is often spoken
of as the ammonium radical, resembles in many respects the atom
of sodium or potassium. Like these, it can form a monovalent
positive ion, or it can form compounds with acid radicals, for
example, NH4CI, (NH^SCV, but unlike sodium and potassium,
it cannot exist in the uncombined state.
- (a) Place a mixture of dry ammonium chloride and
calcium hydroxide in a dry test tube and heat gently. A gas
escapes from the tube, which has the odor of ammonia and
which turns moist litmus blue.
(6) Add a solution of a strong base to a solution of any
ammonium salt, warm. The odor of ammonia is at once
apparent.
These experiments furnish an example of the displacement of
a weak base by means of a strong base. In (a) there is doubtless
enough moisture condensed on the surface of the solid material so
that the reaction can be considered as an ionic one. In this
case as well as in (6) we have the weak base NH4OH forming from
its ions. The non-electrolytic dissociation of NH4OH yields the
gas NH 3 , the odor of which is observed.- Gaseous Dissociation of Ammonium Chloride. Like all
ammonium salts, ammonium chloride can be volatilized by
applying heat. Some of the other salts are permanently de-
composed by the process, but the vapor of ammonium chloride
can be condensed again to the same solid substance.
Place 2 grams of ammonium chloride in the middle of a
combustion tube, and on either side place loose plugs of
asbestos. Outside the asbestos plugs at both ends place mois-
tened strips of both red and blue litmus paper. Support
the tube in a slightly inclined position by means of a clamp,
and heat the section containing the salt, using a flame spreader.
At both ends the red litmus is colored blue at first. Later
the color at each end changes to red.
The vapor of ammonium chloride is very largely dissociated
non-electrolytically
NH4CI ^ NH 3 + HC1