Modern inorganic chemistry

THE ELEMENTS OF GROUP III 143

less importance, aluminium chloride vapour is passed through the

fused oxide at about 1300 K, when the following reaction occurs:

2A1 2 O 3 + 2A1C1 3 -> 6A1C1 + 3O 2

The aluminium monochloride vapour is unstable when cooled and

disproportionates (p. 77) below 1100 K thus:

3A1C1 -» A1C1 3 + 2A1

The aluminium trichloride is then re-cycled through the fused oxide.

Gallium, indium and thallium

Each of these elements can be extracted by reduction of the respec-

tive oxide at high temperature, using either carbon or hydrogen; or

by electrolysis of an aqueous solution of a salt of the required element.

REACTIONS OF THE ELEMENTS WITH ACIDS

Boron, being chemically a non-metal, is resistant to attack by non-

oxidising acids but the other members of the group react as typical

metals and evolve hydrogen. Aluminium, gallium and indium are

oxidised to the + 3 oxidation state, the simplified equation being

2M + 6H+ ^2M^3 + + 3H 2

However, thallium is oxidised to the + 1 oxidation state:

2T1 + 2H + -^2T1+ + H 2
Strong oxidising acids, for example hot concentrated sulphuric acid
and nitric acid, attack finely divided boron to give boric acid H 3 CO 3.
The metallic elements behave much as expected, the metal being
oxidised whilst the acid is reduced. Bulk aluminium, however, is
rendered "passive' by both dilute and concentrated nitric acid and
no action occurs; the passivity is due to the formation of an im-
pervious oxide layer. Finely divided aluminium does dissolve slowly
when heated in concentrated nitric acid.

REACTIONS OF THE ELEMENTS WITH ALKALIS

(SODIUM HYDROXIDE)

Amorphous boron and the amphoteric elements, aluminium and
gallium, are attacked by aqueous solutions of sodium hydroxide and