144 THE ELEMENTS OF GROUP III
hydrogen is liberated. Boron reacts slowly with boiling concentrated
sodium hydroxide to give sodium polydioxoborate (metaborate)
Na*(BOj)n. but both aluminium and gallium will react at room
temperature to produce hydroxo-aluminate and hydroxo-gallate
ions respectively:2A1 + 2NaOH + 10H 2 O -> 2Na+[Al(OH) 4 (H 2 O) 2 ]" + 3H 2The more metallic elements, indium and thallium, do not react in
spite of the fact that In(OH) 3 is amphoteric.REACTIONS OF THE ELEMENTS WITH WATER
Neither boron nor aluminium reacts with water at room tempera-
ture but both react with steam at red heat liberating hydrogen:
2B + 6H 2 O -> 2H 3 BO 3 + 3H 22A1 + 3H 2 O -> A1 2 O 3 + 3H 2The electrode potential of aluminium would lead us to expect
attack by water. The inertness to water is due to the formation of
an unreactive layer of oxide on the metal surface. In the presence
of mercury, aluminium readily forms an amalgam (destroying the
original surface) which is. therefore, rapidly attacked by water.
Since mercury can be readily displaced from its soluble salts by
aluminium, contact with such salts must be avoided if rapid corro-
sion and weakening of aluminium structures is to be prevented.
In the absence of oxygen, gallium and indium are unaffected by
water. Thallium, the most metallic element in Group III, reacts
slowly with hot water and readily with steam to produce thallium(I)
oxide, T1 2 O.
REACTIONS OF THE ELEMENTS WITH AIR
Only thallium of the Group III elements is affected by air at room
temperature and thallium(III) oxide is slowly formed. All the
elements, however, burn in air when strongly heated and, with the
exception of gallium, form the oxide M 2 O 3 : gallium forms a mixed
oxide of composition GaO. In addition to oxide formation, boron
and aluminium react at high temperature with the nitrogen in the
air to form nitrides (BN and AIM).