Chemical Properties of Boron Family - Practice Questions & MCQ

Reaction towards air
Boron is unreactive in crystalline form. Aluminium forms a very thin oxide layer on the surface which protects the metal from further attack. Amorphous boron and aluminium metal on heating in air form B₂O₃ and Al₂O₃ respectively. With dinitrogen at a high temperature they form nitrides.

Where E is an element

The nature of these oxides varies down the group. Boron trioxide is acidic and reacts with basic (metallic) oxides forming metal borates. Aluminium and gallium oxides are amphoteric and those of indium and thallium are basic in their properties.

Reactivity towards acids and alkalies
Boron does not react with acids and alkalies even at moderate temperature; but aluminium dissolves in mineral acids and aqueous alkalies and thus shows amphoteric character. Aluminium dissolves in dilute HCl and liberates dihydrogen.

However, concentrated nitric acid renders aluminium passive by forming a protective oxide layer on the surface.
Aluminium also reacts with aqueous alkali and liberates dihydrogen.

Reactivity towards halogens
These elements react with halogens to form trihalides (except TlI₃).