Page 207 - Chemistry ICSE Class X

Metallurgy 193
ƒ Pure aluminium is a silvery-white metal. However, the commonly
available aluminium is bluish-white metal.
ƒ Aluminium is very ductile and malleable. It has high tensile strength.
ƒ Aluminium is a good conductor of heat and electricity.
ƒ Aluminium is a light (low-density) metal.
ƒ Aluminium can be cast and welded.

What are the chemical properties of aluminium Aluminium sheets
ƒ Electropositive nature. Aluminium is strongly electropositive
element. Its atom readily loses three electrons to give a tripositive
cation Al. Aluminium (Al) therefore, acts as a strong reducing agent.
3+
Al o Al + 3e –
ƒ Action of air. At ordinary temperatures, air has no action on
aluminium. In moist air, a thin protective layer of oxide is formed.
When heated to redness, it burns with a brilliant white light with the
evolution of heat.
burns
4Al + 3O o 2Al O + Heat + Brilliant white light
2
3
2
aluminium aluminium oxide
red hot
When burnt in air, aluminium also forms aluminium nitride (AlN). tĂƚĞƌ ĐŽŶƚĂŝŶŝŶŐ ĞůĞĐƚƌŽůLJƚĞƐ
ƒ Action of water. Pure water has no action on aluminium in cold. ĐŽƌƌŽĚĞƐ ĂůƵŵŝŶŝƵŵ ƉĂƌƟĐƵůĂƌůLJ
Aluminium decomposes boiling water to liberate hydrogen. ǁŚĞŶ ŝƚ ŝƐ ŚŽƚ͘
heat
2Al + 6H O(boiling) o 2Al(OH) + 3H (g)
2
2
3
ƒ Action of nitrogen. On heating with nitrogen, it forms aluminium
nitride.
heat
2Al(s) + N (g) o 2AlN(s)
2
aluminium nitride
ƒ Action of chlorine. When chlorine is passed over heated aluminium,
its chloride is formed.
2Al + 3Cl o 2AlCl 3
2
hot aluminium chloride
ƒ Action of acids.
Š Aluminium reacts with HCl to give hydrogen.
2Al + 6HCl o 2AlCl 3 + 3H 2
Š Aluminium does not react with dil. H SO . Hot conc. sulphuric
2
4
acid gives sulphur dioxide and aluminium sulphate.
2Al + 6H SO o Al (SO ) + 3SO 2 + 6H O
2
2
4 3
2
4
(conc.)
Š Aluminium does not react with nitric acid (dilute or concentrated).
ƒ Action of alkalis. Hot solution of strong alkalis dissolve aluminium to
form aluminates and liberate hydrogen.
2Al(s) + 2NaOH(aq) + 2H O o 2NaAlO 2 + 3H (g)
2
2
aluminium sod.
metaaluminate
ƒ Action with carbon and sulphur. When heated separately with carbon
and sulphur, aluminium forms aluminium carbide and aluminium
sulphide, respectively.
'
4Al + 3C o Al C 3
4
aluminium aluminium carbide