Properties of Aluminium
(i) It
is a silvery metal with a density of 2.7 g/cc, having a melting point of 660oC, and is a
good conductor of heat and electricity. It is malleable and ductile.
(ii) Action
of air: Dry air has no action on aluminium. But moist air forms a thin
layer of Al2O3 on its surface and it loses its luster. At
very high temperatures it burns to form Al2O3 and AlN.
(iii) Reaction
with halogens : When gaseous halogens are passed over aluminium, its
halide are formed in an anhydrous form.
2Al
+ 3Cl2
2AlCl3
(iv) Action
of alkalies: When warmed with concentrated NaOH, it liberates H2 gas and a colourless solution of sodium
meta-aluminate is formed.
2Al + 2NaOH + 2H2O
2NaAlO2 + 3H2
(v) Action
of acids: Aluminium reacts with dilute H2SO4 and dilute HCl but concentrated HNO3 does not react with aluminium because
aluminium becomes passive by the action of concentrated HNO3 forming
a protective oxide layer on the surface.
2Al + 3H2SO4
Al2(SO4)3 + 3H2 ; 2Al + 6HCl
2AlCl3 + 3H2
(vi) Reaction
with N2: When N2 gas is
passed over heated aluminium, aluminium nitride is formed. Hot aluminium thus
acts as an absorbing agent for N2.
2Al + N2
2AlN
AlN
reacts with hot water to form Al(OH)3 and NH3
(vii) Reaction
with water: Aluminium does not react with cold water. It is very slowly
attacked by boiling water or steam.
2Al + 6H2O
2Al(OH)3 + 3H2
(viii) Reduction
of oxides of metals : When oxides of less reactive metal than aluminium
is heated with aluminium, the other metal is liberated.
3MnO2 + 4Al
2Al2O3 + 3Mn; Cr2O3 + 2Al
Al2O3 + 2Cr
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