Chemistry Reference
In-Depth Information
Using cheap electrical energy has allowed aluminium
to be produced in such large quantities that it is
the second most widely used metal after iron. It is
used in the manufacture of electrical cables because
of its low density, chemical inertness and good
electrical conductivity. Owing to the fi rst two of
these properties, it is also used for making cars,
bikes, cooking foil and food containers as well as
in alloys (Chapter 10, p. 167) such as duralumin,
which is used in the manufacture of aeroplane bodies
(Figure 5.8). Worldwide production of aluminium
now exceeds 40 million tonnes each year.
Figure 5.9
Bauxite pollution of the Amazon in Brazil.
•
the claimed link between environmental
aluminium and a degenerative brain disorder
called Alzheimer's disease - it is thought that
aluminium is a major infl uence on the early onset
of this disease. However, the evidence is still
inconclusive.
Questions
1
Produce a fl ow chart to summarise the processes involved
in the extraction of aluminium metal from bauxite.
2
Explain why the mixture of gases formed at the anode
contains oxygen, carbon dioxide and traces of fl uorine.
Anodising
This is a process in which the surface coating of
oxide on aluminium (Al
2
O
3
) is made thicker. In this
process the aluminium object is made the anode in
a cell in which the electrolyte is dilute sulfuric acid.
During the electrolysis process, oxygen is produced
at the anode and combines with the aluminium.
The oxide layer on the surface of the aluminium
therefore increases. Dyes can be mixed with the
electrolyte and so the new thicker coating of oxide is
colourful and also decorative (Figure 5.10).
Figure 5.8
Aluminium is used in the manufacture of aeroplane bodies.
Environmental problems associated with the location
of aluminium plants are concerned with:
•
the effects of the extracted impurities, which form
a red mud (Figure 5.9)
•
the fi ne cryolite dust, which is emitted through
very tall chimneys so as not to affect the
surrounding area
