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(a) Which metal is extracted from bauxite ore?
(b) Give the name of one ore of iron. Which iron compound is present in this ore? Write its chemical formula.
(c) Describe the extraction of zinc metal from its sulphide ore (zinc blende). Write an equation of the reactions involved.
(d) Explain why, the galvanised iron article is protected against rusting even if the zinc layer is broken.
(e) Name a common metal which is highly resistant to corrosion.

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Solution

(a) Aluminium metal is extracted from bauxite ore. The aluminium compound present in this ore is aluminium oxide. The chemical formula of the ore is Al2O3.2H2O

(b) Hematite is an ore of iron. The iron compound present in hematite ore is iron (III) oxide. The formula of the ore is \)Fe_2O_3\).

(c) Zinc blende (ZnS) is the sulphide ore of zinc. The extraction of zinc from zinc blende involves two steps. First, the concentrated zinc blende is converted to its oxide (by roasting). After this, the oxide is reduced to zinc metal. The reactions for the two processes are:

1. Roasting: Zinc blende is subjected to roasting, i.e. it is heated in the presence of excess air. This converts zinc sulphide ore to zinc oxide.
The reaction involved is:
2ZnS(s)+3O2(g)Roasting (surplus of air)−−−−−−−−−−−−−−2ZnO(s)+2SO2(g)
2. Reduction: Zinc oxide is then reduced by coke (carbon). When zinc oxide is heated with coke, carbon acts as a reducing agent and reduces zinc oxide to zinc metal.
ZnO(s)+C(s)reduction−−−−Zn(s)+CO(g)

(d) The galvanised iron-zinc oxide layer coating on iron objects prevents zinc and iron under it from corrosion. This happens because zinc is more reactive than iron. If the zinc layer is broken, zinc, being more reactive, gets oxidised before iron and prevents its corrosion.

(e) Aluminium is a common metal that is highly resistant to corrosion because it is a highly reactive metal. It reacts easily with oxygen in the air and forms a layer of aluminium oxide on its surface. This aluminium oxide layer is very tough and does not allow air to enter the metal for further reaction, thus preventing further corrosion of aluminium.


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