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agents because they can displace metals of lower reactivity from their
compounds. For example, when manganese dioxide is heated with
aluminium powder, the following reaction takes place –
3MnO (s) + 4Al(s) → 3Mn(l) + 2Al O (s) + Heat
2 2 3
Can you identify the substances that are getting oxidised
and reduced?
These displacement reactions are highly exothermic. The
amount of heat evolved is so large that the metals are produced
in the molten state. In fact, the reaction of iron(III) oxide (Fe O )
2 3
with aluminium is used to join railway tracks or cracked
machine parts. This reaction is known as the thermit reaction.

Fe O (s) + 2Al(s) → 2Fe(l) + Al O (s) + Heat
2 3 2 3
3.4.5 Extracting Metals towards the Top of the
Activity Series
Figure 3.11
Figure 3.11
Figure 3.11
Figure 3.11
Figure 3.11
Thermit process for The metals high up in the reactivity series are very reactive. They cannot
joining railway tracks be obtained from their compounds by heating with carbon. For example,
carbon cannot reduce the oxides of sodium, magnesium, calcium,
aluminium, etc., to the respective metals. This is because these metals
have more affinity for oxygen than carbon. These metals are obtained
by electrolytic reduction. For example, sodium, magnesium and calcium
are obtained by the electrolysis of their molten chlorides. The metals
are deposited at the cathode (the negatively charged electrode), whereas,
chlorine is liberated at the anode (the positively charged electrode). The
reactions are –

+
At cathode Na + e – → Na
At anode 2Cl – → Cl + 2e –
2
Similarly, aluminium is obtained by the electrolytic reduction of
aluminium oxide.

3.4.6 Refining of Metals

The metals produced by various reduction processes
described above are not very pure. They contain
impurities, which must be removed to obtain pure metals.
The most widely used method for refining impure metals
is electrolytic refining.
Electrolytic Refining:
Electrolytic Refining:
Electrolytic Refining:
Electrolytic Refining:
Electrolytic Refining: Many metals, such as copper, zinc,
tin, nickel, silver, gold, etc., are refined electrolytically. In
Figure 3.12
Figure 3.12
Figure 3.12 this process, the impure metal is made the anode and a
Figure 3.12
Figure 3.12
Electrolytic refining of copper. The thin strip of pure metal is made the cathode. A solution of
electrolyte is a solution of acidified copper the metal salt is used as an electrolyte. The apparatus is
sulphate. The anode is impure copper,
whereas, the cathode is a strip of pure set up as shown in Fig. 3.12. On passing the current
copper. On passing electric current, pure through the electrolyte, the pure metal from the anode
copper is deposited on the cathode. dissolves into the electrolyte. An equivalent amount of pure
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