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Question
How electrolysis can be used in extraction of aluminium? Why aluminium cannot be reduced by conventional reducing agents?
Solution
Aluminium is extracted by the electrolysis of fused pure alumina dissolved in fused mixture of cryolite and fluorspar. This mixtures lowers the melting point of alumina and increases the electrical conductivity and the electrolysis
is carried out in an iron tank lined with gas carbon. This lining of a gas carbon serves as cathode. The anode consists of a number of carbon rods which dip in fused electrolyte. On passing electric current following reaction takes place.
At Cathode : Al+3 + 3e-→ Al
At anode : O-2 - 2e- → O
O + O → O2
Certain metal oxides are highly stable and so cannot be reduced by conventional reducing agents like coke, carbon monoxide or hydrogen. They are extracted from their oxides or salts by the electrolysis in fused state. For e.g.; metals like aluminium, sodium, potassium, magnesium, titanium, calcium etc. are extracted by this method.
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