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Question
The following is an extract from metals in the service of man, Alexander and street /Pelican 1976': Alumina (aluminium oxide) has a very high melting point over 2000oC, so that I cannot readily be liquefied. However, conversion of alumina to aluminium and oxygen, by electrolysis, an occur when it is dissolved in some other substance.
(a) Which solution is used to react with bauxite as first step in obtaining pure aluminium oxide?
(b) The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the equation for this reaction.
(c) Name the element which serves both as the anode and the cathode in the extraction of aluminium.
(d) Write the equation for the reaction that occurs at the cathode during the extraction of aluminium.
(e) Write the equation for the reaction that occurs at the cathode during extraction of aluminium by electrolysis.
(f) Give the equation for the reaction that occurs at the anode when aluminium is purified by electrolysis.
Solution
(a) Bauxite is reacted with sodium hydroxide to obtain pure aluminium oxide.
(b) 2Al(OH)3 → Al2O3 + 3H2O
(c) Carbon serves both as anode and cathode.
(d) Reaction at cathode :
Al+3 + 3e- → Al
(e) Reaction at cathode :
Al+3 + 3e- → Al
(f) Reaction at anode :
O-2 - 2e- → O
O + O → O2
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