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Question
4 tones of bauxite, 150 Kg of sodium hydroxide and 600 Kg of graphite.
The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (II) oxide. Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.
(a) When bauxite is treated with sodium hydroxide solution, what happens to:
(i) the aluminium oxide?
(ii) The iron (III) oxide?
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Solution
(i) Aluminium oxide being an amphoteric oxide reacts with sodium hydroxide solution to form soluble sodium meta aluminate.
\[\ce{\underset{\text{Alumina}}{Al2O3.2H2O} + 2NaOH + 2H2O ->\underset{\text{Sodium aluminate}}{2NaAIO2} + 3H2O}\]
(ii) Iron (III) oxide remains undissolved in the sodium hydroxide solution and settles down.
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In order to obtain one tone of aluminium, the following inputs are required:
4 tones of bauxite, 150 Kg of sodium hydroxide and 600 Kg of graphite.
The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (II) oxide. Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.
(i) Write the formula of cryolite.
(ii) Write down the word which correctly completes the following sentence.
"By dissolving aluminium oxide in cryolite, a ______ (conducting / non- conducting) solution is produced.
(iii) Why so much graphite required for this electrolytic process.
(iv) Write the equation for the reaction which takes place at cathode.
Name two metallic oxides which cannot be reduced by carbon, carbon monoxide or hydrogen.
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