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Question
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.
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Solution
(i) Na3AIF6. It is also known as Sodium aluminium fluoride.
(ii ) Conducting solution is produced.
(iii ) Because it reacts with O2, produced at anode and gets consumed to form CO2.
O2- - 2e- → [O]
C + 2[O] → CO2
So carbon rods are replaced from time to time.
(iv) 2Al3+ + 6e- → 2AI
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