Chemistry
For each substance listed below, explain it's significance in the extraction of aluminium:
(a) Bauxite
(b) Sodium hydroxide
(c) Cryolite
(d) Graphite
Answer
(a) Bauxite — Main ore from which aluminium is extracted. It contains 60% Al2O3
(b) Sodium hydroxide — Sodium hydroxide is used in the purification of bauxite ore by converting it into alumina. It acts as an effective solvent for the aluminum oxide in bauxite and helps to remove impurities like ferric oxide, sand, etc. which are collectively called as red mud.
(c) Cryolite — Lowers the fusion temperature from 2050°C to 950°C. and enhances conductivity.
(d) Graphite — Thick Graphite rods attached to copper clamps dipping into fused electrolyte are used as anode.
Related Questions
Explain with reasons:
A neutral gas other than oxygen is formed at the anode during electrolysis of fused alumina.
Explain with reasons:
Why is powdered coke sprinkled on top of the electrolyte?
In order to obtain 1 tonne of aluminium, the following inputs are required: 4 tonnes 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 (III) 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
(b) (i) Name the process used for the purification of bauxite.
(ii) Write the equation for the action of heat on aluminium hydroxide.
(c) (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 is so much graphite required for the electrolytic process?
(iv) Write the equation for the reaction which takes place at the cathode
(v) What is the cathode made up of?
Aluminium is extracted from it's chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.
(a) Name a chemical used for dissolving aluminium oxide. In which state is the chemical used?
(b) State the reason for addition of caustic alkali to bauxite ore during the purification of bauxite.
(c) Write three balanced equations for the purification of bauxite.
(d) Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process.