Chemistry
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.
Related Questions
For each substance listed below, explain it's significance in the extraction of aluminium:
(a) Bauxite
(b) Sodium hydroxide
(c) Cryolite
(d) Graphite
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?
(a) A to F below relate to the source and extraction of either zinc or aluminium:
A. Bauxite
B. Coke
C. Cryolite
D. Froth floatation
E. Sodium hydroxide solution
F. Zinc blende
(i) Write down the three letters each from the above list which are relevant to
- Zinc
- Aluminium
(ii) Fill in the blanks using the most appropriate words from A to F.
The ore from which aluminium is extracted must first be treated with …………… so that pure aluminium oxide can be obtained.
Pure aluminium oxide is dissolved in …………… to make a conducting solution.
(iii) Write the formula of cryolite.
With respect to the Hall Heroult process, justify the following:
(a) Powdered coke is sprinkled over the electrolytic mixture undergoing electrolytic reduction.
(b) Graphite anodes are continuously replaced during the electrolysis.
(c) Cryolite and fluorspar must be added to the electrolytic mixture.
(d) Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.