Aluminium is prepared industrially by Hall-Heroult process. Various steps in the concentration of ore are given below . Write them in the correct order.
i. The precipitate formed is separated , washed and strongly heated to get alumina.
ii. Crushed bauxite is leached with hot sodium hydroxide solution.
iii. Impurities are removed from the sodium aluminate solution for filtration.
iv. Solution is diluted after adding a little aluminium hydroxide , to precipitate aluminium hydroxide.

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Solution

The correct order of steps in the concentration of ore is:

(ii) Crushed bauxite is leached with hot sodium hydroxide solution.
(iii) Impurities are removed from the sodium aluminate solution for filtration.
(iv) Solution is diluted after adding a little aluminium hydroxide , to precipitate aluminium hydroxide.
(i) The precipitate formed is separated , washed and strongly heated to get alumina.

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In order to obtain 1 tonner 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:

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(ii) the iron (III) oxide?

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(iv) Write the equation for the reaction which takes palace at cathode.

Q. In order to obtain one 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 to show 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 this electrolytic process?
(iv) Write the equation for the reaction which takes place at the cathode.
(d) In construction work, why is the alloy of aluminium, duralumin used rather than pure aluminium.

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