Write three balanced equations for the purification of bauxite by Hall's process.

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Solution

Aluminum is extracted from its principle ore, bauxite. In Hall's process, molten cryolite and fluorspar are used to dissolve pure alumina.
Balanced equations for the purification of bauxite by Hall's process:
In Hall's process, the ore is fused with sodium carbonate followed by hydrolysis and heating.
$1) {Al}_{2} O_{3} . 2 H_{2} O (s) + {Na}_{2} {CO}_{3} (aq) \to 2 {NaAlO}_{2} (aq) + {CO}_{2} (g) + 2 H_{2} O (l) baxuite sodium sodium meta carbonate aluminate 2) 2 {NaAlO}_{2} (aq) + {CO}_{2} (g) + 3 H_{2} O (l) \to 2 Al {(OH)}_{3} (s) + {Na}_{2} {CO}_{3} (aq) aluminium sodium hydroxide carbonate 3) 2 Al {(OH)}_{3} (s) \overset{∆}{\to} {Al}_{2} O_{3} (s) + 3 H_{2} O (l) Alumina$

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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:

(i) the aluminium oxide,

(ii) the iron (III) oxide?

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(ii) Write the equation for the action of heat on aluminium hydroxide.

(ii) Write down the word which correctly completes the following sentence.By dissolving aluminium oxide in cryolite a ..........(conducting/non conducting) solution is produced.

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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.
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