3.Answer with respect to extraction of aluminium:
1. Name the process used for concentration of aluminium.
II. Why conc. Caustic soda is used in the process?
III. Write the chemical equations involved in the process.
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Answer:
Concentration of ore is done by baeyer's process using chemical method.
The electrolytic reduction of alumina is done by hall heroult's process. The reaction at cathode is : 2Al
3+
+6e
−
→2Al Thus pure aluminium metal is formed at the cathode.
Cryolite is sodium aluminium fluoride (Na
3
AlF
6
). It ia an ore of aluminium. Cryolite and fluorspar acts as an solvent.
Al(OH)
3
→Al
2
O
3
+water
The oxygen evolved at the anode escapes as a gas or reacts with the carbon anode. The anode is thus oxidized to carbon monoxide which either burns giving CO
2
or escapes. Thus, anode has to be replaced as it is consumed periodically.The process of concentration of bauxite is known as Bayer's process.
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