1.

Name the principal ore of aluminium and describe how Al is extracted from its ore. 

Answer»

Important ores -(i) Bauxite Al2O3.xH20 (ii) Corrundum Al2O3. Bauxite is commercially important ore Al. 

Extraction from Bauxite ore involves the following two stages:

(i) Purification of bauxite to get pure alumina (Al2O3) 

(ii) Electrolysis of pure alumina in molten cryolite 

Step:1 Bauxite is treated with NaOH. Following reaction takes place

Al2O3 +2NaOH + 3 H2O → 2Na [Al(OH)4] and impurities of Fe2O3,TiO2 &SiO2 are removed . 

Na [Al(OH)4] ,then reacts with CO2 then pure Alumina is obtained.                  

Na [Al(OH)4] + 2CO2 → Al2O3.xH2O + 2NaHCO3     

Step:2 Electrolytic reduction of pure alumina takes place in iron box (cathode) with cryolite (Na3AlF6) & fluorspar CaF2. Graphide rods act as anode. Following reactions take place:- 

At cathode:‐ Al3+  + 3e → Al, 

At Anode:‐ 2O2‐ →O2+                                                     

By this process 98.8% pure Aluminum is obtained. 


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