Question

The chief ore of aluminium is bauxite which mainly contains Al₂O₃.2H₂0. The ore is initially purified before Aluminium is extracted electrolitically.

1. Identify the main impurities associated with this ore.  
2. Sodium hydroxide solution is used in the purification process. State its role.  
3. Given an equation for the reaction that forms Aluminium oxide (Alumina) from aluminium hydroxide.

Answer 1

1. Iron(III)oxide / Fe₂O₃
   Silicon(IV)oxide/ SiO₂
2. It reacts with acidic SiO₂ and amphoteric Al₂O₃ so that Fe₂O₃ is removed as red mad
3. 2Al(OH)_3(g)  Al₂O_3(s) + 3H₂O_(l)
                              ∆