Question

Describe the role played in the extraction of aluminum:
Sodium hydroxide

Answer 1

In the extraction of aluminium, the given compounds play the following roles:

Sodium hydroxide :
Two roles are played by sodium hydroxide in the extraction of aluminium.
First, finely grinded bauxite (ore of aluminium) is heated under pressure with conc. caustic soda solution (NaOH solution) for 2-8 hours at 140°C to 150°C to produce sodium aluminate. The chemical equation is as follows:

Al₂O₃.2H₂O + 2NaOH → 2NaAlO₂+ 3H₂O

Second, on diluting sodium aluminate with water and cooling to 50°C, sodium aluminate is hydrolysed to give aluminium hydroxide as a precipitate. Here, the impurities dissolve in sodium hydroxide.