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प्रश्न
For the substance given below, describe the role played in the extraction of aluminium.
Sodium hydroxide
उत्तर
In the extraction of aluminium, sodium hydroxide plays two roles. 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:
\[\ce{Al2O3.2H2O + 2NaOH → 2NaAlO2 + 3H2O}\]
Second, when the sodium aluminate is diluted with water and cooled to 50°C, the sodium aluminate is hydrolysed to produce aluminium hydroxide as the precipitate. Here, the impurities dissolve in sodium hydroxide.
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