Bauxite is the principal ore used in the commercial extraction of aluminium. The Bayer's process is used to refine bauxite into pure alumina, with caustic soda playing a crucial role in the initial stage of the process.
Based on this, answer the following questions:
(a) Explain the reason behind the addition of caustic soda during the Bayer's process.
(b) Write a balanced chemical equation representing the reaction between bauxite and caustic soda during the Bayer's process.
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(a) Bauxite contains alumina along with impurities such as ferric oxide and sand. Alumina is amphoteric and dissolves in hot concentrated caustic soda to form soluble sodium meta-aluminate, while the insoluble impurities remain as red mud and are removed by filtration.
(b) Al2O3·2H2O + 2NaOH ⟶ 2NaAlO2 + 3H2O