In the extraction of aluminium from bauxite, the reagent used to remove silica as an impurity is:
A. CO
B. Cl₂
C. NaOH
D. HCl
Answer: Option C
Solution (By JKSSB Mock Tests)
Bauxite contains SiO₂ (silica) as impurity. In the Bayer's process, powdered bauxite is treated with hot concentrated NaOH solution. Alumina dissolves forming sodium aluminate (NaAlO₂), while silica does not dissolve and is filtered off. Alternatively, silica can be removed by adding lime during refining. The purified alumina is then electrolyzed in cryolite. NaOH selectively dissolves Al₂O₃ due to its amphoteric nature.
Explanation:
At anode (oxidation): 2Cl⁻ → Cl₂ + 2e⁻ (chlorine gas). At cathode (reduction): Na⁺ + e⁻ → Na (liquid sodium). In aqueous NaCl, due to water, cathode produces H₂ and anode Cl₂ (or O₂ depending on concentration).
Explanation:
The long hydrocarbon chain (tail) of soap is non-polar and hydrophobic, so it dissolves into the oily/greasy dirt particle. The ionic head (hydrophilic) remains in the water. This forms a micelle around the dirt, emulsifying it and allowing it to be washed away. The tail-dirt interaction is via van der Waals forces.
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