During the extraction of aluminium by Hall-Héroult process, cryolite (Na₃AlF₆) is added to alumina to:
A. Increase the yield of aluminium
B. Lower the melting point and increase conductivity
C. Prevent corrosion
D. Act as catalyst
Answer: Option B
Solution (By JKExamLibrary)
Alumina has a very high melting point (~2050°C). Cryolite (and fluorspar) is mixed to form a molten mixture with lower melting point (~950°C) and better electrical conductivity, enabling electrolytic reduction. The electrolyte is a solution of alumina in molten cryolite. Carbon anodes are consumed. This reduces energy consumption.
Explanation:
Oxidation is loss of electrons. Na loses an electron to become Na⁺, so it is oxidized. Options A, C, D involve gain of electrons (reduction). Oxidation also can be defined as gain of oxygen or loss of hydrogen. In the reaction, Na acts as reducing agent. Mnemonic: LEO (Loss of Electrons is Oxidation) GER (Gain of Electrons is Reduction).
Explanation:
Copper pyrites (CuFeS₂) is a sulfide ore, concentrated by froth flotation using pine oil and water. Then roasting, smelting, and refining.
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