During the extraction of aluminium by Hall-Héroult process, cryolite (Na₃AlF₆) is added to alumina to:
A. Lower the melting point and increase conductivity
B. Act as catalyst
C. Increase the yield of aluminium
D. Prevent corrosion
Answer: Option A
Solution (By JKSSB Mock Tests)
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:
Synthetic detergents (like alkyl sulfates or sulfonates) form soluble calcium and magnesium salts, so they lather well even in hard water. Soaps form scum. Detergents are usually derived from petrochemicals, can be non-biodegradable if branched, and may cause pollution.
Explanation:
Cooking of food involves chemical reactions (e.g., denaturation of proteins, caramelization of sugars) that form new substances, making it a chemical change. Dissolving sugar in water is a physical change because no new substance is formed (sugar can be recovered by evaporation). Breaking glass is a physical change (change in size/shape). Melting wax is a physical change (change of state).
Explanation:
Saline water (containing NaCl) increases the electrical conductivity of the water, accelerating the electrochemical process of rusting. This is why ships and coastal structures rust faster. Dry air and vacuum have no moisture; pure water without dissolved oxygen slows rusting.
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