Which of the following water purification methods can remove dissolved salts? MCQ with Answer and Explanation

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Question #1

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Which catalyst is used in the decomposition of KClO₃ to prepare oxygen in the laboratory?

A. Pt

B. Fe₂O₃

C. V₂O₅

D. MnO₂

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Correct Answer: Option D

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Explanation:
Manganese dioxide (MnO₂) catalyzes the thermal decomposition of potassium chlorate: 2KClO₃ (heat, MnO₂) → 2KCl + 3O₂. Without MnO₂, decomposition requires higher temperature. MnO₂ is not consumed. Other catalysts can be used, but MnO₂ is standard in school labs. V₂O₅ is for SO₂ oxidation, Pt for various, Fe₂O₃ not typical. This is a simple preparation of oxygen.

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Question #2

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The process of concentrating an ore by taking advantage of the difference in density between the ore and the gangue is:

A. Hydraulic washing

B. Froth flotation

C. Magnetic separation

D. Leaching

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Correct Answer: Option A

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Explanation:
Hydraulic washing, also known as gravity separation, is based on the difference in specific gravities (densities) of the metallic ore and the associated impurities (gangue). The powdered ore is washed with a running stream of water; the lighter impurities are carried away, leaving the heavier ore particles behind.

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Question #3

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Which of the following methods is used to obtain pure copper from impure copper?

A. Roasting

B. Calcination

C. Electrolytic refining

D. Smelting

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Correct Answer: Option C

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Explanation:
In electrolytic refining, impure copper is the anode, pure copper is the cathode, and CuSO₄ acidified with H₂SO₄ is the electrolyte. Copper dissolves from anode and pure copper deposits on cathode. Smelting is reduction with coke.

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