Hard water can be softened by ion exchange method. The resin exchanges ________ for Ca²⁺ and Mg²⁺ ions.
A. OH⁻
B. H⁺
C. Na⁺
D. Cl⁻
Answer: Option C
Solution (By JKExamLibrary)
Cation exchange resins contain Na⁺ ions which are replaced by Ca²⁺/Mg²⁺, softening the water. Anion exchange can also be used for deionization. Washing soda precipitates Ca/Mg.
Explanation:
Permanent hardness is due to CaCl₂, CaSO₄, MgCl₂, MgSO₄. These do not precipitate on boiling. Temporary hardness (bicarbonates) is removed by boiling. Both can be removed by ion exchange or washing soda.
Explanation:
Sodium reacts vigorously with moisture and oxygen in air, so it is stored under kerosene to prevent contact. Potassium, lithium are similarly stored. Iron, zinc, copper do not require such storage.
Explanation:
Thermite: Fe₂O₃ + 2Al → 2Fe + Al₂O₃. Aluminium powder reduces iron oxide, producing molten iron for welding. Al is chosen due to its high reactivity and exothermic reaction.
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