Hard water does not lather well with soap because it forms:
A. Soluble sodium salts
B. Foam
C. Alkaline solution
D. Insoluble calcium and magnesium soap (scum)
Answer: Option D
Solution (By JKExamLibrary)
Soap (sodium/potassium salts of long-chain fatty acids) reacts with Ca²⁺ and Mg²⁺ ions in hard water to form insoluble calcium/magnesium salts (scum), which precipitates and does not lather. This wastes soap. Reaction: 2RCOONa + Ca²⁺ → (RCOO)₂Ca↓ + 2Na⁺. Detergents do not form scum because their calcium salts are soluble. Hardness is measured in ppm of CaCO₃.
Explanation:
Silver has the highest thermal conductivity, followed by copper. It's also the best electrical conductor. Copper is more commonly used due to cost.
Explanation:
Aluminium oxide: Al³⁺ and O²⁻. To balance charges, 2 Al³⁺ (total +6) combine with 3 O²⁻ (total -6). Thus valency of Al is 3. It loses three electrons. Formula determined by criss-cross method.
Explanation:
Manganese is extracted by the aluminothermic process (Goldschmidt thermite process) where Mn₃O₄ is reduced by aluminium: 3Mn₃O₄ + 8Al → 9Mn + 4Al₂O₃. This works for metals with less reactivity than Al but not too reactive. Sodium is extracted by electrolysis. Iron is extracted by smelting with coke. Zinc by carbon reduction/electrolysis.
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