Both soap and detergent are some type of salt. Why does soap not form lather in hard water?

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Soap reacts with water molecules.

Soap reacts with the calcium and magnesium salts present in hard water.

Impurities present in hard water deactivate the soaps.

All of these

answer is B.

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Detailed Solution

Concept- Soaps are sodium or potassium salts of long chain fatty acids while detergents are ammonium or sulphate salts of fatty acids. Soaps have weak cleansing action while detergents have strong cleansing action. Soaps can’t be used in hard water but detergents can be used in hard and soft water. Soaps are biodegradable, but detergents are not.
Soaps above a particular concentration called ‘micelle concentration’ form micelles (a spherical formation) in water. In the two ends of fatty acids, one acts as lyophilic (water-loving) and another one as lyophobic (water-repelling). In micelles, this lyophilic end is headed outwards and lyophobic end is headed inside. Dirt having an oily nature gets enclosed inside micelle. And on washing with water, the dirt is removed.
Hard water contains salts of calcium and magnesium. Soaps when treated in hard water, forms complexes with them and precipitate out. Thus, it does not form lather and does not have cleansing.
Hence, the correct option is (2).

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