Which one of the following statements about the cleansing action of so

Which one of the following statements about the cleansing action of soap is not true ?

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The oil and dirt gets collected in the centre of the micelle.

Soap micelles scatter light.

Soaps are ammonium salts of long chain carboxylic acids.

Soap forms insoluble precipitates with the calcium and magnesium ions in hard water.

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC NDA-1 – 2021

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Statement C is not true. Soaps are typically sodium or potassium salts of long chain carboxylic acids. Ammonium salts of long chain carboxylic acids are commonly used as detergents, which have similar cleansing properties but differ in their chemical composition and behaviour in hard water.

Soaps function through the formation of micelles, aggregates of soap molecules in water, where the hydrophobic tails face inwards, dissolving oils and dirt, and the hydrophilic heads face outwards, interacting with water. Micelles are large enough to scatter light, a phenomenon known as the Tyndall effect. Soaps react with calcium and magnesium ions present in hard water to form insoluble precipitates called scum, which reduces their effectiveness.

Detergents, unlike soaps, do not form insoluble precipitates with calcium and magnesium ions in hard water, making them more effective for washing in hard water. The general formula for a soap molecule is RCOO⁻Na⁺ or RCOO⁻K⁺, where R is a long alkyl chain.

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