Question :What are soaps? Explain the mechanisms of the cleansing action of soap with the help of a labeled diagram.
(ii) Detergents are better than soaps. Justify.
The correct answer is -(i) Soaps are the sodium or potassium salts of long-chain fatty acids. They are formed by the reaction between an alkali (sodium hydroxide or potassium hydroxide) and a fat or oil. Soaps have a hydrophobic (water-repelling) tail and a hydrophilic (water-attracting) head. The hydrophobic tail attaches itself to the dirt and the hydrophilic head forms a micelle around the dirt particle. When the water is added, the micelle detaches from the surface and dirt particles are removed.
The cleansing action of soap can be explained by the following steps:
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The long hydrocarbon chain of the soap is nonpolar and tends to avoid water. When soap is added to water, the hydrophobic tail is attracted to the dirt, oil or grease, while the hydrophilic head is attracted to the water molecules.
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The hydrophobic tail surrounds the oil or grease droplet, forming a sphere called a micelle.
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The soap molecules on the outside of the micelle are attracted to the water molecules and are washed away with the water, carrying the micelle and dirt along with it.
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When the soap and water are rinsed off, the dirt, oil, and grease are removed from the surface.
(ii) Detergents are better than soaps in the following ways:
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Detergents work better in hard water than soaps as they do not react with the minerals in hard water to form insoluble compounds.
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Detergents can be used in both hot and cold water, whereas soaps work better in hot water.
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Detergents are more effective in removing grease and oil stains than soaps.
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Detergents are less likely to leave a residue on clothes, unlike soaps.
