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Question
Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
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Solution
- Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is, it interacts with water, while the other end is hydrophobic, that is, it interacts with hydrocarbons.
- When soap is at the surface of water, the hydrophobic ‘tail’ of soap will not be soluble in water, and the soap will align along the surface of water with the ionic end in water and the hydrocarbon ‘tail’ protruding out of water.
- Inside water, these molecules have a unique orientation that keeps the hydrocarbon portion out of the water. Thus, clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle.
- Soap in the form of a micelle is able to clean, since the oily dirt will be collected in the centre of the micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion.
- Thus, the dirt suspended in the micelles is also easily rinsed away. The soap micelles are large enough to scatter light. Hence a soap solution appears cloudy.
- Since ethanol is not as polar as soap, so micelles will not be formed in other solvents such as ethanol.
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