Question

Question = Why does micelles formation take place when soap is added to the water ? ​

Answer 1

The molecules of soap are such that in which two ends have different properties,one is hydrophilic i.e.it dissolves in water while the other end is hydrophobic i.e. it dissolve in hydrocarbon. When soap is at the surface water and the hydrophobic tail of the soap will not be soluble in water and the soap will align along the surface of water with 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 water.This is achieved by forming clusters of molecule in which hydrophobic ends are in the interior of the cluster and ionic ends on the surface of cluster.This formation is called as Micelle.

Ethanol is a non-polar solvent in it there is no attraction for hydrophilic part hence in ethanol the Micelle will not form.

Answer 2

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Micelle formation takes place when soap is added to water. Soap is made up of two parts,

i) Hydrophilic part, which is water loving and.

ii) Hydrophobic part, water repulsing part. Also, a soap has a long chain of an alkyl group, which is hydrophobic and $\sf -SO_{4}^{-} Na^{+},}$ which is hydrophilic. Now $\sf -SO_{4}^{-} Na^{+},}$ is the acid head of the soap and is capable of ionic reactions and thus dissolves in water whereas the carbon chain dissolves in oil.

When soap is added to water, the soap molecules align themselves in a spherical fashion as ionic ends face away from each other owing to the repulsive forces of the negative charge while the hydrophobic part of the soap is in the interior away from water. This spherical formation by soap in water is called micelle formation.

Organic additives such as alcohols would not be expected to partition into the interior of the micelle when present in small amounts.  The energy requirement for bringing the hydrophobic tail into solution may decrease, leading to an increase in micelle concentration. Conversely, adding alcohol will result in a reduction in the dielectric constant of the solvent mixture such effect would tend to decrease the critical micelle concentration of ionic surfactants as a result of their lower solubility and reduced repulsion between adjacent head groups at the micelle surface. This will in turn make alkyl group of soap micelle soluble as they will not able to form chains. Similarly in ethanol micelle formation doesn’t take place.