Micelle: Formation, Structure, Soap Action & Sample Questions | Physical Chemistry PDF Download

Micelle Structure & Formation 

Let’s understand few terms:

• Hydrophilic end: ‘Hydro’ denotes water and ‘philic’ denotes fondness. The head, which is the polar or ionic part of the micelle, is affined to water. This forms the outer structure of the micelle.
• Hydrophobic end: ‘Hydro’ denotes water and ‘phobic’ denotes fear. The tail, which is the nonpolar end of the micelle, is water repulsive. It is not soluble in water and is attracted to dirt.
  When an amphiphilic molecule arranges itself in an aqueous solution, in a form that hydrophilic part remains outside and hydrophobic part forms the core, then a micelle is formed.
• Surfactant: This comes from two words- surface & active agent. It has the characteristic to decrease the surface tension between two liquids, gas & liquid or liquid & solid. Any detergent or foaming agent can be an example of surfactants.
• Critical Micelle Concentration: The concentration above which the surfactant forms micelles is known as critical micelle concentration. It is important because the surface tension changes dynamically below CMC.

Micelle Cleansing action of Soaps & Detergents 

We know that we cannot clean a dirty cloth only by using water. That is because water cannot dissolve oil or dirt. Hence we require a surfactant, like soap or detergent. The hydrophilic head of soap is attracted by water and the hydrophobic end is attracted to non-polar particles like dirt. This forms a micelle.
The outer surface of the micelle is charged. All the micelles formed in the solution have similar charges and they repel each other and are suspended in the water. When agitated, they remain suspended and you get squeaky clean clothes.

Points to Remember based on Micelle 

• Micelles are structures formed in an aqueous solution due to polar and nonpolar regions of the molecules present in the solution.
• Micelles have hydrophobic tails and hydrophilic heads.
• Formation of micelle due to a surfactant is the reason how soap cleansing works.

Sample Questions based on Micelle

OR Explain the sentence: The same substance can act both as colloids & crystalloids. (1 mark)
Q.4. Describe (i) Oil dispersed in water (O/W type) (ii) Water dispersed in oil (W/O type) (1 mark)
Q.5. Define Kraft temperature (1 mark)
Q.6. Explain the mechanism of cleansing action of soaps. (2 marks)