Name: Uses of Adsorption
Uploaded: 2019-07-19
Duration: 2 min 48 s
Description: Do you know how gas masks work? How does a perfume scent stick to us for long hours? It's all possible due to adsorption. Isn't it interesting? Learn more.

Question

Explain the formation of micelles with a neat sketch.

Accepted Answer

Let us take the example of soap solution. Soap is sodium or potassium salt of a higher fatty acid and may be represented as ${RCOO}^{-} {Na}^{+}$ (e.g., sodium stearate ${CH}_{3} {({CH}_{2})}_{16} {COO}^{-} {Na}^{+}$ , which Is a major component of many bar soaps). When dissolved in water, It dissociates into ${RCOO}^{-}$ and ${Na}^{+}$ ions. The ${RCOO}^{-}$ Ions, however, consist of two parts: a long hydrocarbon chain $R$ (also called non-polar ‘tail’) which Is hydrophobic (water repelling), and a polar group ${COO}^{-}$ (also called polar-ionic ‘head’), which Is hydrophilic (water loving).

The ${RCOO}^{-}$ ions are, therefore, present on the surface with their ${COO}^{-}$ groups in water and the hydrocarbon chains $(R)$ staying away from it and remain at the surface. But at critical micelle concentration, the ${COO}^{-}$ ions are pulled into the bulk of the solution and are aggregated to form a spherical shape with their hydrocarbon chains pointing towards the centre of the sphere with ${COO}^{-}$ part remaining outward on the surface of the sphere. The aggregate thus formed is known as ‘ionic micelle'. These micelles may contain as many as 100 simple molecules.

Explain the formation of micelles with a neat sketch.

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