Question

Sodium stearate $C{H}_3(C{H}_2{)}_{16}CO{O}^{–}N{a}^{+}$ is an anionic surfactant which forms micelles in oil. Choose the correct statement for it from the following :

• A. It forms non–spherical micelles with $C{H}_3(C{H}_2{)}_{16}-$group pointing towards the centre.
• B. It forms spherical micelles with $C{H}_3(C{H}_2{)}_{16}-$ group pointing outwards on the surface of sphere
• C. It forms non–spherical micelles with $–COO–$ group pointing outwards on the surface
• D. It forms spherical micelles with $C{H}_3(C{H}_2{)}_{16}-$ group pointing towards the centre of sphere.

Answer 1

The correct option is D It forms spherical micelles with $C{H}_3(C{H}_2{)}_{16}-$ group pointing towards the centre of sphere.

The $RCO{O}^{-}$ ion consists of two parts :
long hydrocarbon chain (also called non – polar tail) which is hydrophobic (water repelling ) and a polar group $CO{O}^{-}$ (polar head) which is hydrophilic (water loving )
At higher concentrations(CMC) $RCO{O}^{-}$ ions form an aggregate of spherical shape with the hydrocarbon chains pointing towards the centre and the $CO{O}^{-}$ part facing outward on the surface of the sphere. This aggregate is called ionic micelle.
Option (a) is correct