Question

Under ambient conditions, which among the following surfactants will form a micelle in aqueous solution at lowest molar concentration?

• A. $C{H}_3\left(C{H}_2{)}_{11}\stackrel{\oplus }{N}\right(C{H}_3{)}_{3}B{r}^{-}$
• B. $C{H}_3-(C{H}_2{)}_{13}-OS{O}_3^{⊝}N{a}^{+}$
• C. $C{H}_3\left(C{H}_2{)}_{15}\stackrel{\oplus }{N}\right(C{H}_3{)}_{3}B\stackrel{⊝}{r}$
• D. $C{H}_3-(C{H}_2{)}_8-CO{O}^{⊝}N{a}^{+}$

Answer 1

Answer: (C)

$C{H}_3\left(C{H}_2{)}_{15}\stackrel{\oplus }{N}\right(C{H}_3{)}_{3}B\stackrel{⊝}{r}$

Micelles may be defined to be aggregates of long-chain diphilic surfactant molecules or ions formed spontaneously in their solutions at a definite concentration.

Micelles formed by the cooperative binding of monomers to one another at concentrations exceeding a rather narrow region called the critical micellization concentration (CMC).

Greater is the size of the hydrophobic chain, less will be its solubility in water and its chances to form micelle will be more.

Thus, $C{H}_3\left(C{H}_2{)}_{15}\stackrel{\oplus }{N}\right(C{H}_3{)}_3\stackrel{\ominus }{B}r$ will form a micelle in aqueous solution as it has the longest hydrophobic chain.