JEE Advance - Chemistry (2008 - Paper 2 Offline - No. 9)
Among the following, the surfactant that will form micelles in aqueous solution at the lowest molar concentration at ambient condition is:
CH$$_3$$(CH$$_2$$)$$_{15}$$N$$^+$$(CH$$_3$$)$$_3$$Br$$^-$$
CH$$_3$$(CH$$_2$$)$$_{11}$$OSO$$_3^-$$Na$$^+$$
CH$$_3$$(CH$$_2$$)$$_6$$COO$$^-$$Na$$^+$$
CH$$_3$$(CH$$_2$$)$$_{11}$$N$$^+$$(CH$$_3$$)$$_3$$Br$$^-$$
Explanation
The surfactant CH$$_3$$(CH$$_2$$)$$_{15}$$N$$^+$$(CH$$_3$$)$$_3$$Br$$^-$$ forms micelles at lowest concentration.
Critical concentration for micelle formation decreases as the molecular weight of hydrocarbon chain of surfactant grows because its true solubility diminishes and the tendency of surfactant molecule to associate increases. The molecular weight is maximum in case of CH$$_3$$(CH$$_2$$)$$_{15}$$N$$^+$$(CH$$_3$$)$$_3$$Br$$^-$$.
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