Question

Among the following, the surfactant that will form micelles in aqueous solution at the lowest molar concentration at ambient conditions is:
A.\[{\text{C}}{{\text{H}}_3}{({\text{C}}{{\text{H}}_2})_{15}}{{\text{N}}^ + }{({\text{C}}{{\text{H}}_3})_3}{\text{B}}{{\text{r}}^ - }\]
B.\[{\text{C}}{{\text{H}}_3}{({\text{C}}{{\text{H}}_2})_{11}}{\text{OS}}{{\text{O}}_3}^ - {\text{N}}{{\text{a}}^ + }\]
C.\[{\text{C}}{{\text{H}}_3}{({\text{C}}{{\text{H}}_2})_6}{\text{CO}}{{\text{O}}^ - }{\text{N}}{{\text{a}}^ + }\]
D.\[{\text{C}}{{\text{H}}_3}{({\text{C}}{{\text{H}}_2})_{11}}{\text{N}}{{\text{a}}^ + }{({\text{C}}{{\text{H}}_3})_3}{\text{B}}{{\text{r}}^ - }\]

Answer 1

Hint: For the above question we need to have the knowledge of surfactant action. The bigger the molecular chain is the easier it will form micelles at lower molar concentration.

Complete step by step answer:
Surfactant is the compound that reduces the surface tension. They reduce surface tension between two liquids, between a liquid and a gas or between a solid and a liquid. The word surfactant is a combination of surface active agents. They are generally organic compounds, salts of long chains of fatty acids. It has two ends, one is hydrophilic and one is hydrophobic. Hydrophilic is water loving or water soluble components and other is hydrophobic that is water repellent or water insoluble.
Surfactants form aggregate molecules such as micelles. The hydrophobic end makes most of the micelles. The critical molar concentration is the concentration of surfactant molecules present in the bulk of the solution. The micelles start forming above this critical molar concentration.
It depends on chain length, the higher numbers of carbons are there in the chains the lower will be the critical molar concentration. As we can see that the highest number of carbons are in \[{\text{C}}{{\text{H}}_3}{({\text{C}}{{\text{H}}_2})_{15}}{{\text{N}}^ + }{({\text{C}}{{\text{H}}_3})_3}{\text{B}}{{\text{r}}^ - }\].

Hence the correct option is option A.

Note:
Surface tension is the tendency of liquid to have the minimum possible area. As the surface area of the sphere is least that is why the surface of liquid is curved. Surfactants play very important in various fields such as cleaning, foaming, emulsifying and dispersing agents. They are also used in firefighting and pipelines.