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Cetyl trimethyl ammonium bromide, [C16H33(CH3)3N+Br−], is an example of a cationic surfactant that forms micelles. Which of the following statements is accurate?

1. The micelle consists of a polar head and a non-polar tail.
2. Adding an electrolyte neutralizes the charge on colloidal particles, leading to coagulation.
3. The coagulating ability of ions on oppositely charged colloidal particles increases with their valency, and the order of coagulating power is Al3+ > Ba2+ > Na+.
4. Micelle formation begins at the critical micelle concentration (CMC), and above this concentration, surfactants can act as emulsifiers to dissolve substances like oil or dirt that are otherwise insoluble in the solvent.

Correct answer: Micelle formation begins at the critical micelle concentration (CMC), and above this concentration, surfactants can act as emulsifiers to dissolve substances like oil or dirt that are otherwise insoluble in the solvent.

Solution

Option D correctly defines the critical micelle concentration (CMC) and its role in micelle formation and emulsification. The other options are unrelated to the specific concept of CMC.

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