Question

Which of the following forms cationic micelles above a certain concentration?
A. Sodium dodecyl sulphate
B. Sodium acetate
C. Urea
D. Cetyl trimethyl ammonium bromide

Answer 1

Hint: In aqueous solutions, molecules having both a charged group and an uncharged group that forms aggregates are called micelles. In a micelle, the charged group forms an outer shell and an uncharged group is present inside it. In cationic micelle, the charge present is positive. Divide the given compounds into cations and anions and see which forms cationic micelles above a certain concentration. And quaternary ammonium compounds form cationic surfactants. Use this info to solve the question.

Complete step by step answer:
We have to first know what micelles are.
Micelles are basically a loosely bound assembly of several ions of the surfactant which leads to the formation of the colloidal suspension.
Micelles are formed by arranging amphiphilic molecules together. The hydrophilic head is surrounded by solvent and the hydrophilic tail is in the centre of the micelle.
First, we have sodium dodecyl sulphate. It forms a hydrocarbon core and hydrophilic ionic surface when dissolved in water. It is an anionic surfactant.
Second, we have Urea. Urea does not form micelle but affects the concentration of micelle.
Third, we have sodium acetate. It acts as an electrolyte, not as a micelle.
Fourth we have Cetyl trimethyl ammonium bromide. It is also known as cetrimonium bromide and it forms a cationic micelle by forming ammonium cation.

Therefore, the correct option is Option D..

Note:
Micelle formation is important for the absorption of fat-soluble vitamins in the human body. When surfactants are present above the critical micelle concentrations, they act as emulsifiers thus allowing a compound to dissolve in the solute in which it was insoluble before.