Question

Which one of the following is a cationic detergent?

• A. Cetyltrimethylammonium bromide
• B. Sodium dodecylbenzene sulphonate
• C. Dodecylbenzene sulphonic acid
• D. Dodecylbenzene

Hint:

Cetyltrimethylammonium bromide is a cationic detergent used in antiseptics and fabric softeners.

Answer 1

The Correct Option is A

Cationic detergents are surfactants that carry a positive charge on their hydrophilic end. They belong to the class of quaternary ammonium compounds, which are known for their bactericidal properties and are commonly used as fabric softeners and in disinfectants. Let us examine the options given to identify which is a cationic detergent:

1. Cetyltrimethylammonium bromide: This compound is a typical cationic detergent. It contains a quaternary ammonium ion in which the nitrogen atom carries a positive charge. This makes it hydrophilic, while the long alkyl chain (cetyl group) acts as the hydrophobic part, allowing it to function effectively as a surfactant.
2. Sodium dodecylbenzene sulphonate: This is an anionic detergent, as it contains a negative charge on the sulfonate group, making it hydrophilic. The sodium ion is merely a counterion.
3. Dodecylbenzene sulphonic acid: This is also an anionic compound, as it has a negative sulfonic acid group, which upon neutralization gives soaps or anionic detergents.
4. Dodecylbenzene: This is not a detergent; rather, it is a hydrocarbon without any ionic (hydrophilic) parts, making it neither cationic nor viable as a surfactant.

From the above analysis, it is clear that Cetyltrimethylammonium bromide is the only option that is a cationic detergent due to the presence of the positively charged quaternary ammonium ion.

Therefore, the correct answer is Cetyltrimethylammonium bromide.