Question

An example for cationic detergent is:
(A)- NaLS
(B)- CTAB
(C)- Trimethyl phosphate
(D)- All

Answer 1

Hint: The electrical charge on the larger portion of the detergent molecule will determine its ionic nature to be cationic (positively charged), anionic (negatively charged) and the neutral is non-ionic.

Complete answer:
Detergents are surface-active agents. This is because of their possible interaction with the water molecules as well as the solid particles, in presence of the hydrophobic and the hydrophilic part in its molecule.
A detergent is a sodium salt of long chain of alkyl benzene sulphonates or the alkyl hydrogen sulphate. The long hydrocarbon chain is the hydrophobic part which is insoluble in water but can dissolve oil and grease. Whereas the sodium salt, which is the ionic, is the hydrophilic part and interacts with the water molecule.
So, due to the electrical charge on the ionic part, the detergents can be classified into:
- Cationic detergents in which the large portion consisting of the hydrophobic long hydrocarbon chain along with the nitrogen atom has a positive charge. It is usually the quaternary ammonium salts with the chlorides, bromides or acetates carrying the negative charge. So, the CTAB, that is, cetyltrimethylammonium bromide, $\left[ {{H}_{3}}C-{{(C{{H}_{2}})}_{15}}-\overset{\oplus }{\mathop{N}}\,-{{(C{{H}_{3}})}_{3}} \right]B{{r}^{-}}$ is a cationic detergent.
- Anionic detergents have a long hydrocarbon chain with its soluble end with the negative charge. Like in the sodium salt of long-chain sulfonated alcohols or hydrocarbons. So, the NaLS, that is, sodium lauryl sulphate, ${{C}_{11}}{{H}_{23}}C{{H}_{2}}OSO_{3}^{-}N{{a}^{+}}$ is an anionic detergent.
- Non-ionic detergents do not consist of ions. The trimethyl phosphate is an example of it.
Therefore, the example for cationic detergent is option (B)- CTAB (cetyltrimethylammonium bromide).

Note:
Due to the ionic parts of the detergent, it is used for the cleansing action as it lowers the surface tension of the water surface and easily binds with the dirt or oil.