JEE Main 2022 · 26 June · evening · Single correct · +4 / −1
Which of the following is NOT an example of synthetic detergent?
- (a)
- (b) CH₃ - (CH₂)₁₆ - COO - Na +
- (c) [CH₃-(CH₂)₁₅-N(|(CH₃))-CH₃]⁺ Br⁻
- (d) CH₃(CH₂)₁₆COO(CH₂CH₂O)ₙCH₂CH₂OH
Answer and solution
Answer (b) CH₃ - (CH₂)₁₆ - COO - Na +
Solution
Chemistry ma’am · 2 steps
Look at the head group: a -COO⁻Na⁺ on a long fatty chain means soap, not a synthetic detergent.
- Soap versus detergent. A soap is the sodium or potassium salt of a long-chain fatty acid, so its polar head is -COO⁻. A synthetic detergent has a different head: a sulphonate or sulphate (anionic), a quaternary ammonium ion (cationic), or a neutral polyether chain (non-ionic).
Option Polar head Name Type (a) -SO₃⁻Na⁺ on a benzene ring sodium dodecylbenzenesulphonate anionic detergent (b) -COO⁻Na⁺ sodium stearate soap (c) -N⁺(CH₃)₃ with Br⁻ cetyltrimethylammonium bromide cationic detergent (d) -COO(CH₂CH₂O)ₙCH₂CH₂OH, an ester polyethylene glycol stearate non-ionic detergent - So. Only (b), sodium stearate, is a carboxylate salt of a fatty acid. It is an ordinary soap, so it is not a synthetic detergent.
The idea to keep. Classify by the polar head. -COO⁻Na⁺ is soap. -SO₃⁻ or -OSO₃⁻ is anionic, -N⁺R₃ is cationic, and a polyether chain with no charge is non-ionic detergent.
Answer from the NTA final answer key. Solution by PrepWiser.