JEE Main 2021 · 17 March · evening · Single correct · +4 / −1
The functional groups that are responsible for the ion-exchange property of cation and anion exchange resins, respectively, are :
- (a) -SO₃H and -NH₂
- (b) -NH₂ and COOH
- (c) -NH₂ and -SO₃H
- (d) -SO₃H and -COOH
Answer and solution
Answer (a) -SO₃H and -NH₂
Solution
Chemistry ma’am · 3 steps
Acid group swaps cations, basic group swaps anions: so -SO₃H first, then -NH₂.
- Cation exchange resin. This resin must give up a cation and take in another, such as Ca²⁺ or Mg²⁺ from hard water. So it needs an acidic group that can release H⁺. The strongly acidic sulphonic acid group does this: R-SO₃H + Na⁺ → R-SO₃Na + H⁺.
- Anion exchange resin. This resin must swap anions such as Cl⁻ or SO₄²⁻. So it needs a basic group. An amino group -NH₂ picks up water to become -NH₃⁺ OH⁻, and that OH⁻ is exchanged: R-NH₃⁺OH⁻ + Cl⁻ → R-NH₃⁺Cl⁻ + OH⁻.
Group Nature Ion it exchanges Resin type -SO₃H acidic H⁺ for cations cation exchanger -COOH acidic (weaker) H⁺ for cations cation exchanger -NH₂ basic OH⁻ for anions anion exchanger - So. In the order cation, then anion, the pair is -SO₃H and -NH₂, which is option (a).
The idea to keep. Match the charge: an acidic group releases H⁺, so it exchanges cations. A basic amino group holds OH⁻, so it exchanges anions.
Answer from the NTA final answer key. Solution by PrepWiser.