Question

The type of functional group associated with cation exchange resin is

• A. -OH
• B. -$SO_{3}H$
• C. - $NH_{2}$
• D. -CHO

Hint:

Cation = Acidic group (contains H to swap). Anion = Basic group (contains OH or Amine to swap).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Ion-exchange resins are insoluble polymers that can exchange specific ions within a solution. Cation exchange resins must possess acidic functional groups that can release $H^+$ ions in exchange for other cations (like $Ca^{2+}$ or $Mg^{2+}$).
Step 2: Key Formula or Approach:
* Cation Exchange Resins: Contain acidic groups like sulphonic acid ($-SO_3H$) or carboxylic acid ($-COOH$). * Anion Exchange Resins: Contain basic groups like quaternary ammonium or amino groups ($-NH_2, -OH$).
Step 3: Detailed Explanation:
Cation resins are essentially giant organic molecules with fixed negative charges and mobile positive ions. The sulphonic acid group ($-SO_3H$) is a strong acid group commonly used in these resins. When hard water passes through, the $H^+$ ions from the $-SO_3H$ group are replaced by the cations present in the water: \[ 2R-SO_3H + Ca^{2+} \rightarrow (R-SO_3)_2Ca + 2H^+ \]
Step 4: Final Answer:
The functional group associated with cation exchange resin is -SO₃H.