Question

The exhausted anion-exchange resin is regenerated with

• A. dilute $NaOH$ solution
• B. dilute $NaCl$ solution
• C. dilute $HCl$ solution
• D. dilute $Na_{2}SO_{4}$ solution

Hint:

Cation Resins use Acids ($H^{+}$); Anion Resins use Bases ($OH^{-}$).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Ion exchange resins are used for water demineralization. Anion-exchange resins pick up negative ions (like $Cl^-, SO_4^{2-}$) and release $OH^-$. When "exhausted," they are saturated with these impurity anions.
Step 2: Key Formula or Approach:
To regenerate, you must provide a high concentration of the original ion ($OH^-$) to drive the equilibrium backward.
Step 3: Detailed Explanation:
An exhausted anion resin ($R-Cl$) needs to be converted back to its basic form ($R-OH$). This is achieved by washing it with a dilute NaOH solution. The high concentration of $OH^-$ displaces the chloride ions: \[ R-Cl + NaOH \rightarrow R-OH + NaCl \] Conversely, a cation-exchange resin is regenerated with dilute $HCl$ or $H_2SO_4$.
Step 4: Final Answer:
Dilute NaOH solution is used for regeneration.