Question

Which one of the following methods is most suitable for preparing deionized water ?

• A. Clark's method
• B. Synthetic resin method
• C. Calgon's method
• D. Permutit method

Hint:

Only the ion-exchange resin (synthetic resin) method can remove both anions and cations entirely, making it the standard for high-purity laboratory water.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Hard water contains dissolved salts, mainly calcium and magnesium ions. While some methods only "soften" water by removing these specific ions, others can remove all dissolved ions to produce deionized or demineralized water.
Step 2: Detailed Explanation:
1. Clark's method: Used for removing temporary hardness by adding lime (\(Ca(OH)_2\)). It does not remove all ions.
2. Calgon's method: Uses sodium hexametaphosphate to sequester \(Ca^{2+}\) and \(Mg^{2+}\) ions. It softens water but doesn't deionize it.
3. Permutit method (Zeolite): Exchanges \(Na^+\) for \(Ca^{2+}\) and \(Mg^{2+}\). The resulting water contains \(Na^+\) ions.
4. Synthetic resin method: This involves cation exchange resins (which replace cations with \(H^+\)) and anion exchange resins (which replace anions with \(OH^-\)). The \(H^+\) and \(OH^-\) combine to form water. This process removes all dissolved mineral salts, resulting in pure deionized water.
Step 3: Final Answer:
The synthetic resin method is most suitable for preparing deionized water.