Water treatment (permanent hardness): Which method cannot remove permanent hardness due to Ca/Mg chlorides/sulfates? Identify the technique ineffective against non-bicarbonate hardness. Choose the correct option.

Water treatment (permanent hardness): Which method <em>cannot</em> remove <strong>permanent hardness</strong> due to Ca/Mg chlorides/sulfates? Identify the technique ineffective against non-bicarbonate hardness. Choose the correct option.

Difficulty: Easy

Adding sodium carbonate (washing soda)
Distillation
Adding caustic soda (NaOH)
Boiling

Correct Answer: Boiling

Explanation:

Given data

Permanent hardness arises from Ca/Mg chlorides and sulfates.

Concept/Approach
Boiling removes temporary hardness (bicarbonates) by decomposing HCO₃⁻ to CO₃²⁻/CO₂. It does not remove chlorides/sulfates. Washing soda (Na₂CO₃) precipitates CaCO₃; distillation removes all salts; NaOH can precipitate Mg(OH)₂ and assist softening in appropriate processes.

Final Answer
Boiling

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