Hardness of water can be removed by boiling if it is due to
- Acalcium sulphate
- Bmagnesium sulphate
- Ccalcium chloride
- Dcalcium bicarbonateCorrect
Solution
Concept
Boiling removes temporary hardness caused by bicarbonates.
Formula
Ca(HCO3)2 → CaCO3 ↓ + H2O + CO2
Step-by-step solution
1. Temporary hardness is due to bicarbonates of calcium and magnesium. 2. On boiling, the bicarbonate breaks down. 3. Insoluble CaCO3 settles out. 4. Sulphates and chlorides cause permanent hardness and stay in water.
Explanation
Calcium bicarbonate gives temporary hardness. When heated, it forms insoluble calcium carbonate which settles out. Sulphates and chlorides are not removed by boiling.
Why the other options are wrong
A, B and C are sulphates or chlorides. They cause permanent hardness and need lime-soda or zeolite treatment.
Shortcut
Bicarbonate = temporary = boiling removes it.
Common mistake
Thinking boiling removes all hardness.
Correct answer: D) calcium bicarbonate