Which of the following are present in a higher amount in hard water?
- ASodium and manganese
- BCalcium and sodium
- CSodium and magnesium
- DCalcium and magnesium
Show answer and explanation
Correct answer: (d) Calcium and magnesium
Explanation
Water is hard when it contains dissolved salts of calcium (Ca²⁺) and magnesium (Mg²⁺). These ions react with soap to form an insoluble scum, so the soap does not lather well.
- Temporary hardness comes from calcium and magnesium bicarbonates and can be removed by boiling.
- Permanent hardness comes from their chlorides and sulphates, removed by washing soda or ion exchange.
Sodium salts do not cause hardness. Water softeners actually replace calcium and magnesium ions with sodium ions.