Which substance is useful in softening hard water?
Answer and explanation
Correct answer: Washing soda
Hard water contains dissolved calcium and magnesium ions, which can interfere with soap and form deposits. Washing soda, sodium carbonate (Na₂CO₃), supplies carbonate ions that react with Ca²⁺ and Mg²⁺ to form insoluble carbonates. These precipitates can be removed, lowering the concentration of hardness-causing ions and softening the water. Baking soda, vinegar, and common salt do not perform this standard softening action, so option B is correct.
Frequently asked questions
What is the correct answer to this question?
Washing soda
Why is this the correct answer?
Hard water contains dissolved calcium and magnesium ions, which can interfere with soap and form deposits. Washing soda, sodium carbonate (Na₂CO₃), supplies carbonate ions that react with Ca²⁺ and Mg²⁺ to form insoluble carbonates. These precipitates can be removed, lowering the concentration of hardness-causing ions and softening the water. Baking soda, vinegar, and common salt do not perform this standard softening action, so option B is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
