Which salt is commonly used to remove permanent hardness of water?
Answer and explanation
Correct answer: Na₂CO₃·10H₂O
Sodium carbonate decahydrate, Na₂CO₃·10H₂O, is washing soda. It removes permanent hardness by supplying CO₃²⁻ ions, which react with dissolved Ca²⁺ and Mg²⁺ ions to form insoluble carbonates that can be separated. Hence option A is correct. Calcium sulfate contributes to hardness, sodium bicarbonate is baking soda, and calcium oxychloride is bleaching powder, so the other choices do not perform this softening role.
Frequently asked questions
What is the correct answer to this question?
Na₂CO₃·10H₂O
Why is this the correct answer?
Sodium carbonate decahydrate, Na₂CO₃·10H₂O, is washing soda. It removes permanent hardness by supplying CO₃²⁻ ions, which react with dissolved Ca²⁺ and Mg²⁺ ions to form insoluble carbonates that can be separated. Hence option A is correct. Calcium sulfate contributes to hardness, sodium bicarbonate is baking soda, and calcium oxychloride is bleaching powder, so the other choices do not perform this softening role.
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.
