Which substance is used to soften hard water?
Answer and explanation
Correct answer: Washing soda
Hard water contains dissolved calcium and magnesium salts. Washing soda, Na₂CO₃·10H₂O, supplies carbonate ions that react with soluble calcium or magnesium ions to form insoluble carbonates, which can be removed. This decreases the ions responsible for hardness, so option A is correct. Vinegar and lemon juice are acids, while common salt does not generally precipitate the hardness-causing ions and therefore is not the standard softening substance.
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 salts. Washing soda, Na₂CO₃·10H₂O, supplies carbonate ions that react with soluble calcium or magnesium ions to form insoluble carbonates, which can be removed. This decreases the ions responsible for hardness, so option A is correct. Vinegar and lemon juice are acids, while common salt does not generally precipitate the hardness-causing ions and therefore is not the standard softening substance.
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.
