If soap does not lather in hard water but starts lathering after adding washing soda, what is the correct reason?
Answer and explanation
Correct answer: Hardness-causing ions are removed
Hard water contains Ca²⁺ and Mg²⁺ ions. These ions react with soap anions to form insoluble calcium or magnesium soaps, commonly called scum, so lather is not produced readily. Washing soda supplies carbonate ions that precipitate the hardness-causing ions as carbonates. Once those ions are removed, soap can form lather normally. Therefore, option A is correct.
Frequently asked questions
What is the correct answer to this question?
Hardness-causing ions are removed
Why is this the correct answer?
Hard water contains Ca²⁺ and Mg²⁺ ions. These ions react with soap anions to form insoluble calcium or magnesium soaps, commonly called scum, so lather is not produced readily. Washing soda supplies carbonate ions that precipitate the hardness-causing ions as carbonates. Once those ions are removed, soap can form lather normally. Therefore, option A 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.
