Why does soap produce less foam in hard water?
Answer and explanation
Correct answer: Calcium and magnesium ions form insoluble scum with soap
The governing concept is the reaction of soap with hardness-producing ions. Hard water contains dissolved calcium (Ca2+) and magnesium (Mg2+) ions. These ions react with the fatty-acid anions of soap to form insoluble calcium or magnesium salts, commonly called scum. Because part of the soap is consumed in this precipitate, less soap remains available to form lather, so foam decreases. Hence option A is correct.
Frequently asked questions
What is the correct answer to this question?
Calcium and magnesium ions form insoluble scum with soap
Why is this the correct answer?
The governing concept is the reaction of soap with hardness-producing ions. Hard water contains dissolved calcium (Ca2+) and magnesium (Mg2+) ions. These ions react with the fatty-acid anions of soap to form insoluble calcium or magnesium salts, commonly called scum. Because part of the soap is consumed in this precipitate, less soap remains available to form lather, so foam decreases. Hence option A is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Carbon and its Compounds. Topic: Soaps and detergents.
