Gypsum forms plaster of Paris on controlled heating. What is the main change?
Answer and explanation
Correct answer: Part of the water of crystallisation is removed
Gypsum is calcium sulfate dihydrate, CaSO₄·2H₂O. On controlled heating, it loses one and a half molecules of water of crystallisation and forms calcium sulfate hemihydrate, CaSO₄·½H₂O, known as plaster of Paris: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O. Thus A is correct. The calcium remains in the compound, sulphur does not become a gas, and water is removed rather than increased.
Frequently asked questions
What is the correct answer to this question?
Part of the water of crystallisation is removed
Why is this the correct answer?
Gypsum is calcium sulfate dihydrate, CaSO₄·2H₂O. On controlled heating, it loses one and a half molecules of water of crystallisation and forms calcium sulfate hemihydrate, CaSO₄·½H₂O, known as plaster of Paris: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O. Thus A is correct. The calcium remains in the compound, sulphur does not become a gas, and water is removed rather than increased.
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.
