Why is Plaster of Paris formed when gypsum is heated carefully?
Answer and explanation
Correct answer: Part of the water of crystallisation is removed
Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. Careful heating removes part of its water of crystallisation and produces Plaster of Paris, calcium sulphate hemihydrate: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O. Limited heating is important; excessive heating can remove more water and reduce the desired setting property. Therefore A is correct, while calcium does not burn and gypsum does not become sulphur or common salt.
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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 sulphate dihydrate, CaSO₄·2H₂O. Careful heating removes part of its water of crystallisation and produces Plaster of Paris, calcium sulphate hemihydrate: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O. Limited heating is important; excessive heating can remove more water and reduce the desired setting property. Therefore A is correct, while calcium does not burn and gypsum does not become sulphur or common salt.
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.
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