Why is plaster of Paris formed when gypsum is heated in a controlled way?
Answer and explanation
Correct answer: Some water of crystallisation is removed from gypsum
The governing concept is controlled thermal dehydration of a hydrated salt. Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. On careful heating, it loses one and a half molecules of water per formula unit and changes into calcium sulphate hemihydrate, CaSO₄·½H₂O, which is plaster of Paris. Therefore, option A is correct; no metal formation or chlorine release is involved.
Frequently asked questions
What is the correct answer to this question?
Some water of crystallisation is removed from gypsum
Why is this the correct answer?
The governing concept is controlled thermal dehydration of a hydrated salt. Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. On careful heating, it loses one and a half molecules of water per formula unit and changes into calcium sulphate hemihydrate, CaSO₄·½H₂O, which is plaster of Paris. Therefore, option A is correct; no metal formation or chlorine release is involved.
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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