Why is it necessary to heat gypsum only at controlled temperature?
Answer and explanation
Correct answer: Only part of water of crystallisation must be removed to form hemihydrate
Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. On controlled heating, it loses only part of its water of crystallisation and changes into calcium sulphate hemihydrate, CaSO₄·½H₂O, called plaster of Paris. If heating is excessive, the material may become anhydrous calcium sulphate and lose its useful setting property. Therefore, option A is correct; the other options describe unrelated changes.
Frequently asked questions
What is the correct answer to this question?
Only part of water of crystallisation must be removed to form hemihydrate
Why is this the correct answer?
Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. On controlled heating, it loses only part of its water of crystallisation and changes into calcium sulphate hemihydrate, CaSO₄·½H₂O, called plaster of Paris. If heating is excessive, the material may become anhydrous calcium sulphate and lose its useful setting property. Therefore, option A is correct; the other options describe unrelated changes.
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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