Why can excessive heating of gypsum reduce the quality of plaster of Paris?
Answer and explanation
Correct answer: Excess water may be removed and the useful hemihydrate form may be spoiled
Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. Controlled heating removes part of its water of crystallisation and produces plaster of Paris, calcium sulphate hemihydrate, CaSO₄·½H₂O. If heating is excessive, more water can be removed and anhydrous calcium sulphate may form. That material does not hydrate and set as effectively, so the plaster quality falls. Hence option A is correct.
Frequently asked questions
What is the correct answer to this question?
Excess water may be removed and the useful hemihydrate form may be spoiled
Why is this the correct answer?
Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. Controlled heating removes part of its water of crystallisation and produces plaster of Paris, calcium sulphate hemihydrate, CaSO₄·½H₂O. If heating is excessive, more water can be removed and anhydrous calcium sulphate may form. That material does not hydrate and set as effectively, so the plaster quality falls. Hence option A is correct.
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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