Why is controlled heating necessary to make plaster of Paris from gypsum?
Answer and explanation
Correct answer: Because only part of the water of crystallisation must be removed
The governing concept is controlled dehydration of a hydrated salt. Gypsum is calcium sulphate dihydrate, CaSO4·2H2O. Gentle heating removes part of its water of crystallisation and forms plaster of Paris, CaSO4·½H2O. If heating is excessive, more water may be driven off and the desired setting properties can be lost. Therefore option B is correct; calcium, chlorine, and sodium are not being removed or formed.
Frequently asked questions
What is the correct answer to this question?
Because only part of the water of crystallisation must be removed
Why is this the correct answer?
The governing concept is controlled dehydration of a hydrated salt. Gypsum is calcium sulphate dihydrate, CaSO4·2H2O. Gentle heating removes part of its water of crystallisation and forms plaster of Paris, CaSO4·½H2O. If heating is excessive, more water may be driven off and the desired setting properties can be lost. Therefore option B is correct; calcium, chlorine, and sodium are not being removed or formed.
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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