Gypsum forms plaster of Paris when heated at about 373 K. Why may the desired product not be obtained on excessive heating?
Answer and explanation
Correct answer: Because too much water may be removed and anhydrous calcium sulphate may form
Gypsum is CaSO4·2H2O. Controlled heating removes only part of its water of crystallisation and produces plaster of Paris, CaSO4·1/2H2O. If heating is excessive, the remaining water can also be driven off, producing anhydrous calcium sulphate, CaSO4, commonly called dead-burnt plaster. This material does not rehydrate and set properly, so option A explains the loss of the desired product.
Frequently asked questions
What is the correct answer to this question?
Because too much water may be removed and anhydrous calcium sulphate may form
Why is this the correct answer?
Gypsum is CaSO4·2H2O. Controlled heating removes only part of its water of crystallisation and produces plaster of Paris, CaSO4·1/2H2O. If heating is excessive, the remaining water can also be driven off, producing anhydrous calcium sulphate, CaSO4, commonly called dead-burnt plaster. This material does not rehydrate and set properly, so option A explains the loss of the desired product.
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.
