Why does plaster of Paris become hard when water is added?
Answer and explanation
Correct answer: It changes into gypsum
Plaster of Paris is calcium sulphate hemihydrate, CaSO₄·½H₂O. When water is added, it rehydrates and changes back into gypsum, calcium sulphate dihydrate, CaSO₄·2H₂O. The re-formed crystals interlock and make the material set into a hard mass, so option A is correct. It does not form sodium chloride, turn into a gas, or produce sugar.
Frequently asked questions
What is the correct answer to this question?
It changes into gypsum
Why is this the correct answer?
Plaster of Paris is calcium sulphate hemihydrate, CaSO₄·½H₂O. When water is added, it rehydrates and changes back into gypsum, calcium sulphate dihydrate, CaSO₄·2H₂O. The re-formed crystals interlock and make the material set into a hard mass, so option A is correct. It does not form sodium chloride, turn into a gas, or produce sugar.
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.
