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 combines with the powder and re-forms gypsum, CaSO₄·2H₂O. The new gypsum crystals interlock and produce a hard solid, which is why plaster is used for casts and moulds. No sodium chloride, gas, or sugar is formed. Option A is correct.
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 combines with the powder and re-forms gypsum, CaSO₄·2H₂O. The new gypsum crystals interlock and produce a hard solid, which is why plaster is used for casts and moulds. No sodium chloride, gas, or sugar is formed. 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.
