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 water and changes into gypsum, CaSO₄·2H₂O. This hydration reaction produces a solid mass, so the material sets and becomes hard. Sodium chloride, gas, and sugar are not products of this setting reaction; therefore, 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 water and changes into gypsum, CaSO₄·2H₂O. This hydration reaction produces a solid mass, so the material sets and becomes hard. Sodium chloride, gas, and sugar are not products of this setting reaction; therefore, 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.
