Why does plaster of Paris become hard when water is added?
Answer and explanation
Correct answer: It changes into gypsum
The governing concept is rehydration followed by setting. Plaster of Paris is calcium sulphate hemihydrate, CaSO4·½H2O. When water is added, it combines with the compound and reforms gypsum, CaSO4·2H2O. This hydration reaction produces a hard solid mass. It does not form sodium chloride, gas or sugar, so A is the only suitable answer.
Frequently asked questions
What is the correct answer to this question?
It changes into gypsum
Why is this the correct answer?
The governing concept is rehydration followed by setting. Plaster of Paris is calcium sulphate hemihydrate, CaSO4·½H2O. When water is added, it combines with the compound and reforms gypsum, CaSO4·2H2O. This hydration reaction produces a hard solid mass. It does not form sodium chloride, gas or sugar, so A is the only suitable answer.
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.
