Why does plaster of Paris harden 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 re-forms gypsum, calcium sulphate dihydrate, CaSO₄·2H₂O. The newly formed interlocking gypsum crystals set into a hard mass, which is why the material is useful for casts and moulds. Thus option A is correct; no sodium chloride, carbon dioxide, or sugar is formed in this setting reaction.
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 re-forms gypsum, calcium sulphate dihydrate, CaSO₄·2H₂O. The newly formed interlocking gypsum crystals set into a hard mass, which is why the material is useful for casts and moulds. Thus option A is correct; no sodium chloride, carbon dioxide, or sugar is formed in this setting reaction.
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.
