What is the amount of water per unit of calcium sulphate in plaster of Paris?
Answer and explanation
Correct answer: Half water molecule
The governing concept is the distinction between hydrates and hemihydrates. Plaster of Paris is calcium sulphate hemihydrate, represented as CaSO₄·½H₂O. Thus, one formula unit of calcium sulphate is associated with half a water molecule on average. Option A is correct. Gypsum contains two water molecules per calcium sulphate unit, while the other choices describe different or incorrect hydration states.
Frequently asked questions
What is the correct answer to this question?
Half water molecule
Why is this the correct answer?
The governing concept is the distinction between hydrates and hemihydrates. Plaster of Paris is calcium sulphate hemihydrate, represented as CaSO₄·½H₂O. Thus, one formula unit of calcium sulphate is associated with half a water molecule on average. Option A is correct. Gypsum contains two water molecules per calcium sulphate unit, while the other choices describe different or incorrect hydration states.
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.
