Why does plaster of Paris harden when water is added?
Answer and explanation
Correct answer: It changes into gypsum
The governing concept is rehydration and setting of plaster of Paris. Plaster of Paris is calcium sulphate hemihydrate, CaSO4·1/2H2O. When water is added, it combines with the material and converts it back into gypsum, CaSO4·2H2O. The newly formed crystalline gypsum interlocks and makes the mixture hard. Therefore option A is correct; no sodium chloride, gas, or sugar is produced 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?
The governing concept is rehydration and setting of plaster of Paris. Plaster of Paris is calcium sulphate hemihydrate, CaSO4·1/2H2O. When water is added, it combines with the material and converts it back into gypsum, CaSO4·2H2O. The newly formed crystalline gypsum interlocks and makes the mixture hard. Therefore option A is correct; no sodium chloride, gas, or sugar is produced 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.
