Why can the quality of plaster of Paris be spoiled by overheating gypsum?
Answer and explanation
Correct answer: More water than needed for hemihydrate can be removed
The governing concept is controlled dehydration of gypsum. Gypsum is calcium sulfate dihydrate, CaSO4·2H2O. On moderate heating it loses part of its water and forms plaster of Paris, calcium sulfate hemihydrate, CaSO4·½H2O. Excessive heating can remove still more water and produce an unsuitable anhydrous form, so the material may not set properly. Therefore option A is correct; gypsum does not become sodium chloride, calcium does not escape as a gas, and chlorine is not added.
Frequently asked questions
What is the correct answer to this question?
More water than needed for hemihydrate can be removed
Why is this the correct answer?
The governing concept is controlled dehydration of gypsum. Gypsum is calcium sulfate dihydrate, CaSO4·2H2O. On moderate heating it loses part of its water and forms plaster of Paris, calcium sulfate hemihydrate, CaSO4·½H2O. Excessive heating can remove still more water and produce an unsuitable anhydrous form, so the material may not set properly. Therefore option A is correct; gypsum does not become sodium chloride, calcium does not escape as a gas, and chlorine is not added.
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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
