Plaster of Paris loses its usefulness when kept open for a long time. What is the best reason?
Answer and explanation
Correct answer: It can absorb moisture and change into gypsum
Plaster of Paris is calcium sulfate hemihydrate, CaSO₄·½H₂O. It is intended to react with added water and set into gypsum, CaSO₄·2H₂O. If exposed to humid air before use, it can slowly absorb moisture and become gypsum prematurely. The partly hydrated material loses its ability to set properly when later mixed for application. Thus option C gives the correct reason; the other products are unrelated.
Frequently asked questions
What is the correct answer to this question?
It can absorb moisture and change into gypsum
Why is this the correct answer?
Plaster of Paris is calcium sulfate hemihydrate, CaSO₄·½H₂O. It is intended to react with added water and set into gypsum, CaSO₄·2H₂O. If exposed to humid air before use, it can slowly absorb moisture and become gypsum prematurely. The partly hydrated material loses its ability to set properly when later mixed for application. Thus option C gives the correct reason; the other products are unrelated.
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.
