Plaster of Paris (Preparation) MCQs Quiz | Class 10
This quiz covers Class X Science (Code 086), Unit I: Chemical Substances – Nature and Behaviour, specifically focusing on the preparation of Plaster of Paris from gypsum and the heating process involved. Complete the 10 questions below to test your understanding, view your score, and download the solution PDF for revision.
Overview of Plaster of Paris (PoP)
Plaster of Paris is chemically known as Calcium Sulphate Hemihydrate. Its chemical formula is CaSO4.1/2H2O. It is prepared by heating Gypsum (CaSO4.2H2O) at a controlled temperature of 373 K (100 degrees Celsius). The substance gets its name because it was historically manufactured from abundant gypsum deposits near Paris.
Preparation Method
The preparation involves a thermal decomposition reaction where gypsum loses water molecules partially.
Reaction:
CaSO4.2H2O (Gypsum) -> CaSO4.1/2H2O (Plaster of Paris) + 1.5 H2O
During this process, it is crucial to maintain the temperature at exactly 373 K. At this temperature, gypsum loses three-fourths of its water of crystallization to form Plaster of Paris.
Critical Temperature Control
If the temperature rises above 373 K during heating, all water of crystallization is lost. The resulting product is anhydrous calcium sulphate (CaSO4), also known as Dead Burnt Plaster. Dead burnt plaster does not have the setting property when mixed with water, making it useless for the typical applications of PoP.
Key Properties and Storage
- White Powder: PoP is a fine white powder.
- Setting Property: When mixed with water, it rehydrates to form hard solid gypsum within half an hour, releasing heat (exothermic process).
- Storage: Since it absorbs moisture from the air to form hard gypsum, it must always be stored in moisture-proof containers.
Quick Revision Table
| Compound | Chemical Name | Formula |
|---|---|---|
| Gypsum | Calcium Sulphate Dihydrate | CaSO4.2H2O |
| Plaster of Paris | Calcium Sulphate Hemihydrate | CaSO4.1/2H2O |
| Dead Burnt Plaster | Anhydrous Calcium Sulphate | CaSO4 |
Extra Practice Questions
- 1. Why is the formula of Plaster of Paris written with half a water molecule? (Ans: Two formula units of CaSO4 share one molecule of water).
- 2. Write the chemical equation for the setting of Plaster of Paris.
- 3. What happens if gypsum is heated to 400 K?
- 4. Name the raw material used for making chalks and casts.
- 5. Why is Plaster of Paris used for supporting fractured bones?
Content created and reviewed by the CBSE Quiz Editorial Team based on the latest NCERT textbooks and CBSE syllabus. Our goal is to help students practice concepts clearly, confidently, and exam-ready through well-structured MCQs and revision content.