What is the chemical combination formula of Plaster of Paris? | General Science MCQ | Examoogle

Back to Practice Questions

General ScienceChemistry

Prev Next

What is the chemical combination formula of Plaster of Paris?

Option 1

Option 2

Option 3

Option 4

Correct Answer

🔬 SC • Science Concept & PrincipleGeneral ScienceChemistry

Option A

Option 1

Quick Summary:

Plaster of Paris, chemically known as calcium sulfate hemihydrate, is produced by the controlled heating of gypsum. Its chemical formula is $CaSO_4 \cdot \frac{1}{2}H_2O$ .

🔬SCScience SolutionConcept & Principle

💡 Explanation

Plaster of Paris, chemically known as calcium sulfate hemihydrate, is produced by the controlled heating of gypsum. Its chemical formula is $CaSO_4 \cdot \frac{1}{2}H_2O$ .

💡 Everyday Analogy (Real-World Intuition)

Think of it like a 'reset' button: you take a solid crystal, remove most of the water to create a fine powder (plaster), and when you add water later, it 'remembers' its original form and hardens back into a solid shape.

🧠 Memory Mnemonic / Shortcut Aid

Remember 'POP' for Plaster of Paris: 'Half a water, hard in a snap'.

🔢 Key Formulas

$CaSO_4 \cdot 2H_2O$ — Gypsum (Chemical raw material)

$CaSO_4 \cdot \frac{1}{2}H_2O$ — Plaster of Paris (Hemihydrate)

⚙️ Working Principle

When gypsum ( $CaSO_4 \cdot 2H_2O$ ) is heated at a temperature of approximately $373\text{ K}$ ( $100°\text{C}$ ), it loses three-fourths of its water of crystallization to form plaster of Paris. If heated above $373\text{ K}$ , it loses all its water to become 'dead burnt plaster' (anhydrous calcium sulfate). When mixed back with water, it rehydrates to form hard gypsum again, which is why it is used for casting and molding.

📌 Key Points

▸
Plaster of Paris is calcium sulfate hemihydrate.
▸
It is prepared by heating gypsum at $373\text{ K}$ .
▸
It has a rapid setting time when mixed with water.
▸
The reaction is $CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$ (setting process).

✅ Advantages

▸
Sets quickly into a hard mass.
▸
Excellent for casting intricate details.
▸
Fire-resistant properties.

❌ Disadvantages / Limitations

▸
Once hardened, it cannot be turned back into a moldable paste easily.
▸
Must be stored in moisture-proof containers to prevent premature setting.

🛠️ Applications / Uses

▸
Fixing fractured bones in orthopedic casts.
▸
Making decorative statues, toys, and architectural moldings.

📄 Additional Information

▸
Option A ( $CaSO_4 \cdot 2H_2O$ ) is Gypsum.
▸
Option C ( $CaSO_3 \cdot 2H_2O$ ) is Calcium Sulfite Dihydrate.
▸
Option D ( $CaCO_3 \cdot 2H_2O$ ) is not a standard stable compound.
▸
The hemihydrate notation can also be written as $(CaSO_4)_2 \cdot H_2O$ .

📊 Diagram / Illustration

✅

B is correct — Plaster of Paris is calcium sulfate hemihydrate represented by $CaSO_4 \cdot \frac{1}{2}H_2O$ .

Core Concepts Used

Click any tag to open in AI Tutor

Hydration Water of Crystallization Thermal Decomposition

💡 EXAM TIP

Always distinguish between Gypsum (dihydrate) and Plaster of Paris (hemihydrate); exams often swap the water stoichiometry to test your precision.

Was this solution helpful?

⚡ Practice on Android App · 4.8 ★

Solve 10,000+ More Questions with AI Tutor

Get instant step-by-step AI explanations, full shift Previous Year Papers (SSC GD, RRB, SSC JE), and regional rank analysis on the official Examoogle App.

Free Download • 100K+ Aspirants

Discussion (0)

Loading discussion...

Prev Next

Correct Answer

Solve 10,000+ More Questions with AI Tutor

Related Questions

Discussion (0)