Question

The chemical formula of Plaster of Paris is:

• A. \( \text{CaSO}_4 \cdot 3\text{H}_2\text{O} \)
• B. \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \)
• C. \( \text{CaSO}_4 \cdot \text{H}_2\text{O} \)
• D. \( \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} \)

Hint:

Plaster of Paris is made by heating gypsum (\( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \)) to remove part of the water content, resulting in \( \text{CaSO}_4 \cdot \text{H}_2\text{O} \).

Answer 1

The Correct Option is C

Plaster of Paris is chemically known as calcium sulfate hemihydrate. Its formula is: \[ \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} \]
This means that for every molecule of calcium sulfate, half a molecule of water is attached. When Plaster of Paris is mixed with water, it forms a hard solid, making it useful for making casts and molds.
Thus, the correct formula for Plaster of Paris is \( \text{CaSO}_4 \cdot \text{H}_2\text{O} \), which is option (C).