Setting of plaster of paris is

Options

A. Dehydration
B. Oxidation with atmospheric `CO_(2)`
C. Combination with atmospheric `CO_(2)`
D. Hydration to yield another hydrate

Answer

**Step-by-Step Solution:**

1. **Understanding Plaster of Paris**: Plaster of Paris is chemically represented as \( \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} \). It is a white powder that hardens when mixed with water.

2. **Hydration Process**: The setting of plaster of Paris involves a chemical reaction known as hydration. In this process, plaster of Paris reacts with water.

3. **Chemical Reaction**: The reaction can be represented as:
\[ \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} + \frac{3}{2} \text{H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \]
Here, plaster of Paris reacts with water to form gypsum, which is represented as \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \).

4. **Formation of Gypsum**: The product of this reaction is gypsum, which is another hydrate. Gypsum contains more water in its structure compared to plaster of Paris.

5. **Exothermic Nature**: The setting of plaster of Paris is an exothermic process, meaning it releases heat during the reaction.

6. **Conclusion**: Therefore, the setting of plaster of Paris involves hydration to yield another hydrate (gypsum), and this process is exothermic.

**Final Answer**: The setting of plaster of Paris is hydration to yield another hydrate (gypsum), and it is an exothermic process.

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