Question

The formula of plaster of Paris is —

• A. CaSO4·\(\frac{1}{2}\)H2O
• B. CaSO4·2H2O
• C. CaSO4·H2O
• D. CaSO4·5H2O

Hint:

POP is formed by partial dehydration of gypsum. When mixed with water, it reforms gypsum, which hardens quickly.

Answer 1

The Correct Option is A

Step 1: Recall the composition of plaster of Paris.
Plaster of Paris (POP) is a white powder obtained by heating gypsum at 373 K. Gypsum has the formula CaSO4·2H2O. On heating, it loses 1.5 molecules of water and forms POP.
Step 2: Chemical reaction.
\[ \text{CaSO}_4·2\text{H}_2\text{O} \xrightarrow{heat} \text{CaSO}_4·\frac{1}{2}\text{H}_2\text{O} + \frac{3}{2}\text{H}_2\text{O} \] Step 3: Conclusion.
Hence, the chemical formula of plaster of Paris is \(\text{CaSO}_4·\frac{1}{2}\text{H}_2\text{O}\).