Question

What is the chemical formula of the Plaster of Paris?

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

Hint:

Plaster of Paris is formed by heating gypsum (CaSO\(_4\) \(\cdot\) 2H\(_2\)O) and removing part of its water content, which results in the formula CaSO\(_4\) \(\cdot\) \(\frac{1}{2}\)H\(_2\)O.

Answer 1

The Correct Option is C

Step 1: Understanding Plaster of Paris.
Plaster of Paris is a fine, white powder obtained by heating gypsum (CaSO\(_4\) \(\cdot\) 2H\(_2\)O). When mixed with water, it hardens and is widely used in construction and molding. Its chemical formula is CaSO\(_4\) \(\cdot\) \(\frac{1}{2}\)H\(_2\)O.
Step 2: Analysis of options.
- (1) CaSO\(_4\): Incorrect, this represents the basic form of calcium sulfate, not the hydrated form of Plaster of Paris.
- (2) CaSO\(_4\) \(\cdot\) 2H\(_2\)O: Incorrect, this is the formula of gypsum, not Plaster of Paris.
- (3) CaSO\(_4\) \(\cdot\) \(\frac{1}{2}\)H\(_2\)O: Correct, this is the formula of Plaster of Paris.
- (4) CaSO\(_4\) \(\cdot\) 2H\(_2\)O\(_2\): Incorrect, this is not the correct formula for Plaster of Paris.
Step 3: Conclusion.
Thus, the correct answer is (3) CaSO\(_4\) \(\cdot\) \(\frac{1}{2}\)H\(_2\)O.