Question

The difference of molecules of water in gypsum and plaster of paris is:
(correct answer +1, wrong answer -0.25)

• A. $\frac{5}{2}$
• B. $2$
• C. $\frac{3}{2}$
• D. $\frac{1}{2}$

Answer 1

The correct option is C $\frac{3}{2}$

Formula of plaster of paris = $CaS{O}_4.\frac{1}{2}{H}_{2}O$
Formula of gypsum= $CaS{O}_4.2H_{2}O$
Difference of water molecules in gypsum and plaster of paris is $CaS{O}_4.2H_{2}O-CaS{O}_4.\frac{1}{2}{H}_{2}O=2-\frac{1}{2}=\frac{3}{2}$