Question

A paste of substance $A$ is used to decorate the ceiling of your home.

Write the reaction of substance A with $H_{2}O$.

Answer 1

$CaS{O}_4.\frac{1}{2}{H}_{2}O+\frac{3}{2}{H}_{2}O\to CaS{O}_4.2H_{2}O$

$CaS{O}_4.2H_{2}O\left(A\right)$ is known as gypsum which is used to decorate the ceiling of our homes.