Question

Copper sulphate crystals which seem to be dry contain water of crystallization. When we heat the crystals, this water is removed and the salt turns white. If you moisten the crystals again with water, you will find that blue colour of the crystals reappears.

The water of crystallization is the fixed number of water molecules present in one formula unit of a salt. Five water molecules are present in one formula unit of copper sulphate. The chemical formula for hydrated copper sulphate is $Cu{SO}_4$. $5H_{2}O$. Now you would be able to answer the question whether the molecule of ${Na}_2{CO}_3$. $10H_{2}O$ is wet. One other salt, which possesses water of crystallization is gypsum. It has two water molecules as a water of crystallization. It has the formula $Ca{SO}_4$. $2H_{2}O$.

What are the uses of this salt?

Answer 1

$N{a}_{2}C{O}_3.10H_{2}O$ is dry. The $10H_{2}O$ represents the water of crystallization.

Gypsum with formula $CaS{O}_4.2H_{2}O$ is used for many purposes:

$⟶$ Used as a soil additive (sometimes called Land Plaster) to improve soils' workability and receptivity to moisture.

$⟶$ Used as an additive in turbid water, particularly ponds, to settle dirt and clay particles without injuring aquatic life.

$⟶$ As a food additive as a dietary source of $Ca$.

$⟶$ As a color additive for drugs and cosmetics.

$⟶$ As a primary ingredient in toothpaste.