Question

Which of the following salts does not contain water of crystallisation?

• A. Baking soda
• B. Blue vitriol
• C. Washing soda
• D. Gypsum

Answer 1

The correct option is B Blue vitriol

The water of crystallisation denotes the number of water molecules present in the crystal structure of salts.

The table given below is showing the chemical formula of the given chemical compounds.
$$\begin{array}{ccc}\text{Chemical compound}& \text{Formula}& \text{No. of water molecules}\\ \text{Baking soda}& {\text{NaHCO}}_3& \text{0}\\ \text{Blue vitriol}& {\text{CuSO}}_4.5{\text{H}}_2\text{O}& \text{5}\\ \text{Washing soda}& {\text{Na}}_2{\text{CO}}_3.10{\text{H}}_2\text{O}& \text{10}\\ \text{Gypsum}& {\text{CaSO}}_4.2{\text{H}}_2\text{O}& \text{2}\end{array}$$
So from the table, it is clear that only baking soda does not contain water of crystallisation.