Question

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

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

Answer 1

The correct option is B

Baking soda

Explanation for the correct options:

(B) Baking soda

• Baking soda is sodium bicarbonate$\left({\mathrm{NaHCO}}_3\right)$.
• It is present in an anhydrous form without any water for crystallization.
• It is used as a dry fire extinguisher because of its alkali nature.
• When sodium bicarbonate is heated by the fire it becomes sodium carbonate.

Explanation for the incorrect options:

(A) Blue vitriol

• Blue vitriol is copper sulfate pentahydrate $\left({\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}\right)$ and it has 5 molecules of water.

(C) Washing soda

• Washing soda is a sodium carbonate monohydrate $\left({\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}\right)$ and it also 10 molecules of contains water.

(D) Gypsum

• Gypsum is calcium sulfate dihydrate $\left({\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\right)$ and it can be used as fertilizer.

Hence, option (B) is correct, baking soda does not contain water for crystallization.