CBSE Class 10 Science 2021 Term 1 Solved Paper

Question : 30

Total: 60

Which of the following salts do not have the water of crystalisation?
(i) Bleaching Powder
(ii) Plaster or Paris
(iii) Washing soda
(iv) Baking soda

(ii) and (iv)
(i) and (iii)
(ii) and (iii)
(i) and (iv)

Solution:

The water of crystallisation means having a fixed number of molecules present in one formula of a unit of salt.
(i) Bleaching powder has the chemical formula CaOCl2. Its formula does not show any association with water molecules.
(ii) Plaster of Paris has the chemical formula CaSO4⋅1∕2H2O. In its formula, 1∕2H2O represents water of crystallization.
(iii) Washing soda is sodium carbonate decahydrate Na2CO3⋅10H2O which means it contains 10 water of crystallisation.
(iv) Baking soda is sodium bicarbonate (NaHCO3) in anhydrous form without any water of crystallisation.
Thus, bleaching powder and baking soda do not have any water of crystallisation.

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