Question

what is meany by "Water of crystallization"?​

Answer 1

chemistry, water of crystallization or water of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions.[1] In some contexts, water of crystallization is the total mass of water in a substance at a given temperature and is mostly present in a definite (stoichiometric) ratio. Classically, "water of crystallization" refers to water that is found in the crystalline framework of a metal complex or a salt, which is not directly bonded to the metal cation.

Upon crystallization from water or moist solvents, many compounds incorporate water molecules in their crystalline frameworks. Water of crystallization can generally be removed by heating a sample but the crystalline properties are often lost. For example, in the case of sodium chloride, the dihydrate is unstable at room temperature.

Coordination sphere of Na+ in the metastable dihydrate of sodium chloride (red = oxygen, violet = Na+, green = Cl−, H atoms omitted).[2]

Compared to inorganic salts, proteins crystallize with large amounts of water in the crystal lattice. A water content of 50% is not uncommon for proteins.

Answer 2

Water of crystallisation

$\to$Crystals of some compounds seem to be dry but actually contain some water molecules attached to them . this water is called water of crystallisation

or

$\to$Water of crystallisation is the fixed number of water molecules present in one Formula unit of a salt

Example :

# Gypsum (CaSO4)

# Blue vitriol (CuSO4)

Note :

$\to$Common salt (NaCl) , Sugar (C12H12O11) are do not contain water of crystallisation