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Video Example : Water of crystallization

Water of crystallization

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Definition of Water of crystallization

In crystallography, water of crystallization or water of hydration or crystallization water is water that occurs inside crystals. OR Water of crystallization is water that is stoichiometrically bound into a crystal.

More About Water of crystallization

  • Water of crystallization is the number of water molecules, chemically combined in a definite molecular proportion, with the salt in its crystalline state
  • Water is often necessary for the formation of crystals
  • In some contexts, water of crystallization is the total weight of water in a substance at a given temperature and is mostly present in a definite ratio
  • "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
  • Water of crystallization can generally be removed by heating a sample but the crystalline properties are often los
  • Crystal salts containing water of crystallization are called hydrates
  • Heat a few crystals of copper sulphate in a dry boiling tube
  • Copper sulphate crystals become colourless and water droplets are observed in the boiling tube
  • Copper sulphate crystals which seem to be dry contain water of crystallization
  • When we heat the crystals, this water is removed and the crystals turn white in color
  • When we add water, the color is restored
  • 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. Chemical formula for hydrated copper sulphate is
  • One other salt, which possesses water of crystallization, is gypsum
  • It has two water molecules as water of crystallization
  • Gypsum has the formula CaSO4 2H2O
  • On heating, gypsum loses water molecules and forms calcium sulphate hemihydrate, that is, Plaster of Paris which is used for plastering fractured bones and for making toys
  • Plaster of Paris has half water molecule associated with one molecule of the salt CaSO4 ½ HO
  • CaSO4 ½ H2O