Hydrates, Water in Crystals

In chemistry the term hydrates denote substances that contain water. The water molecules are either bound to a metal center or crystallized with the metal complex. 

Water of crystallization is water that occurs in crystals but is not covalently bonded to a host molecule or ion. An example of such a structure is NiCl2(H20)6. Thus 1/3 of the water molecules in the crystal are not directly bonded. Proteins crystallize with unusual large amounts of water (more than 50%) in the crystal lattice. 

Salts are compounds composed of a metal ion plus a non metal (or polyatomic) ion, e.g., sodium chloride (NaCl), and sodium phosphate (Na3P04). 

Hydrated salts (or Hydrates) are salts which have a definite amount of water chemically combined. Some common hydrates are  

This is called a copper (11) sulphate pentahydrate. The dot indicates an attractive force between the polar water molecules and the positively charged metal ion. On heating, the attractive forces are overcome and the water molecules are released 

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Karl Fischer titrations are frequently used for the analysis of water content in such samples as food materials, pharmaceuticals, and solvents used in industrial applications, or for the determination of hydration water in crystals. Dedicated units are commercially available and many automatic titra-tors or pH meters feature a connector for current biased voltage measurements labeled Karl-Fischer or simply KF . 

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