Water of Crystallisation
Water molecules chemically bound within the crystal lattice of a hydrated salt in a fixed stoichiometric ratio.
Unit
mol per mol
In depth
These molecules occupy defined lattice positions and are responsible for the shape, colour and stability of many crystals. Removing them collapses the lattice, usually producing a powder of different colour. The energy required to expel them is far smaller than a covalent bond but far larger than simple surface wetting.
Examples in the real world
The five water molecules in CuSO₄·5H₂O; heating the blue crystals to 250 °C leaves a white anhydrous powder.