Water of crystallization

This is water found combined with a crystal in a fixed proportion. It is indicated in the formula name at the end following a dot. Crystals with water of crystallization are said to be hydrated, and those with no water of crystallization are said to be anhydrous. Hydrated copper(II) sulfate, CuSO₄.5H₂O, is blue, whereas the anhydrous salt, CuSO₄, is white. Hydrated salts are named so that the number of water molecules attached are made clear. In the example of CuSO₄.5H₂O the name is copper(II) sulfate-5-water.