Ionic compounds that can trap water in their crystalline structure are called hydrates. A term is added following the formula or name of the compound to indicate that it is trapping water, and to show the ratio of trapped water molecules to the ions in the compound.
Add “•n H2O” after a formula, where “n” is a whole number giving the number of water molecules per unit of the compound: CuSO4•5 H2O.
Add “___hydrate” after a name using a prefix to indicate the ratio of water molecules per unit compound: copper(II) sulfate pentahydrate.
