monohydrate

A monohydrate is a chemical compound that includes exactly one molecule of water per formula unit in its crystalline structure. Water that is integrated into the structure as crystals is referred to as water of hydration or crystallization. In chemical notation, a monohydrate is written with a dot followed by H2O, for example copper(II) sulfate monohydrate, CuSO4·H2O.

Monohydrates are part of the broader class of hydrates, which vary in the number of water molecules associated with each formula unit. They form by crystallization from aqueous solutions or by drying and rehydrating solid hydrates under controlled humidity. The water molecules in a monohydrate are typically bound within the crystal lattice and can influence properties such as solubility, stability, and color. Removal of the water—dehydration—yields the anhydrous form; in many cases dehydration is reversible if humidity is restored.

Nomenclature and relationships: The term monohydrate indicates one water molecule per formula unit. Depending on the compound, dehydration may lead directly to the anhydrous material or to another hydrate form. Some hydrates can transition between different hydration states under different conditions of temperature and humidity.

Examples and applications: Copper(II) sulfate monohydrate is among the best-known monohydrates and is widely used in teaching laboratories and as a reagent. Hydrates, including monohydrates, are important in crystallography, pharmaceuticals, and chemical manufacturing because hydration state can affect solubility, melting point, and stability.