hydraat

Hydraat (hydrate) is a chemical compound that includes water molecules within its solid structure or in association with the compound through hydrogen bonding. Most hydrates are described by a formula of the form A · xH2O, where x denotes the number of water molecules per formula unit. The water is known as water of crystallization or hydration; in many cases it is an integral part of the crystal lattice.

Hydrates can be classified as stoichiometric, with a fixed water content, or nonstoichiometric, where the degree of hydration can vary with temperature, humidity, or chemical environment. Upon heating, hydrates typically lose their water in a dehydration process, often yielding anhydrous salts or other anhydrous products. The appearance and properties of the substance can change during dehydration; for example, copper(II) sulfate pentahydrate CuSO4 · 5H2O is blue, while the anhydrous CuSO4 is white.

Common examples include copper(II) sulfate pentahydrate (CuSO4 · 5H2O), magnesium sulfate heptahydrate (MgSO4 · 7H2O, Epsom salt), and calcium sulfate dihydrate (CaSO4 · 2H2O, gypsum). Some hydrates are used industrially as drying agents or in cement chemistry, while hydrated salts can serve as reliable sources of water in storage or as reactants in synthesis. In nature, water of crystallization is found in minerals, and a related class, clathrate hydrates, traps gas molecules within a water lattice under high pressure, with significance for natural gas deposits and potential energy resources.