Hydrate
Definition and meaning of Hydrate in chemistry.
Hydrate is a compound that incorporates a fixed, stoichiometric number of water molecules into its crystal structure. This water, called water of hydration (or water of crystallization), is held within the solid lattice rather than simply mixed in.
In more detail
Hydrates typically form when an ionic salt crystallizes from aqueous solution, trapping water molecules at specific lattice sites. The water may coordinate directly to a metal cation, as in many transition metal salts, or be held in place by hydrogen bonds to the anion. Because the ratio is fixed, hydrates are written with a centered dot in their formula, distinguishing them from an arbitrary wet mixture. Heating a hydrate drives off this water (dehydration), often producing a striking color change and leaving the anhydrous salt behind.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Example formula | CuSO4·5H2O |
| Also called | Water of crystallization / water of hydration |
| Related processes | Dehydration (loses water); deliquescence (gains water) |
Copper(II) sulfate pentahydrate, CuSO4·5H2O, is a blue crystalline solid; heating it drives off the water, leaving white anhydrous copper(II) sulfate, CuSO4.
Frequently asked questions
What happens when a hydrate is heated?
Heat breaks the bonds holding water in the crystal lattice, releasing it as vapor and leaving the anhydrous compound behind, often with a visible color or texture change.
Is a hydrate the same as a wet compound?
No. A hydrate has a fixed, definite ratio of water molecules per formula unit, unlike a wet solid, which can hold an arbitrary, variable amount of surface moisture.