Hydrate
A crystalline compound in which a definite number of water molecules is incorporated into the lattice.
Formula / equation
MX·nH₂O
Unit
Dimensionless
In depth
The water is held at specific lattice sites, often coordinated to a metal cation, and its amount is fixed by stoichiometry rather than by ambient humidity. Gentle heating drives it off stepwise, and the resulting mass loss is a standard gravimetric way to determine n.
Examples in the real world
CuSO₄·5H₂O (blue vitriol), Na₂CO₃·10H₂O (washing soda) and CaSO₄·2H₂O (gypsum).