hydrates

Hydrates
A //hydrate// is an ionic compound that contains water molecules as part of their crystal lattice.

The water molecules are usually present in whole-number ratios compared to the salt compound. A prefix (like di-, tri-, etc.) will be used in the formula's name to indicate the number of waters.

A hydrate's chemical formula uses a little dot, "**·**" to separate the salt formula from its waters.

For example, the mineral hydrohalite is sodium chloride dihydrate, which has a chemical formula of NaCl**·**2 H 2 O.

Here is a model of the crystal structure of hydrohalite:



Some other examples of hydrates include:
 * calcium chloride dihydrate, CaCl 2 **·**2 H 2 O
 * sodium acetate trihydrate, NaC 2 H 3 O 2 **·**3 H 2 O
 * magnesium sulfate heptahydrate, MgSO 4 **·**7 H 2 O
 * sodium phosphate dodecahydrate, Na 3 PO 4 **·**12 H 2 O