[2][3] A colorful example is cobalt(II) chloride, which turns from blue to red upon hydration, and can therefore be used as a water indicator.
Some anhydrous compounds are hydrated so easily that they are said to be hygroscopic and are used as drying agents or desiccants.
The state of hydration of an active pharmaceutical ingredient can significantly affect the solubility and dissolution rate and therefore its bioavailability.
Nonpolar molecules such as methane can form clathrate hydrates with water, especially under high pressure.
In such cases the guest–host hydrogen bonds result in the formation of L-type Bjerrum defects in the clathrate lattice.
[7][8] The stability of hydrates is generally determined by the nature of the compounds, their temperature, and the relative humidity (if they are exposed to air).