Illustrated Glossary of Organic Chemistry

Hydration: A process which adds water. A substance which absorbs water spontaneously from its surroundings is hygroscopic. A hygroscopic substance which absorbs so much water that it becomes an aqueous solution of the substance is deliquescent.

In this hydration reaction, 1-methylcyclohexene (an alkene) is reacted with aqueous H3O+ (formed from water and a strong acid such as H2SO4), resulting in Markovnikov addition of water across the pi bond. The product is an alcohol.

Syn, anti-Markovnikov addition of water to an alkene can be achieved via a hydroboration-oxidation reaction.

CoCl2 anhydrous
Addition of water to anhydrous CoCl2 (blue) forms the hexahydrate (red). Click to watch a CoCl2 dehydration/hydration video.