Illustrated Glossary of Organic Chemistry

Dehydration (desiccation): A process such as a chemical reaction that removes water.

Reaction of 1-methyl-1-cyclohexanol with aqueous sulfuric acid results in dehydration and formation of an alkene product. The atoms which constitute the molecule of water that is removed are shown in red. The reaction follows the E1 mechanism, as shown in this example.

CoCl26 H2O
Anhydrous CoCl2
Gently heating CoCl2 . 6 H2O (red) causes it to dehydrate. The product is anhydrous CoCl2 (blue). Watch a time lapse video.

Sucrose + H2SO4

Carbon + water vapor (steam)
The modern term 'carbohydrate' is a contraction of 'carbon hydrate'. Carbohydrates such as sucrose (C12H22O11) where once thought of as 'carbon hydrates', having one molecule of water bonded to each carbon atom,  giving a molecular formula approximating C12(H2O)12. While this is not an accurate structure for sucrose, its reaction with concentrated H2SO4 (a dehydrating agent) does produce carbon and water vapor (steam). Watch a video of this reaction.