Concentrated sulfuric acid has a powerful dehydrating property, removing water () from other chemical compounds such as table sugar (sucrose) and other carbohydrates, to produce carbon, steam, and heat. Dehydration of table sugar (sucrose) is a common laboratory demonstration. The sugar darkens as carbon is formed, and a rigid column of black, porous carbon called a carbon snake may emerge as shown in the figure.
Similarly, mixing starch into concentrated sulfuric acid gives elemental carbon and water. The effect of this can be seen when concentrated sulfuric acid is spilled on paper, which is composed of cellulose; the cellulose reacts to give a burnt appearance in which the carbon appears much like soot that results from fire.
Although less dramatic, the action of the acid on cotton, even in diluted form, destroys the fabric.
The reaction with copper(II) sulfate can also demonstrate the dehydration property of sulfuric acid. The blue crystals change into white powder as water is removed: