Concentrated sulfuric acid (H2SO4) is used to dehydrate sugar in this classic (and dangerous) demonstration.
The sucrose (C12H22O11) is dehydrated to carbon and water. The water produced
by the sugar hydrates the sulfuric acid. The formation of strong hydrogen bonds between the acid and the water
makes the process strongly exothermic- enough heat is released to vaporize the hydrated sulfuric acid. The vapor
expands in pockets within the dehydrating sugar, making a porous black "tower" of carbon that rises out of the container.
Concentrated sulfuric acid
is extremely dangerous.
Choking sulfuric acid vapor will rise from the container. Do this demonstration in a fume hood.
The reaction takes a little while to get started, so don't be tempted to
dump more acid on the sugar if nothing seems to be happening. If you have a hood, use it.
For the procedure, refer to Bassam Shakhashiri's Chemical Demonstrations: A Handbook for Teachers of Chemistry,
Volume 1, pp 77-78 (1983).
Author: Fred Senese senese@antoine.frostburg.edu