Example Group (EN): Dehydration of sucrose


#1

Dehydration of sucrose is a simple, yet impressive experiment where sugar (sucrose) “turns” into “pure” carbon. The only additional component needed is concentrated sulfuric acid (we will explain later why dilute sulfuric acid will not work).

In the picture below you can see what the “created” carbon looks like:

Picture by Prof. Blume; http://www.chemieunterricht.de

  1. A beaker is filled with sucrose, which consists of three elements: carbon,hydrogen and oxygen. Looking at sucrose’s chemical formula (C12 H22O11) we see that 11 molecules of water have exactly the same amount of hydrogen and oxygen atoms.
    Sucrose.wal (20.9 KB)

  2. Concentrated sulfuric acid is added. In the following reactions sugar is dehydrated. One possible reaction happens between water and sulfuric acid yielding H3O+ ions. The second possibility is the formation of hydrates (H2SO4*n H2O). This also explains why only concentrated sulfuric acid will work, as dilute acid has already reacted with water).
    SulfuricAcid_Water.wal (13.1 KB)

  3. After these reactions “pure” carbon is left, which has expanded into a porous, black cylinder due to the exothermic reaction and the generation of steam and gas (this is why such an experiment should only be performed in a fume cupboard). Porous carbon like this has a great surface area and can e.g. be used as activated carbon.
    Carbon.wal (25.7 KB)