How to Make "Black Snakes" Through a Sulfuric Acid and Sugar Reaction

Dehydration of Sugar Is More Exciting Than It Sounds

A flask of sulfuric acid with glassware containing carbon, a result of adding the acid to sugar
When you react sugar and sulfuric acid you get carbon as a product.

Andy Crawford,Tim Ridley/Getty Images

Want to amaze your friends with your scientific wizardry? One of the most spectacular chemistry demonstrations is also one of the simplest. It's the dehydration of sugar (sucrose) with sulfuric acid. When you do this you, you create a bizarre and impressive "black snake" that emerges from your beaker!

How to Create "Black Snakes"

Basically, all you do is put ordinary table sugar in a glass beaker and stir in some concentrated sulfuric acid (you can dampen the sugar with a small volume of water before adding the sulfuric acid).

The sulfuric acid removes water from the sugar in a highly exothermic reaction, releasing heat, steam, and sulfur oxide fumes. Aside from the sulfurous odor, the reaction smells a lot like caramel. The white sugar turns into a black carbonized tube that pushes itself out of the beaker.

The Chemistry of How They're Formed

Sugar is a carbohydrate, so when you remove the water from the molecule, you're basically left with elemental carbon. Carbon, of course, is black. The dehydration reaction is a type of elimination reaction.
C12H22O11 (sugar) + H2SO4 (sulfuric acid) → 12 C (carbon) + 11 H2O (water) + mixture water and acid
Although the sugar is dehydrated, the water isn't 'lost' in the reaction. Some of it remains as a liquid in the acid. Since the reaction is exothermic (heat-generating), much of the water is boiled off as steam.

Safety Precautions

If you do this demonstration, use proper safety precautions. Whenever you deal with concentrated sulfuric acid, you should wear gloves, eye protection, and a lab coat. Avoid standing over the beaker during the experiment or inhaling the steam generated. After the beaker has cooled, you can pull out the carbon and remove the residue from the glassware with acetone. It's preferable to perform the demonstration inside of a fume hood.