Carbon Snake Demo (Sugar and Sulfuric Acid)


Carbon snake chemistry demo
The carbon snake is a chemistry demonstration in which sugar and sulfuric acid react to produce a column of black carbon. (Photo: Thee.p, Creative Commons)

The reaction between sugar and sulfuric acid is one of the simplest chemistry demonstrations and also one of the most spectacular. The chemical reaction causes the dehydration of sugar. This results in a growing, steaming black column of carbon that smells like a combination of caramel and rotten eggs. The demonstration is also called the dehydration of sugar or the carbon snake.

Materials

All you need is ordinary granulated sugar (sucrose) and concentrated sulfuric acid. The type of sugar isn’t critical. If all you have is powdered sugar or some sugar besides sucrose, use that. If you don’t have access to lab chemicals, hardware stores sometimes sell concentrated sulfuric acid as a drain cleaner. Check the label to make sure the key ingredient is sulfuric acid. The reaction is exothermic, producing enough heat that it may shatter the container. Choose glassware you’re willing to sacrifice.

  • Granulated sugar (sucrose)
  • Concentrated sulfuric acid (H2SO4)
  • Glass container

What to Do

The instructions couldn’t be easier!

  1. Fill your glass container with granulated sugar.
  2. Stir in concentrated sulfuric acid.
  3. Move away to enjoy the reaction once the black “snake” starts to grow.

The Science of Mixing Sugar and Sulfuric Acid

This is an example of a dehydration reaction. Basically, the acid removes water from the carbohydrate, which is sucrose.

C12H22O11 (sugar) + H2SO4 (sulfuric acid)  + 1/2 O2 (oxygen from the air) → 11 C (carbon) + CO2 + 12 H2O (water) + SO2

The reaction releases water, which dilutes the sulfuric acid, producing heat. Some of the water is converted to steam by heat. The black product of the reaction is carbon in the forms of graphite and amorphous carbon. The sugar yields the burned caramel odor, while sulfur dioxide contributes the stench of rotten eggs.

Safety

Sulfuric acid is a strong acid. Splashes can eat clothing, damage surfaces, and cause serious chemical burns. You should wear safety goggles, gloves, and protective clothing. Tie back long hair. Ideally, perform the sugar and sulfuric acid demonstration inside a fume hood. Otherwise, select a well-ventilated area, such as an outdoor space. Clean-up basically involves throwing away the glassware, since the burnt sugar isn’t easy to scrape off. Sprinkle baking soda (a weak base) over the demonstration and rinse it with water to neutralize any excess acid.

Chem Demos Like the Sugar and Sulfuric Acid Reaction

A more dramatic reaction results from mixing para-nitroaniline (p-nitroaniline) and sulfuric acid. To perform this demonstration, heat p-nitroaniline and sulfuric acid in a fume hood. The reaction doesn’t immediately occur, but when it does, a black column shoots from the glassware. Be careful, though. If there is too much sulfuric acid, the reaction can explode.

The carbon snake demo is often confused with the black snake demo. Black snakes are smaller columns of carbon produced by the reaction between sugar and baking soda. The reaction isn’t spontaneous. It requires a fuel and ignition source.

The elephant toothpaste and kid-friendly elephant toothpaste are two more exothermic reactions. These demonstrations produce columns of foam.

See the Dehydration of Sugar in Action

Here’s what to expect from this demonstration.

References

  • Roesky, Herbert W. (2007). “Experiment 6: Sugar coal by splitting off water from sugar with sulfuric acid”. Spectacular Chemical Experiments. Wiley. p. 17. ISBN 978-3-527-31865-0.
  • Shakhashiri, Bassam Z.; Shreiner, Rodney; Bell, Jerry A. (2011). “1.32 Dehydration of Sugar by Sulfuric Acid”. Chemical Demonstrations: A Handbook for Teachers of Chemistry Volume 1. University of Wisconsin press. pp. 77–78. ISBN 978-0-299-08890-3.

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