Carbon snake

A column of porous graphite formed during the experiment.

Carbon snake is a demonstration of the dehydration reaction of sugar by concentrated sulfuric acid. With concentrated sulfuric acid, granulated table sugar (sucrose) performs degradation reaction which changes its form to black solid-liquid mixture.[1] Carbon snake experiment can sometimes be misrecognized as black snake, "sugar snake," or "burning sugar", which involve the reaction with baking soda instead of sulfuric acid.

Explanation

Concentrated sulfuric acid can perform a dehydration reaction with table sugar. After mixing, the color changes from white to brownish and eventually to black. The expansion of the mixture is the result of vaporization of water and CO2 inside the container. The gases inflate the mixture to form a snake-like shape, and give off a burned sugar smell.[1] The granularity of the sugar can greatly affect the reaction: powdered sugar reacts very quickly but sugar cubes take longer to react.[2]

When sucrose gets dehydrated, heat is given out to the surroundings in an exothermic reaction, while graphite and liquid water are produced by the decomposition of the sugar:[3]

C12H22O11 (s) + H2SO4 (aq) + 1/2 O2 (g) → 11 C (s) + CO2 (g) + 12 H2O (g) + SO2 (g)

As the acid dehydrates the sucrose, the water produced will dilute the sulfuric acid, giving out energy in the form of heat.

C12H22O11 (s) → 12 C (s) + 11 H2O (l)

Alternative experiment

Paranitroaniline can be used instead of sugar.[4] It takes longer time for a black snake to develop and it requires heating under fumehood, but once formed, the black snake rises from the container very rapidly.[5] It may lead to explosion if too much sulfuric acid is used.[6]

See also

References

  1. 1 2 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.
  2. ↑ Don't Try This at Home - 3 - Sulfuric Acid and Sugar
  3. ↑ Roesky, Herbert W. (2007). "Experiment 6: Sugar coal by splitting off water from sugar with sulfuric acid". Spectacular Chemical Experiment. Wiley. p. 17. ISBN 978-3-527-31865-0.
  4. ↑ Summerlin, Lee R.; Ealy, James L. (1988). "Experiment 100: Dehydration of p-Nitroaniline: Sanke and Puff". Chemical Demonstrations: A Sourcebook for Teachers Volume 1 (2nd ed.). American Chemical Society. p. 171. ISBN 978-0-841-21481-1.
  5. ↑ Carbon Snake: demonstrating the dehydration power of concentrated sulfuric acid
  6. ↑ How to make P-Nitroaniline
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