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 dehydration reaction with table sugar. After mixing all compartments, the color change progresses while stirring the mixture from white (nature) to be more brownish and eventually to black mixture. The expansion of the mixture is the result of vaporization of water and CO2 inside the container under the mixture where it bloats up the mixture to form snake-like shape and burned sugar smell.[1] Granularity of sugar can greatly affect the reaction. Powered sugar reacts very quickly but sugar cubes take longer time to react.[2]

Chemical explanation

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

When sucrose gets dehydrated, heat is given out to the surrounding, an exothermic reaction, as well as the production of graphite and liquid water, which shows the decomposition of the sugar:[3]

C12H22O11 (s) → 12 C (s) + 11 H2O (l)

As the acid dehydrates sucrose, it gives out water as a product which will dilute the sulfuric acid itself and therefore gives out energy in the form of heat.

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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