Letter pubs.acs.org/jchemeduc
A Modification of the Combustion of Diamonds Demonstration Ben Ruekberg* Department of Chemistry, University of Rhode Island, Kingston, Rhode Island 02881, United States ABSTRACT: The demonstration of burning diamonds and reducing the combustion product to graphite lacks a control experiment. An additional experiment is suggested. KEYWORDS: Elementary/Middle School Science, High School/Introductory Chemistry, Demonstrations, Hands-On Learning/Manipulatives, Public Understanding/Outreach, Oxidation/Reduction
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he demonstration suggested in “Classroom Demonstration: Combustion of Diamond to Carbon Dioxide Followed by Reduction to Graphite”1 would be improved by the addition of a control experiment. The demonstration presented by Miyauchi and Kamata has two steps: the oxidation of diamond,
T
C(diamond) + O2 (g) → Co2(g)
REFERENCES
(1) Miyauchi, T.; Kamata, M. J. Chem. Educ. 2012, 89, 1050 −1052.
(1)
Followed by the reduction of carbon dioxide, 2Mg(s) + CO2 (g) → 2MgO(s) + C(graphite)
(2)
Although a carbon product appears after the reduction step, the audience has no way of knowing that this product does not normally occur when magnesium is combusted. To disprove this possibility, a control experiment is suggested. If two flasks are available, after the oxidation of the diamond, a second flask is purged with oxygen, as in the oxidation step, and fitted with an identical reduction apparatus containing the magnesium ribbon to be the control, and both magnesium ribbons can be ignited simultaneously. If only one flask is available, this control experiment can be performed first on the oxygen-filled flask, according to the instructions of the reduction experiment, or an equal length of magnesium can simply be burned in air and the combustion product examined in the same way as the product of the carbon dioxide reduction reaction. As the authors suggested, the audience should be warned against looking at the ignited magnesium. The apparatus with carbon dioxide will produce the carbon product (eq 2) and the apparatus with pure oxygen will not: 2Mg(s) + O2 (g) → 2MgO(s)
(3)
Instead, a white powder is produced. This result shows that the black material came from the gas produced by the burning of the diamond and not the oxygen or the magnesium. Further, it demonstrates the importance of doing control experiments. I would suggest that the authors consider this small modification.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest. © 2012 American Chemical Society and Division of Chemical Education, Inc.
Published: December 7, 2012 10
dx.doi.org/10.1021/ed300363h | J. Chem. Educ. 2013, 90, 10−10
