We find that the procedure for “Sugar Dehydration without Sulfuric Acid: No More Choking Fumes in the Classroom!” (1), which calls for igniting a reaction mixture of 25 g sugar, 12 mL ethanol, and 5 g KClO3 on a watch glass resting upon paper toweling, can lead to watch glass breakage and thereby a fire hazard. The watch glass breakage occurs through high temperature gradients generated by the exothermic reaction of KClO3 with sugar. Once the watch glass breaks, the reaction mixture can ignite the paper toweling.
The demonstration, which combines an irreversible sugar dehydration reaction with an irreversible oxidation reaction, can be effectively and safely performed in a 3 in. clay flowerpot partially filled with sand and suspended from a ring-stand with a 3 in. iron ring. Filter paper placed over the drainage hole of the clay flowerpot prevents sand from leaking out. A large collection vessel, such as an iron pail or porcelain dish, set immediately below the flowerpot provides an extra measure of safety and collects any reaction products that leave the flowerpot.
Further, we found that burning ethanol- or isopropanol-soaked sugar in the absence of KClO3 leads to a carbonaceous product similar to that reported in ref 1 as “small black upwellings of carbon” and “that smells for the most part like burnt sugar” and discussed in ref 2. This modification demonstrates sugar dehydration without the use of KClO3. Therefore, disposal of any unreacted and unstable sugar–KClO3 mixture (1) is no longer a problem.
With our flowerpot demonstration setup, it was easy and safe to perform and contain the traditional, colorful, and highly exothermic sugar oxidation by KClO3 demonstration (3). Because of the large volume of hot gases released as well as the observation that KClO3 oxidation of sugar in the presence of sulfuric acid may yield toxic and reactive gases Cl2, ClO, and ClO2 (1, 3), we recommend performing this demonstration in a fume hood. To well mixed stoichiometric amounts of sugar (~1 g) and KClO3 (~3 g), we instantaneously (~1 s) initiated the reaction with a drop (~0.05 mL) of concentrated sulfuric acid. An alternative procedure, using a match to ignite an ethanol saturated reaction mixture, gives a one- to two-minute delay before initiating the highly exothermic sugar oxidation reaction.
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