Misconceptions in the Exploding Flask Demonstration Resolved through Students’ Critical Thinking

Abstract

As it connects to a large set of important fundamental ideas in chemistry and analytical techniques discussed in high school chemistry curricula, we review the exploding flask demonstration. In this demonstration, methanol vapor is catalytically oxidized by a Pt wire catalyst in an open container. The exothermicity of reactions occurring at the catalytic surface heats the metal to the extent that it glows. When restricting reactant and product gas flow, conditions may favor repetitive occurrence of a small explosion. We show how mass spectrometry and infrared spectroscopy allow for unravelling the chemical background of this demonstration and discuss various ideas on how to use it in a classroom setting to engage students’ critical thinking about chemical research. Along the way, we show that two commonly published ideas about the chemical background of this demonstration are incorrect, and we suggest simple tests that may be performed in a high school setting either as an addition to the demonstration or as a student research project.

Heterogeneous Catalytic Oxidation of Ammonia by Various Transition Metals

“…Using a flame or a power supply, we heat various transition metal catalysts in a standardized setup, resulting in a remarkably practical demonstration experiment that can be used to initiate discussion on many aspects of heterogeneous catalysis. The demonstration is complementary to heterogeneous catalytic oxidation of alcohols, reported by our group earlier in this Journal, 5,6 and well-suited to expand upon the topic.…”

“…This was recently attributed to the efficient dehydrogenation of methanol with recombinative hydrogen desorption leading to a buildup of an explosive hydrogen–oxygen mixture in the flask. 6…”

“…This was recently attributed to the efficient dehydrogenation of methanol with recombinative hydrogen desorption leading to a buildup of an explosive hydrogen−oxygen mixture in the flask. 6 Whereas the "exploding flask" demonstration illustrates heterogeneous catalysis and provides a means to introduce catalytic activity, the oxidation of ammonia is a better starting point to discuss catalytic selectivity. As mentioned in previous reports of demonstration experiments on this topic, 7−15 the following reaction equations describe the possible chemical conversions associated with the oxidation of ammonia: Reaction 1 describes the first step of the Ostwald process for the production of nitric acid (HNO 3 ), the main raw material for fertilizers.…”

“…A visually attractive lecture demonstration of heterogeneous catalysis is the “exploding flask” experiment. − A glowing wire of an appropriate transition metal is placed in a flask containing a layer of methanol. The wire continues to glow, providing evidence of an exothermic reaction occurring at the catalytic surface.…”

Replacement Of Conceptions Developed During Health Professions Education

“…"The general consensus among education researchers during this time was that students' misconceptions were so prevalent that instruction needed to focus on revealing, confronting, and replacing them" 5 . "Constructivism asserts that prior knowledge is the primary resource for acquiring new knowledge, but misconceptions research has failed to provide any account of productive prior ideas for learning expert concepts and has overemphasized the discontinuity between novice and expert" 6 .…”