While serious accidents causing catastrophic injury in high school science activities are rare, when they occur their human toll can be devastating. This post examines one potentially dangerous demo, its hazards and suggestions for safer alternatives.
The Rainbow Flame Demonstration:
Several of the most serious science accidents have resulted from the combustion of flammable liquids in teacher demonstrations like the rainbow flame demonstration. In this demo, metals salts are heated in a ceramic dish containing burning methanol. The flame colour observed is characteristic of the metal. Click on this link for an example of how this demo is sometimes done. Please note that the procedure used in this video, in our opinion, is unsafe, inappropriate for students of any age and NOT recommended for teachers.
Methanol vapours are extremely flammable. Furthermore, since the density of methanol is greater than that or air, methanol vapour can flow invisibly across surfaces like the demonstration desk and onto the floor towards unsuspecting observers. A flame, spark or even a hot surface can supply sufficient energy to ignite the vapour and create a sudden flash fire. The situation can be even more catastrophic if a nearby open container of methanol is present.
The Safer (and Better) Way:
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Demonstrations are an integral part of any science program. These activities engage students and help bring the “real world” into the classroom. STAO has recently developed a collection of safe demonstrations/activities for grades 9 and 10 that have been designed to challenge students’ thinking as well as initiate lively classroom discussions that support constructivist learning. These short demonstrations/activities often involve discrepant events related to the topic of focus in the grades 9 and 10 science curriculum, that may surprise students and that can be observed and/or investigated safely by students in the classroom. These demonstrations/activities are available for free download at http://stao.ca/res2/demoover.php
Elephant Toothpaste is a popular demonstration to introduce the concept of decomposition reactions. The chemical reaction involved is the decomposition of hydrogen peroxide into oxygen gas and water. The reaction is very slow at room temperature. Consequently, it requires a catalyst. Manganese dioxide is commonly used to catalyse the reaction. However, bakers yeast works just as well, is easier to clean-up and is non-toxic. The key ingredient for this demo is hydrogen peroxide which is readily available in 6% and 30% solutions. How can you tell whether or not these chemicals are safe to use? Fortunately, most chemicals used in schools come with a HMIS hazard rating. Continue reading