• Safety with Chemical Demonstrations

 

 

Safety with Chemical Demonstrations

Learning is a multisensory process, especially in the physical sciences. Students must experience science through active participation, not just by sitting through an instructor monologue. While this author strongly encourages the use of demonstrations and hands-on activities in the classroom, safety for working with chemicals of all kinds is imperative. (See the Compleat Chymical Demonstrator.)

Demonstrations and activities are an essential part of active learning. A recent report has confirmed that students get better grades and fail less when professors use active-learning methods in the classroom (Proc. Natl. Acad. Sci. USA 2014, DOI: 10.1073/pnas.1319030111). This author, however, has experienced students, at all levels, around the world, who never experienced demonstrations and/or hands-on activities in their academic career.

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Safety With Chemical Demonstrations

Chemical Demonstrations: The good, the bad, and the ugly - This describes a number of accidents that occurred with chemical demonstrations, dangerous demonstrations, limits of published demonstration guidelines, and recommendations and procedures for safer demonstrations. Yes, you can do a Rainbow Flame Demonstration. (This was previously presented, in part, as an oral paper at the 251st ACS National Meeting, San Diego, CA, in 2016.) Author's Note: Some of the references in this paper are YouTube or other videos as opposed to articles about accidents. It is the belief of this author that more knowledge is gained by actually observing the poor procedure or accident.

Elephant's Toothpaste has been a popular demonstration for many years. It is not without safety concerns. An attempt was made to create a "world record" for the largest Elephant's Toothpaste reaction. A tale of 2 explosions by Melissa Gilden describes this reaction. The original article can be found at https://cen.acs.org/safety/A-tale-of-2-explosions/98/i8

Nick Uhas explains how he did this in an 11 minute video at https://www.insider.com/youtuber-nick-uhas-foam-explosion-experiment-david-dobrik-clean-up-2019-12 Luckily, no one was directly injured in this "experiment". My comments on this follow below.

More on Elephant's Toothpaste. In making a "world's record" elephant's toothpaste, the experimenter claims that he and colleagues calculated how much of each component would be needed.  To scale up any reaction from "laboratory size" to any large size requires more than just a stoichiometric reaction calculation.  Reations do not scale up in a linear manner.  This is where a chemical engineer is needed, along with pilot plant studies.  Furthermore, these experimenters scaled up the amount of potassium iodide "catalyst" - another unknown. Scaling up does not necessarily require an equivalent quantity of catalyst.  Potassium iodide is not a true catalyst in this reaction.  In the case of the potassium iodide, oxidation of the iodide ion occurred, thus yellow stains of iodine on surrounding structures. Those stains lasted for days as the iodine sublimed into the air producing topic vapors to individuals in the area. This is why books, YouTube videos, TV shows, and others showing "fantastic" demonstrations are dangerous to individuals with little or no knowledge of the chemistry involved.  The sources may state "Do not try this at home.", but, in my opinion, it is viewed as a challenge to uninformed individuals.

Reference and background information:

The Art of Effective Demonstrations

The First Day

Science Demonstrations, Experiments, and Resources: A Reference List for Elementary through College Teachers Emphasizing Chemistry with some Physics and Life Science

Common Chemicals and Supplies in and Around Your Home - Includes a table of mass-volume equivalents for selected chemicals.

Safer alternatives to fire and explosions in classroom demonstrations by David A. Katz. Published in the Journal of Hazardous Materials, 36 (1994) 149-158.

Internet Sources for Chemistry Demonstrations:

At this time, Tested Demonstrations in Chemistry by Hubert Alyea and Frederic Dutton, is not available as an ebook on the Internet. This is the classic book on chemical demonstrations, compiled from the Journal of Chemical Education, however there are a lot of safety issues with many of the demonstrations. Used editions may be available from booksellers.

Tested Demonstrations in Chemistry, the revised and udated version by George Gilbert, is not available as an ebook on the Internet. George Gilbert combined and updated many of the demonstrations in the original book by Alyea and Dutton and removed many of the hazardous procedures. Used editions may be available from booksellers.

Classic Chemical Demonstrations 100 chemistry demonstration from the Royal society of Chemistry

Chemical Demonstration Booklet prepared by Magda Wajrak, school of Natuaral Sciences, Edith Cowan University