Put a Spark in Your Stoichiometry Lesson!

Michelle Okroy recently shared some video resources intended to help students learn about stoichiometry. Also, Chad Husting recently shared a laboratory experiment on stoichiometry that he uses with his students. I thought I'd add to this discussion by sharing one of my favorite chemistry demonstrations that I use when teaching stoichiometry. The reaction used in this demonstration is the oxidation of iron wool:

x Fe (s) + y (1/2 O2) (g) --> FexOy (s)

Steel wool is burned. After this, the ratio of iron to oxygen in the resulting compound is determined. This demonstration is very simple to carry out. All you need is some fine steel wool, a beaker, a hair dryer, a lighter, and a balance. The demonstration and accompanying lesson can be seen in the video below:

It is interesting to note that the iron oxide produced is a non-stoichiometric compound. That is, the ratio of iron to oxygen in the product is not a whole number ratio. You can learn more about non-stoichiometric compounds in this article.This demonstration on the oxidation of iron using steel wool can be made even more dramatic if it is performed outside at night in the following way: A large piece of steel wool is attached to a very long string or stainless steel wire. The wool is ignited using a lighter or a 9V battery. Holding the end of the string, the ignited steel wool is rapidly swung overhead. (CAUTION: This experiment generates a lot of sparks. The skin of the person swinging the ignited wool overhead should be completely covered. Wear heavy gloves, a hat, a heavy coat, long pants, close-toed shoes, and eye/face protection. Observers should be at least 30 feet away from the person swinging the steel wool). The resulting display of sparks is quite beautiful:

Let me know if you try either of these experiments. I look forward to hearing from you!

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Comments 1

Doug Ragan's picture
Doug Ragan | Tue, 05/03/2016 - 10:12

Thanks Tom for making the video and explaining this so well.  I can now give a much better explanation when the rust ratio problem comes up regarding oxidation numers, etc.  Some iron +2 and some +3.