Demistry of candles and flames

Girl standing behind candles.As a high school student taking chemistry for the first time, I remember that we were given a white candle and told to make as many observations as possible during a class period. After being told that over one hundred observations were possible, and having less than twenty observations, we looked ahead to chemistry with dread, knowing that we were poor observers. As a teacher watching my first class bore through the same exercise, the thought of “Why go through this pointless exercise?” raced about in my head. Then my wife took up candle making as a hobby.

The real point of the exercise is to teach students how and what to observe. So the next year, out of a large paper bag a candle was drawn and handed to each student, but not identical white candles. Candles of different colours, even a candle layered in the colours of the rainbow; candles of varying scents, and unscented candles, candles of varying size and shape, candles of beeswax, candles of paraffin “wax”, hardened with different amounts of stearic acid, including almost pure stearic acid, were used. The idea was to have no two candles the same.

Immediate observations to make flowed into the students’ minds as they compared candles. There were complainers as usual in such situations, “Why isn’t my candle scented?” “It’s not your candle, you’re only borrowing it.” The better students even compared candles quantitatively, asking, “Which candle is largest?” measuring length, diameters and masses.

Since the wax composition was different, flames also differed. “What colours are observed in a candle flame?” “How do the flames differ?” were questions asked.

No one managed to get over one hundred observations, but the exercise was more enjoyable and during the post-lab discussions students could easily list various properties that could be observed.

(The author has no stocks in any candle company.)

(This is a reprint from Chem 13 News, October 1985. When this was written Andy was a graduate student at the University of Waterloo. He is now about to retire from Stouffville District Secondary School, Stouffville ON.)

Andy is organizing the Generations symposium at ChemEd 2013 next summer at the University of Waterloo, Waterloo ON.  The idea behind the symposium is for experienced presenters to work as a team with less experienced presenters. Past Generations symposiums have had over 20 teams presenting favourite demos, teaching tips and humorous ideas for the classroom.

Contact Andy Cherkas, to participate.