[neact] Re: potassium chlorate and gummi bear
- From: "Sue Klemmer" <Sue_Klemmer@xxxxxxxxxxxxx>
- To: neact@xxxxxxxxxxxxx
- Date: Mon, 05 Jan 2009 11:46:52 -0500
Here's a live demo that's a bit less hazardous.
I do this with plain paper and sodium chlorate. I put the NaClO3 in a
small evaporating dish on a hotplate in the hood. I have several
half-sheets of paper handy. First, outside the hood and over a sink I
light one piece of paper on fire with a match, and while they watch it
burn we review ideas about combustion: esp. the idea that oxygen is
usually the limiting reagent when burning paper, hence the ash residue.
Then I take another piece of paper, crumple it into a ball, and drop it in
the dish of melted (and decomposing) sodium chlorate. The paper ignites
rapidly (hold it down with tongs or a glass stirring rod) and burns
brightly and completely to carbon dioxide and water vapor. A hefty
tablespoon of NaClO3 will let you burn one piece of paper - I usually put
in enough to get 2-3 pieces burned. When the sodium chlorate has fully
decomposed, the next piece of paper you put in the evaporating dish burns
"normally" to ash. (That way you know all the chlorate has decomposed.)
While the gummi bears are a more spectacular event , I like the paper
because of its familiarity to students (and easy cleanup). They are less
likely to think there's something "magical" sheets of paper than in gummi
bears. You can then connect this to other oxygen-enriched or environments
(why do you blow on a fire? why do oxyacetylene torches have an oxygen
supply? why is it so often a fatal fire when people smoke around an oxygen
tank? why do athletes do blood-doping?) In addition to the videos
mentioned before, you can follow up with the 1 minute clip from October
Sky (where they dump KClO3 down the sink in the lab and someone else ads a
spent match) or the old 25 minute Film for The Humanities "Explosion on
the Lady Delia".
Susan A. Klemmer
Chair, Science Department
Camden Hills Regional High School
25 Keelson Drive, Rockport, ME 04856
PS It wasn't clear whether this demo was about combustion or energy. If
you're into the energy concept, here's another favorite demo that's not
very hazardous to do but memorable to students and takes under 5 minutes.
Get a small bag of baked potato chips and a bag of cheap fried ones
(cheaper the better). Hold a baked chip in a bunsen burner flame with
tongs and note how it burns. Then burn a fried chip: it burns brighter and
faster, and will often drip burning fat. Ask the class to tell you why
they burn differently - and have them check the caloric contents on the
bag.
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