Saturday, January 21, 2012

Yet another reason why I do demos

Sharing the fun of chemistry at home!
I received these photos from a parent of one of my students.  She has two daughters, one who is in my chemistry class this year and another who took my class two years ago.  In the photos you can see the younger sister showing her older sister a fun demo I did in class just before Christmas vacation.  It made my day to see the girls sharing the excitement of chemistry with each other (without me telling them how exciting it is) and with their parents while on school vacation.  It just doesn't get better than that for a science teacher.

Dipping the dollar bill in the liquid.
Who gets to light it this time?
In the demo I dip a dollar bill in a clear, colorless liquid and then light it on fire.  The bill appears to be engulfed in flames, but it quickly burns out and the money is left unharmed.  "What?!  How did you do that?  Do it again!" my students exclaim when they see the money burn.  After I repeat the demo a few more times, I give them the explanation.  It's simple, the liquid is half rubbing alcohol and half water.  The flammability of the alcohol creates the impressive flames, but the high heat capacity of water keeps the dollar bill from being damaged.  When I'm working with household products I usually say the Myth Busters line, "Kids, don't try any of these demos at home, I'm what they call an expert."  But maybe this time I said, "This one is so easy you can do it home and impress your family."  That sounds like something I would say.  Anyway, the girls took my advice and did the demo at home.  You can too, in a well ventilated area, next to the sink, with your hair tied back, and safety goggles on if you have them!  Enjoy.

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