Friday, October 21, 2011

Demo Show for Pack 26

This week I gave a demo show for my sons’ Cub Scout Pack. 

Pouring carbon dioxide onto a candle.
I started off the show with the Genie in a Bottle trick, a ChemFax by Flinn Scientific (Publication No. 91200).  I wrapped a 2-liter plastic bottle in aluminum foil to make the Genie’s bottle.  The “Genie” was a reaction of 30% hydrogen peroxide and sodium iodide, the catalyst in the decomposition reaction of hydrogen peroxide that produces water and heat.  The sodium iodide crystals were suspended in a small sack at the top of the bottle held in place by a rubber stopper.  When I took the stopper off the bottle, the Genie escaped in a big puff of steam, and left behind a shrunken plastic bottle. 

For my second demo, I asked one of the Tiger Cubs to come up and fill up a beaker with Styrofoam packing peanuts.  The peanuts “disappeared” as fast as he could put them into the beaker.  I encouraged him to try harder, but the peanuts kept shrinking before his eyes.  What he didn’t know is that I had poured some acetone, a clear and colorless organic solvent, into the beaker before the show.  The small amount of acetone quickly dissolved the packing peanuts as he dropped them in the beaker.

 Blue water for displacement.

Next I did a water displacement demonstration with baking soda and vinegar, one of the many reactions that produce carbon dioxide gas.  I like doing this demo for kids because it’s a different look at the classic “volcano reaction”.  Taking the advice of Dr. Shakhashiri, I used large apparatus to make the reaction visible to the audience.  I collected the gas in a 2-liter bottle, using a 5-gallon fish tank for the water displacement.  I had a volunteer mark the water level on the tank before the reaction so we could see any change.  I put food coloring in the water in the bottle so there was another visible change for the kids to observe during the demo.  Once we filled the bottle with carbon dioxide gas, I used it to put out a candle.  I love to show kids that gases can pour, even when we can’t see them.

Heating the water in the can.

Ready to flip it into the ice water bath.
The finale was the classic “Can Crushing Demo”.  I heated a small amount of water in an empty soda can until steam was visible.  I quickly inverted the can in an ice water bath.  The can crushed with a shocking smash.   I learned how to do this demo during my summer workshop at Longwood College.  I was hooked on chemistry demos after performing this one for my class that fall.

The can crushed in the ice water.

Thanks to Pack 26 for inviting me for a fun night of science.

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