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    The Power of Tiny Bubbles

    Kids, can you make popcorn kernels dance?  This particular dance will be up and down rather than side to side.  You will need two clear glasses or containers, water, clear soda water, and several uncooked popcorn kernels.  Fill one glass with water and the other with soda water, then drop a few popcorn kernels in each.  Notice whether they sink or float right away.  Then wait a few minutes to see where they are and what they are doing.  Tap the side of the containers and notice what happens.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    The popcorn should sink to the bottom of the water glass and stay there pretty much forever.  As for the soda glass, however, what do you think makes the kernels float after awhile, and what makes them sink again?  This cycle is possible using the power of tiny bubbles.  Bubbles of carbon dioxide, that is.   When enough bubbles stick to the kernels, buoyancy lifts them to the surface.  There, the bubbles burst and the kernels sink again.  Tapping also makes the bubbles come loose.  Your sink-float-sink cycle should last about 1/2-hour before the soda gets too flat.  Do you know another way to make a solution with carbon dioxide bubbles?  Start with water, add some vinegar, then sprinkle in some baking soda, and voila!  The acetic acid (CH3COOH) reacts with the sodium bicarbonate (NaHCO3) to make carbon dioxide gas (CO2), water (H2O), and sodium acetate (NaC2H3O2).

    Previous ChemShorts columns about this activity have appeared; see “Dancing Raisins” 2/92 and “Floaters and Sinkers” 1/93.  The latter suggests items and amounts needed for an impressive large-scale demo.

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    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    kcarrado@anl.gov
    December 2004

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    References:

    52 Amazing Science Experiments” by Lynn Gordon, 1998; Chronicle Books, San Francisco, CA