Thursday, February 23, 2012

Demo Show for the Third Grade

My son and I are testing the hydrogen gas.  Nice to end with a bang!

Today I did a demonstration show for my son’s third grade class.  The kids are studying the states of matter in school.  I asked him if he would like me to come in and do some demos for his class about this interesting topic.  He was very excited about the idea, so I set it up with his teacher and here we go.

Water and Ice Balloons
The first thing I did was pass around three balloons; one was filled with air, another was filled with water, and the third was filled with ice.  If you ever want a fun party favor for kids, just throw some water balloons in the freezer.  They were absolutely thrilled by the frozen balloon.  I described to the kids how I made it so they could repeat the experiment at home.  The three balloons provided a nice platform for comparing and contrasting the properties of the three states of matter.

Siphoning the blue water.
Next I turned my attention a common property of liquids and gases:  they both flow.  It’s easy to see how liquids flow and take on the shape of their container, but not as easy to see gases do this.  First I set up a siphon with some blue water to show the kids that water will flow through a tube to the lowest point.  Then I generated some carbon dioxide gas in the same container and tried to siphon it.  I did this demo successfully with my classes about a month ago, so I was confident that I could repeat it here today.  Although we confirmed the presence of carbon dioxide in the source container with a candle, I did not wait long enough for the gas to flow through the tube into the lower container.  I guess the high-energy third graders got the best of me on this one.

Making carbon dioxide
Pour the gas.

The next thing I did was another demo with carbon dioxide gas.  I filled a small fish tank with the gas by dumping a large amount of baking soda in the bottom and then pouring vinegar on top of it.  The kids loved watching the bubbling reaction.  Many kids asked what would happen if I added food coloring to the mixture, so I dropped in some green food coloring.  I think they were disappointed that the bubbles weren’t green.  I tested the carbon dioxide with the candle again to show the kids how much gas we had made.  Then I blew soap bubbles into the tank.  This demo is always a big hit because the soap bubbles hover on the top of the carbon dioxide.  I’m used to doing this for teenagers, who are mildly amused by the whole thing.  But I didn’t think about how excited kids get when they see soap bubbles.  The front row jumped up and started chasing the bubbles and popping them before they went into the tank.  Once I convinced them to let the balloons go into the tank, we got to see the effect.  But, honestly, I think they were more interested in the ones that missed the tank!
Making more carbon dioxide.
The floating bubble trick.

The finale was the electrolysis of water demo.  I wanted to show the kids a chemical reaction that would demonstrate the chemical formula of water.  Once I got the Hoffman appartus set up and going, I let them come up in small groups to look at the reaction going.  I’m not sure that the kids could make the connection between the two to one ration of hydrogen and oxygen gas to the water molecule.  However, I think they all enjoyed seeing the reaction and observing the color changes.  They also got to see the water displacement technique as we trapped the gases at the top of the tubes.  I finished off the day with the pop of the hydrogen gas.  Overall, it was a lot of fun to work with the kids.  I hope that they learned something from my show, but I’m sure that they walked away thinking that science experiments are fun to do.

Here I'm trying to get the third graders to understand that water is 2 parts hydrogen and one part water.  They were mostly interested in the colors, the bubbles, and the water displacement.  I'm okay with that.

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