solid, liquid, gas

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Home : 2001 : November : 13

solid, liquid, gas
By Julianne

I start out by talking about molecules and atoms and how they make up everything in the world. We name things made of atoms - tables, people, water, air. Then we talk about how the molecules and atoms are always moving.
Sometimes they are packed tightly together and can move very little. I have the kids get up and be molecules. (I mark a 3 foot circle on the floor with masking tape before we start.) They cluster close together and jiggle. I call out "stop" and ask them to look at where they are standing. How heavy do you think the circle is right now? This is how a solid acts. It is usually pretty

heavy because the molecules are packed so close together. Now we "heat things up" by having the kids move a little more. As they move apart I call "stop" once more. Now how heavy is the circle? It is lighter because there are less people (molecules) standing there, just as a liquid is usually less dense than a solid. Now we really move! I call "stop" once more and again we look at the circle. Usually there's only one person in it at this point. It's really light, just like a gas. Now we're ready to look at the real things. Here are a couple of experiments you can do with your students.

1. Have students fill a jar with some pebbles, some water and leave some room at the top for some air. Put the lid on the jar and shake it up. Now put it down and watch what happens. Where do the solid items go? Why? Where does the liquid go? What about the gas?

2. Pour different liquids into a glass to show that they have different densities. Start with corn syrup which is pretty dense. On top of that add colored water. On top of that add cooking oil, then add a layer of colored rubbing alcohol. (Be sure no one tries to drink this!) If you are careful pouring in your layers they should stay fairly separate. (Oh, gosh, I've forgotten if the oil or the alcohol goes on top. Try it before you do it with the kids!)

3. Take a large spoon and place an ice cube in it. Have the students name it as a solid and name some other solids. Now melt it over a candle flame. Now it is a liquid. Did the material itself change, or just its form? Let the liquid begin to boil and change again into a gas. Where does it go? How do you know? Could you devise an experiment to prove your theory? How could you get the water molecules back into a liquid or a solid? Have the kids brainstorm ways.

4. Other things you can melt over candle flame (be VERY VERY careful. I have never set a school on fire - but it wouldn't be a pretty sight.): sugar, sulphur powder (available in many pharmacies), candle wax. Actually, candle wax burns as a gas, not a liquid as you might expect. You can prove this by making a little "chimney" out of aluminum foil. I wrap several layers of foil around a pencil to make a tube about the diameter of a straw and about 2 inches long. Now hold it with pliers at the base of a burning candle. When you begin to see smoke come out of your chimney carefully hold a lighted match to the top of the chimney. You should be able to get a flame to burn there when you take the match away, much like a pilot light in a furnace. It is burning the gaseous candle wax.

Have fun with your unit.