You will need several empty containers, some for liquids and others for materials that are not liquids, such as gravel, cornstarch and sand. Discuss what a liquid is. It can change its shape to that of any container it is placed in. Ask the students to explore the containers with liquids and non-liquids by pouring them into the empty containers. What are their conclusions about the materials? Have any of them been fooled by the cornstarch, because it took the shape of its container? Discuss with them that the cornstarch is not a liquid, but instead is a large group of tiny solid materials.
This activity is called the Invisible Fire Extinguisher. You will need a candle, a plastic coat hanger, matches and two plastic 2-liter bottles, cleaned and with the labels removed. Fashion the wire coat hanger so that one end wraps around the candle, and you are able to dip the candle, wick up, to the bottom of the bottles. Fill one bottle with a cup of vinegar. Light the candle. Lower it into the empty bottle so the students can see that the bottle itself has nothing to do with the results. Place 1 tsp. of baking soda into the vinegar, and lower the candle slowly toward the mixture. The carbon dioxide released when the baking soda and vinegar react will put the candle out.
Begin this activity with a discussion of solids. They generally resist change to their form and have a defined shape and mass. Supply students with an array of solid materials, such as pebbles, crystals, coins and foam. Allow them to pinch and prod the items with their hands and even to use small mallets (if available) on them. Discuss how each item has a definite form and that even pieces such as the foam return to their original form once the experiment is over.
Once your students have studied all three states of matter, use water to round off the unit. Because water can be observed in nature as liquid, solid and gas, it makes a great subject for a culminating project on the states of matter. Simply allow your students to explore and even play with water as a liquid, then pop it into a freezer and watch it become a solid, and finally place it over a Bunsen burner and watch as it turns to steam and then disappears as water vapor. Place a piece of foil or plastic over your boiling water to allow the vapor to condense and become a liquid again.