Can oil and water mix? Is toothpaste a soild or a liquid?

Today we did an experiment with two liquids. Our big question was....does oil and water mix? Over half of the class said yes they would because other liquids mix together. A few students said it would not mix.

We brought in a vase and filled it with oil. Then we dropped a bunch of colored ice cubes on top. As they started to melt, we saw little drops of the water move through the oil. As they fell to the bottom of the vase, they never mixed into the oil. Students were amazed that they didn't mix in. Once all the ice melted, we were able to see that oil stays on the top and water goes to the bottom. We reviewed the word dense as a class. Students remembered when they put different solids in water they would sink and that the solids were more dense. They quickly figured out that oil is less dense than water and water is more dense and that is why it sunk to the bottom. This was such a fun activity and the students enjoyed watching the water bubble to the bottom of the vase.

We did a second experiment with toothpaste. I asked them if toothpaste is a solid or a liquid. It was about half and half again. I asked them what happens when they put toothpaste on their toothbrush and what happens once we start brushing. Many students realized that toothpaste is both a solid and a liquid. We discussed things that hold shape are called a solid and things that hold the shape of what they are in are called liquids. We realized that somethings can be both and that some solids can change from liquid to solid and back to liquid.