What You Need:
- Large, tall clear glass jar filled with water—half a gallon or more works best!
- Blue, red and yellow liquid food coloring
- 2 tablespoons cooking oil
- Small jar
- Spoon or stir stick for mixing
- Clear Pyrex measuring cup
What You Do:
- Fill a large clear glass jar—half a gallon or larger—with plain water. Place it on a table where your child can watch it from several angles.
- Invite your child to pour 2 tablespoons of oil into a clear Pyrex measuring cup. (Remember: measuring is a core science and math skill in elementary school, and there’s no such thing as too much practice.)
- Now help your child put in about 5 drops each of red, blue, and yellow food coloring into the oil. Stir each color into the oil.
- Have your child pour the oil onto the water in the jar all at once. At first, the oil will be spread around in globules, but keep watching: right before your eyes, the oil and food coloring will first float to the top, and then the globs will “find” one another and come together.
- Now it’s time for even more fun as the “fireworks” begin! The food coloring will begin to separate from the oil and move back into the water, in long streams of each of the three colors. The colors will separate from one another as if they never mixed in the first place, and stream through the water in the three original colors that you began with. For both adults and kids alike, the results can be mesmerizing.
What's Going On:
This experiment is a demonstration of that old scientific truth: “oil and water don’t mix.” Another important scientific property being demonstrated here is the movement of liquid molecules and the effects of "relative density." Oil molecules like to stick to other oil molecules more than they like to stick to water molecules. Likewise, water molecules are attracted to other water molecules more than they are to oil molecules. Left to their own devices, oil and water will push each other away and try to get as far away from one another as possible.
When you pour the food coloring into the oil and shake it, the two will mix briefly, but the mixture is quite unstable at this point. Then, when you pour the oil onto the water, it will break up at first, but as you continue to watch, you'll see the oil molecules find one another and begin to come back together. Finally, the water-soluble (meaning "water-liking") food coloring finds its way out of the oil, and heads back into the water, one color at a time, offering an extra art lesson in the ways that primary colors combine and separate. In the spirit of adventurous scientists everywhere, you can encourage your child to try this experiment several times, with lots of colors!