Oil and Water Don’t Mix!

Oil and water are both liquids, but they are very different substances. Because of their chemical composition, they do not like each other. Oils of all kinds--cooking oil, motor oil, light machine oil--have long chains of carbon atoms with hydrogen atoms attached to them. You probably know that water is two atoms of hydrogen attached to one oxygen atom. The molecules of oil are attracted to each other and repelled by the water molecules. Try these experiments to see how water and oil react. You can even write secret messages that only a friend who knows the trick can read.

For the first experiment, you need a small, clear drinking glass or glass jar, a measuring cup, liquid cooking oil, water, food coloring (any color), a tiny bit of margarine (stick margarine works best), some old crayons and a sharp knife. Also, like every scientist, you should write down your observations in a notebook.

Measure one-fourth cup of cooking oil into the drinking glass or jar. Add one-fourth cup of water and watch what happens. The oil and water molecules push away from each other and cling to their own kind. The oil is less dense (weighs less) than the water, so it floats above the water.

Next, add about five drops of food coloring to the mixture in the glass, stir and wait a few minutes. With the sharp knife, scrape tiny shavings off the crayons (choose a color that is different than the food coloring). Drop the shavings on top of the liquid in the glass. Get a small dab of margarine and roll it in your hands to make a ball. Drop the ball into the glass. Watch what happens to each item that you add.

Food coloring has water in it, so the drops go to the water layer. The crayon shavings and the margarine are both more like the oil, so they stay in the oil layer.

You can use the reaction of oil and water to write secret messages. You will need white paper, a white candle or white crayon and watercolor paints. Write a message with the candle or crayon on the paper. It will be difficult because your writing will be invisible. Next, paint over the paper with any color of the watercolor paints. Your message will appear!

This trick works because the wax from the candle or crayon is an oil compound. Watercolor paint has water in it, so it pulls away from the oil-based writing and colors the paper so your message appears.

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