See what goes down when oil and water don’t mix.
What You’ll Need
vegetable oil
mug or cup
red and blue food coloring
clear glass of water
What to Do
Pour a tablespoon of vegetable oil into the mug.
Add two drops each of red and blue food coloring.
Stir until the food coloring breaks up into tiny droplets.
Pour the mixture of oil and food coloring into the glass of water.
Watch what happens!
How It Works
Is this what you saw? At first, a layer of oil full of colored droplets floated on top of the water. After a few moments, the colored droplets began to sink into the water, making streaks of color.
Two ideas are at work in this activity. The first idea is that water does not mix well with oil. When you stir drops of food coloring into the oil, the food coloring breaks into droplets because it is made up mostly of water and cannot dissolve into the oil. When you pour the mixture into the water, the oil mixture stays separate from the water for the same reason.
The second idea is that water is denser than oil. (A cup of water weighs more than a cup of oil.) That’s why the mixture of oil and food coloring floats on the water. The droplets of food coloring are also denser than the oil. They sink to the bottom of the oil layer. As each droplet touches the water, it begins to mix into the water, flowing downward and making a streak of color.
