Fireworks are fabulous! We love watching the colors explode and gently float down through the air, but we can’t watch fireworks all the time. Underwater fireworks are something we can watch any time, even in our kitchen!
The Experiment
Supplies: Water, vegetable oil, food coloring (any color), a large clear glass, a second smaller glass, a fork
What to do: Fill the large glass almost to the top with room-temperature water. Pour 2 tablespoons of oil into the other glass. Add 2 drops of food coloring to the glass with the oil. Vigorously stir the oil into the food coloring using a fork. Stop once you break the food coloring into little drops. Pour the oil and coloring mixture into the tall glass. Now watch! The food coloring will slowly sink in the glass, with each droplet expanding outwards as it falls.
What is happening: Food coloring dissolves in water, but not in oil. This has to do with the incompatibility of the molecular structures of the water and the oil. When you pour in the food coloring/oil mixture, the oil will float at the top of the water because it is less dense. The food coloring will begin to dissolve once it sinks through the oil and into the water.
Take It Further
Variations on this demonstration:
- Try mixing in one drop each of two different food colorings.
- What happens if you omit the oil and drop the food coloring directly into the water?
- Try varying the size or shape of the water glass, the amount of the oil, or the amount of the food coloring. Just remember, when you are manipulating variables to only change one thing at a time!
Links
For a more detailed explanation of the miscibility of fluids, along with a more expansive version of this demonstration, head over to the Scientific American website.