Kids, if you just add food coloring to milk, not a whole lot happens. However, it only takes one simple ingredient to turn the milk into a swirling color wheel. Here is what you do.
Materials:
- 2% or whole milk
- food coloring
- dishwashing liquid
- cotton swab
- plate
Instructions:
- Pour enough milk onto a plate to cover the bottom.
- Drop food coloring onto the milk. Watch a video (see reference below) so you can see what to expect.
- Dip a cotton swab in dishwashing detergent liquid.
- Touch the detergent-coated cotton swab into the milk in the center of the plate.
- Don't stir the milk; it isn't necessary. The colors will swirl on their own as soon as the detergent contacts the milk.
How It Works:
Milk consists of a lot of different types of molecules, including fat, protein, sugars, vitamins, and minerals. If you had just touched a clean cotton swab to the milk (try it!), not much would have happened. The cotton is an absorbent, so you would have created a current in the milk, but you wouldn't have seen anything especially dramatic happen.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
When you introduce detergent to the milk, several things happen at once. The detergent lowers the surface tension of the liquid so that the food coloring is free to flow throughout the milk. The detergent reacts with the protein in the milk, altering the shape of those molecules and setting them in motion. There is also a reaction between the detergent and the fat in the milk. This, by the way, is how detergent helps lift grease off dirty dishes. During the reaction, the colorful molecules in the food coloring get pushed around. Eventually equilibrium is reached, but the swirling of the colors continues for a while before stopping.
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References:
Anne Marie Helmenstine, About.com Chemistry,
http://chemistry.about.com/od/chemistryhowtoguide/a/magicmilk.htm
http://www.youtube.com/watch?v=lf4HHazghGs
