Celebrate March with this crafty, rainbow-of-colors experiment. All you need are a few things you probably already have in your kitchen.
Plate with high rims
Liquid food coloring (not gel)
Dish soap (Dawn works well)
Cotton swab or pipe cleaner
Pour enough milk into the plate to completely cover the bottom.
Add drops of food coloring into the milk. Make sure to include some in the center. Don’t go crazy at first; make sure there is still plenty of white.
Dip the dry end of the cotton swab in the center. What happened?
Now dunk the end of a cotton swab in dish soap and place the soap drenched cotton swab in the center of the milk. Now what happened?
Alternate method: Don’t even bother with the cotton swab. Drip a few drops of dish soap directly in the center of the plate.
How does it work?
Milk is a solution. That’s a fancy way of saying it’s made up of many parts – mostly water with vitamins, minerals, proteins, and fat droplets.
Soap on the other hand is made of up of bipolar molecules, literally! One side of soap is water- loving (hydrophilic) and the other side is water-hating (hydrophobic). The water-hating side loves oil and fat and so it grabs onto, or bonds, with the fat molecules in the milk. The molecules of fat bend, twist and roll around to match up, all the while everything else – water, food coloring, etc. – is getting bumped and shoved out of the way. This is what makes the colors look like they are dancing.
As the soap becomes evenly mixed with the milk, the action slows down and eventually stops. This is why milk with higher fat content creates a greater burst of color. There are more fat droplets to connect with.
Take the experiment further
What do you think would happen if you add more soap after the initial color explosion? How would this experiment work with 2%, 1%, or skim milk? How about with water? Can you see the fat/soap race better with more food coloring or less? Don’t forget to try different patterns and colors!