Here’s what you need:
- Milk (whole or half-and-half—skim won’t work)
- A tray or shallow bowl
- Food coloring
- Cotton swabs
- Liquid dish soap (Dawn works well)
Here’s what to do:
Pour some milk into your tray. You'll want it at least 1/4" deep. Add several drops of food coloring near the center of the tray. Dip a cotton swab into the color (don't stir it, just dip!). Nothing really happens.
Now, dip your cotton swab into your liquid dish soap and then dip back into your milk. (Again, don't stir, just dip it in and hold it in place for a few seconds!) Watch how the colors "jump" away from the soap, and then begin swirling around on their own!
For older kids, under the supervision of an adult, allow the kids to perform the experiment themselves. Before they start, ask for their hypothesis of what they think will happen.
For younger kids, the adult will need to set up the experiment and perform as necessary.
How Does It Work?
"Milk is mostly water but it also contains vitamins, minerals, proteins, and tiny droplets of fat suspended in solution. Fats and proteins are sensitive to changes in the surrounding solution (the milk).
"The secret of the bursting colors is the chemistry of that tiny drop of soap. Dish soap, because of its bipolar characteristics (nonpolar on one end and polar on the other), weakens the chemical bonds that hold the proteins and fats in solution. The soap’s polar, or hydrophilic (water-loving), end dissolves in water, and its hydrophobic (water-fearing) end attaches to a fat globule in the milk. This is when the fun begins.
"The molecules of fat bend, roll, twist, and contort in all directions as the soap molecules race around to join up with the fat molecules. During all of this fat molecule gymnastics, the food coloring molecules are bumped and shoved everywhere, providing an easy way to observe all the invisible activity. As the soap becomes evenly mixed with the milk, the action slows down and eventually stops.
"Try adding another drop of soap to see if there’s any more movement. If so, you discovered there are still more fat molecules that haven’t found a partner at the big color dance. Add another drop of soap to start the process again."
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