To demonstrate how soap can break the surface tension of milk while creating a color burst
- Milk (whole)
- Dinner plate, saucer, or pie pan (clear is best)
- Food coloring (different colors)
- Dishwashing soap (we prefer Dawn®)
- Cotton swab
Pour enough milk into the dinner plate/saucer to completely cover the bottom. Allow it to settle. Add to the milk one drop of each of your food colorings. Keep the drops close together, but not touching, near the center of the plate. Place a drop of liquid dish soap on the tip of the cotton swab. Place the soapy end of the cotton swab in the middle of the milk, and hold it there for ten to fifteen seconds.
Milk is mostly water, but also contains vitamins, minerals, proteins, and tiny droplets of fat. When you add soap, the weak chemical bonds that hold the proteins in the milk have changed. The molecules of protein and fat move away from each other in all directions. The food color molecules are shoved everywhere, too. Another reason you see the exploding colors is due to surface tension. Because milk is mostly water, it has surface tension. This means the drops of food coloring in the milk tend to stay in place until the liquid soap breaks the cohesive bonds of water molecules. The food coloring will burst into colors, moving throughout the entire surface.