This was one of my favorite experiments as a kid. When you mix some milk, food coloring, and liquid dish soap, an interesting reaction takes place. With this kitchen chemistry project, you’ll amaze friends and family and learn the science behind soap!
- Milk (2% or whole). (Amazon link: Whole Milk)
- Food coloring (multiple colors). (Amazon link: Food Coloring)
- Liquid dish soap (Amazon link: Dawn Dish Soap)
- Cotton swabs (Amazon link: Cotton Swabs)
- Dinner plate or shallow bowl
- Pour some milk into the dinner plate or shallow bowl. Make sure there is a depth of about 1/4 inch.
- Add a drop or two of each food color to the plate. Keep them close together in the center of the plate.
- Place a small drop of dish soap on one end of a cotton swab. Touch this end to the center of the plate, but don’t stir. Hold it there for about 10 seconds. Watch what happens.
- Add another drop of dish soap to the tip of your cotton swab. Now, try placing it in different areas of the plate. What happens?
- Instead of milk, repeat the experiment with water. Does this produce the same result?
- Try using different kinds of milk: skim, 1%, 2%, and whole. Which produces the best results?
Milk contains water, proteins, minerals, vitamins, and suspended fat. Because proteins and fats are suspended in solution, they react to changes in the milk. Liquid dish soap weakens the chemical bonds that help suspend these fats and proteins. This happens because of dish soap’s molecular structure. One end of the structure is non-polar and the other is polar. The non-polar end is hydrophilic, or “water-loving.” This end dissolves in water, the main substance in milk. The dish soap’s hydrophobic (“water-fearing”) end clings to the suspended fat molecules. However, the fat tries to “run away” from the soap in different directions. Meanwhile, the food coloring molecules get shoved around in all the havoc. Hover, the soap begins to mix and dissolve evenly with the milk, which eventually stops the action. Therefore, higher fat content (e.g. 2% or whole) creates a better spread of color. More fat needs to combine with the soap molecules in order to stop the action.