Milk Fireworks
[Shopping list: whole milk; half & half milk; skim milk; shallow plastic bowls; food colors; Q-tips or toothpicks; liquid dish detergent]
- Carefully place one drop each of 4 different food colors on the surface of a dish of whole milk. Keep the colors evenly spaced on the surface of the milk, not in the middle, but not at the very edges either.
- Dip just the very end of a Q-tip or toothpick into a small dish of liquid dish soap, then touch the Q-tip to the surface of the milk in the center of the bowl. The colors should immediately disperse in random designs that resemble fireworks.
What's Happening: Milk is an even (homogenous) of fats, sugars, proteins, and mostly water molecules. This is called an emulsion, or a mixture of liquids that cannot be truly blended. Because fatty acids and proteins have both hydrophilic (water-loving) and hydrophobic (water-hating) regions, they arrange themselves in the most energetically favorable manner in order to stay suspended in the water. Thus, the surface of the milk is in a complex state of equilibrium. The molecules of dish detergent, like fats and protein, have both hydrophilic and hydrophobic regions, so adding them to the surface of the milk disrupts the existing state of equilibrium. On a molecular level, the surface of the milk is in a state of chaotic disarray and takes the food color with it as it tries to return to equilibrium. Explain to the kids that the molecules on the milk surface are “where they want to be” and don’t like to be disturbed. Then come along those annoying soap molecules that like to stir things up (on a microscopic level, of course). Because milk is all white, we wouldn’t normally be able to see things happening. The food coloring lets us do this.
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