Color Changing Milk Experiment

Materials

• Milk (whole or 2%)

• Dinner plate

• Food coloring (we like this set)

• Dishwashing soap

• Q-Tips or cotton swaps

Directions

1. Pour enough milk onto the plate to completely cover the bottom to the depth of about 1/4.” Allow the milk to settle.

2. Add 1 drop of each of the four colors of food coloring — red, yellow, blue, and green — to the milk. Keep the drops close together in the center of the plate.

3. Touch the tip of the Q-Tip to the center of the milk. It's important not to stir the mix. Just touch it with the tip of the cotton swab. Did anything happen?

4. Now dip the Q-Tip in dish soap. Place the soapy end of back in the middle of the milk and hold it there for 10-15 seconds. Look at that burst of color.

5. Add another drop of soap to the tip of the Q-Tip and try it again. Experiment with placing the cotton swab at different places in the milk. Notice that the colors in the milk continue to move even when the cotton swab is removed.

Why 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.

adapted from Steve Spangler Science.