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"Running Pepper" Milk/Water with Pepper Experiment

By Julia Galperin

Milk/Pepper and Soap Experiment

Materials: Milk or water, pepper, soap, pan

  1. Fill bowl with a little bit of milk

  2. Sprinkle pepper flakes evenly across the surface and these flakes should float along the surface of the milk

  3. Touch finger to surface and notice how nothing happens

  4. Then put soap on your finger and notice how all the pepper flakes run away

Explanation: Pepper is hydrophobic, meaning that the water is not attracted to it. Because of this, the pepper cannot dissolve in the water. The pepper flakes float upon the top of the water because the flakes are so light and hydrophobic so the surface tension of the water keeps them floating along the surface. The pepper flakes all move because the soap is able to break the surface tension of the water and as the soap moves into the water, the surface tension changes, so the pepper is no longer floating on the top. The water molecules still want to keep the surface tension so they pull away from the soap and carry the pepper with them. 

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