Magic Soap Experiment

What You Need:

  • Wide shallow dish
  • Water
  • Red pepper flakes
  • Bar of soap
  • Paper and pencil
  • Paper clip, penny, or marble (optional)

What You Do:

  1. Help your child fill the shallow dish with water. Have her sprinkle red pepper flakes into the dish.
  2. Ask her to write an observation about how the pepper flakes appear in the water before the soap is added. They are floating on the surface of the water. She may want to draw a picture of her observation.
  3. Have her put the bar of soap in the middle of the dish of water and watch what happens. The pepper flakes all move away from the soap to the edges of the dish!
  4. She can write about or draw her observations. Ask her if she has a hypothesis (a best guess) about what happened?
  5. Explain that water has a high surface tension which makes pepper flakes float on top. When soap is added to water, soap destroys the surface tension in the area right around the soap. Soap has big molecules that are attracted to water, interfering with water molecules and their high surface tension. Pepper flakes can only float where water has high surface tension, so the flakes move away from the soap!


Rinse the dish and refill it if your child wants to experiment with other objects in the middle besides soap, such as a paperclip, penny, or marble. She will find that these do not drive away pepper flakes like soap does; they do not put out molecules interfering with water surface tension like soap does!

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