Properties of Water Lab #2 - Surface Tension

Surface tension is another fun concept to explore with your kiddos! Because water molecules have a greater attraction to one another than they do to the air molecules above/surrounding them, a 'barrier' of sorts is formed on the surface of the water which can actually allow things that are more dense than water to float!

Materials

plastic cup

water

pepper

cotton ball

dish soap

Completing the Lab

  1. Provide students with a cup of water, sprinkling pepper into the cup and inviting your kiddos to observe what happens - i.e. the pepper floats due to the surface tension of the water.
  2. Given a cotton ball with a small amount of dish soap on it, invite your students to lightly tap the surface of the water with the soapy part of the cotton ball and observe the results - i.e. the surface tension is broken and the pepper scatters/sinks to the bottom of the cup.

Explanation

The molecules that make up dish soap are different than water molecules. Unlike water molecules that like to stick together, soap molecules do not stick together and do not like to stick to water molecules. In fact, soap molecules have conflicting reactions to water molecules - one part is attracted to the water, while the other part wants to push it away. Because of this, the soap molecules are able to break the bonds formed by the water molecules - i.e. break the surface tension - causing the pepper to scatter/sink.

Our photos of this lab did not turn out. The photo above was taken by Jennifer over at Training Them Up. Jennifer and her kiddos are always up to something fun, so be sure to head over there and check out the original post!


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