Pepper in Water

DESCRIPTION:
Water has a very high surface tension because of the strong hydrogen bonding between water molecules, which allows the pepper to float on top of the water. When a small amount of soap is added it forms a monolayer on the surface. The monolayer spreads away from the point of contact causing the pepper to move to the edges of the dish.

TOPICS COVERED:
hydrogen bonding
surface tension
monolayers
physical change

MATERIALS NEEDED:
– petri dish
– pepper
– water
– soap solution

PROCEDURE:
1. Put some water in the petri dish
2. Sprinkle some pepper onto the water
3. Dip a finger, or a stir rod into the soap solution and then into the water

ADDITIONAL COMMENTS:
This would work well on an overhead.

SAFETY:
Safety goggles should be worn at all times.

Handout