Black Pepper & Dish Soap Experiments

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Whether you want to teach your child about the properties of water or are simply looking for a fun rainy-day activity, all you need are a few common household items. The U.S. Army Corps of Engineers and the Simplot Education Council recommend several experiments to observe water properties. These experiments demonstrate how water molecules are attracted to one another, pulling on each other in such a way called surface tension.

Tools

  • Assemble together a bar of soap, several pennies or marbles, black pepper flakes, a small length of string, a paper clip, a fork and a needle. You will also need a small plastic basket such as one berries are packaged in.

    Talcum powder can be used in addition to or in place of the pepper. A bottle of liquid dish detergent can be used in place of the soap bar.

    Fill three shallow dishes and a small cup with water. Glass or tin pie plates will work well for these demonstrations. To make cleanup easier, lay down several sheets of newspaper or a towel under the bowls before filling them with water.

Experiments

  • For the "runaway pepper" experiment, fill a dish with water and sprinkle the pepper or talc onto its surface. The pepper flakes should cover the surface of the water. Watch what happens when you dip a bar of soap or a drop of detergent into the dish. Dip your finger or the fork into the water to see if the surface tension breaks and makes the pepper run away.

    Use the other objects you have assembled to conduct similar experiments. Drop the pennies or marbles into a cup of water. Observe how many objects can be dropped into the water before the cup overflows. Place the length of string into the second dish, making a circle around the dish with the string. Put a drop of soap in the middle of the string. Place the needle, paper clip and berry basket in the third dish and then drop in some soap.

Observations

  • As the soap breaks down in the water, it ruptures the surface tension. This forces the pepper and the string to pull outward as they are tugged by the water molecules to remain with the unbroken surface tension, making it appear as if they are running away from the soap. The needle, paper clip and basket will sink to the bottom of the dish as the soap breaks the surface tension.

References

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