Julie Franzak

ELED 305-42

6/5/2007

Science Area: Chemistry

Concept: Surface Tension

Solutions

Battle of 2 Liquids For Supremacy

WOW #2

Materials:

Overhead projector

Glass baking dish

Water

Food coloring

Teaspoon

Rubbing alcohol

 

Procedure:

1. Place glass baking dish on the overhead projector.

2. Pour a thin layer of water into the dish (just enough to cover the bottom).

3. Color that water by adding a few drops of the food coloring.

4. Drop ½ teaspoon of rubbing alcohol into the center of the colored water.

5. Observe the two substances struggling.

Questions:

1. Which of the two substances has the stronger surface tension?

2. Why didn’t the water attach to the alcohol?

3. What was created at the end of the struggle?

Explanation:

Water molecules are more attracted to each other than they are to air and alcohol because water has a higher surface tension than do alcohol and air. When the water and alcohol molecules pull together it is through a force called surface tension. Some substances, like alcohol, have a lower surface tension in comparison to water. When the rubbing alcohol is dropped in the middle of the water it creates a struggle. Because the water molecules are more attracted to each other and have a stronger surface tension, the water retreats from the alcohol and the alcohol follows the water because it has a lower surface tension; in doing this, the alcohol leaves a clear dry spot in the center of the glass dish. Eventually the two liquids combine and create a solution; this is caused by the alcohol spreading throughout the water. The new alcohol-water solution then covers the dry spot and create an unbroken surface.

Source:

Cobb, Vicki. “Watch A Battle As Two Liquids Struggle For Supremacy”. http://www.educationworld.com/a_lesson/showbiz_science/showbiz_science023.s html. obtained on June 1, 2007.