Polarity of Water/Surface Tension - Experiment

Name Period _ Assign #

Directions: Complete the three experiments listed, observe, and record results in your science notebook.

Experiment #1

This experiment relates to polarity as it relates to water molecules.

Procedure: 1. You will need a plastic comb and a piece of wool fabric.

2. Vigorously rub the comb on the surface of the wool fabric for a minute or two.

3. Hold the charged comb over the surface of some water in a saucer. Observe.

Observation Question:

What happened? (The charged comb should have attracted a thin stream of water - positive charges attracting the negative.)

Experiment #2

This is experiment relates to polarity of food molecules. (Source: The Salt Lake Tribune.)

Procedure: 1. You will need a balloon and a few kernels of puffed rice or wheat and a piece of wool fabric.

2. Place the cereal inside the deflated balloon. Be sure the cereal kernels are dry. Blow up the balloon and tie a knot.

3. Rub the bottom of the balloon back and forth against the wool fabric, rubbing vigorously, for about 1 minute.

4. Move your finger along the bottom of the balloon. Now, move it directly underneath the rice or wheat puffs.

Observation Questions: 1. What do the rice or wheat kernels do?

2. Does your finger attract the rice or wheat kernels or make it jump away? Why?

(The positive charges in your finger were attracted to the balloon but the positive ends of the rice or wheat puffs jumped away from the positive charges in your finger.)

Experiment #3

This experiment relates to the surface tension of water.

Procedure: 1. You will need two bowls of water, some ground pepper, and dish detergent.

2. Sprinkle ground pepper on the surface of the water in one bowl and a drop of dish detergent on the surface of the water in the second bowl. 3. Observe what happens. Record results in your science notebook.

Observation and Questions: 1. What did you observe in each bowl? Was the reaction the same?

2. Write a statement explaining what happened.

NOTE TO TEACHER: For all three experiments, refer to the transparency SURFACE TENSION to help students understand the scientific phenomenon of polarity causing cohesion causing surface tension and polarity causing adhesion causing capillary attraction.