Molecular Forces At Work: Creating Soap Bubbles
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Laz, Jerome Everett School
To make chemistry interesting to students by showing them it is part
of the real world, rather than being confined to reagent bottles and
test tubes in the classroom laboratory.
The student will be able to:
1. discover how the terms "surface tension," "cohesion," and
"adhesion" are related to soap bubbles,
2. hypothesize the outcome of the experiments,
3. analyze experimental data and conditions,
4. relate the polarity of the water molecule to the behavior of soaps
This project is based upon molecular force and the degree of surface
tension, which depends on the amount of energy in the intermolecular
forces. Liquids that produce strong intermolecular forces have a
strong surface tension. Water molecules form hydrogen bonds between
each other and have strong intermolecular force; as a result, a strong
surface tension is created.
Soap bubbles are made up of soap molecules and water molecules. A soap
bubble has a polar end and a nonpolar end. Water is a polar molecule.
The polar end of the soap molecules are attracted to each other. The
nonpolar ends of the soap molecules stick out from the water and help
hold bubbles together.
overhead projector silk thread glycerin
Petri dishes detergent distilled water
razor blades cheesecloth
alcohol 2 small glass plates
pepper soap bubble solution
aluminum foil pipe cleaners or bubble wands
beakers pans for bubble solution
1. Float a razor blade or needle on water in a Petri dish on the
overhead projector. Surface tension supports the object.
2. Make a loop of 5" of silk thread. Float in a low, wide container
of water. Touch a bit of wet soap to the water inside of the silk
loop and notice that it becomes a circle.
3. Sprinkle black pepper over the surface of water in a Petri dish.
Add a drop of detergent to the center and watch the pepper spread
4. A hollow "boat" made of a 2" by 1" piece of aluminum foil, partly
filled with a few drops of alcohol and with a 1/2 " length of
lightweight cotton wick (such as is used in a cigarette lighter)
over the stern, will skim over water.
5. Fill a wide mouthed jar with water, cover mouth with cheesecloth,
and fasten securely. Now invert the jar quickly. If you punch a
small hole in the cheesecloth with a pointed pencil, water runs out
for an instant, but surface tension with the aid of atmospheric
pressure "seals" the hole.
6. Support a piece of window screen over a pan. Slowly pour water
onto the screen. Plain water will bead up. Detergent water will
fall through the openings.
7. Recipe for making soap bubbles:
85% distilled water
10% detergent (Joy recommended)
Students make bubbles and observe irridesent color, relative thickness
of the top and bottom of the bubble, movement of water within the
bubble, and longevity of bubbles.