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Grade Levels 6-12
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| Experiment:
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HOW TO MEASURE THE WALL THICKNESS OF A SOAP BUBBLE
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| Equipment:
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- Ohaus 0.01g resolution balance (Scout SC2020 or Navigator NV-410)
- Small 10 gallon aquarium
- Vinegar - 1 pint
- Baking soda - ½ cup
- Bubble solution*
- Ring or straw to blow bubble
- Millimeter ruler
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| Procedure:
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- Place vinegar in aquarium.
- Add baking soda and cover with a piece of cardboard or paper to keep room
air currents from disturbing the gas (CO2).
- Find mass of a highly absorbent paper towel. Record mass by 0.01g.
- Carefully remove cardboard cover and blow a bubble (approx. 6-7 cm in diameter).
- While it rests on the "bed" of CO2, measure the diameter, then slide the paper
towel piece under the bubble, letting it collapse on the towel.
- Find the mass of the bubble, plus the towel.
- From the diameter of the bubble, calculate the area of the bubble. Divide the mass of
the bubble by the area.
- Assuming the mass of the bubble in grams to be equal, numerically,
to its volume in cubic centimeters, its wall thickness will be in the order
of 3-5 microns. This will probably be the thinnest film the students will ever have measured.
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*Bubble solution: To make bubble solution, mix 100 ml of DawnŽ or Joy® dishwashing
liquid with 50 ml of glycerin. Add this to 850 ml of distilled water. Stir, do not shake.
For longer lasting bubbles, increase the amount of detergent to 200 ml.
(By David Katz community College of Philadelphia.) Distilled or
deionized water improves results. Apparently, metal ions in the water are troublesome.
Contributed by: Verne N. Rockcastle Professor Emeritus Science & Environmental Education
Cornell University
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