PURPOSE: To demonstrate a monomolecular layer of oleic acid molecules held together by surface tension, and to experimentally determine the length of the oleic acid molecule.
DESCRIPTION: Place the clean projection tray on the overhead projector with the ruler underneath. Cover the tray with a layer of water (over 1/8") and allow the water to settle. Lightly dust the surface with lycopodium powder, and adjust the projector so the powder and ruler are both in focus. Hold the dropper just above the center of the tray and carefully release one drop of oleic acid solution onto the water surface. A circular "hole" quickly appears in the powder film, reaching its fixed maximum diameter in a few seconds. This is the monomolecular layer of oleic acid molecules held together by surface tension. Measure the diameter of the film so that the approximate thickness can be determined.
Other details are included in an instruction sheet furnished with the apparatus.
REFERENCES: (PIRA 4D40.10) See Demonstration Reference File for further information about this experiment and a sample calculation.
EQUIPMENT: Oleic acid in methanol, 1:2800 dilution, dropper, lycopodium powder, projection tray with water, projection ruler, and overhead projector.
SETUP TIME: 5 min..
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