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We select an oil molecule because it has a density less than the density of water. Oil floats
on the surface and does not dissolve in the water. If the water has a large enough surface
area, we assumed that thin oil will spread out in a layer one molecule thick called a
monomolecular layer and not form little "hills" of molecules. If we know the original volume
of oil and the surface area that it forms, then we can calculate the thickness of a
monomolecular layer dividing the volume by the area. Use a tray with area > 30 cm2 so as not
to restrict the oil film. Sprinkle the surface of the water with a very fine light powder, e.g.
talc powder. When you put oil on the water, it pushes the powder aside so you can easily see
the area covered by the oil. Pour thin petroleum distillate oil into a burette. Find the volume
of fifty drops by running oil from the burette drop by drop and counting the drops. Allow
one more drop to fall on a piece of plastic. Touch the oil drop with the point of a glass rod
and then touch the prepared water surface. The oil spreads out. Measure the approximate
area over which it spreads. Estimate what fraction of oil was removed by the glass point by
using the glass point to remove successive fractions from the drop until it has been used up.
The volume of oil put on the water can be calculated and an estimate made of the thickness
of the oil layer, about 10-6 mm. This is an approximate dimension of a single molecule of the oil.
sharon kalunda answered the question on April 12, 2019 at 08:12
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