# A small drop of oil has a volume of 5x10^-8 m^3. When it is put on the surface of some clean water, it forms a circular film of 0.1 m^2 in...   area. What is the size of a molecule of...

### A small drop of oil has a volume of 5x10^-8 m^3. When it is put on the surface of some clean water, it forms a circular film of 0.1 m^2 in...

area. What is the size of a molecule of oil? State any assumptions you make in your calculation.

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nessus | High School Teacher | (Level 2) Adjunct Educator

Posted on

Assumption: the circular film is one molecule thick (a monolayer).

The circular film can be treated as a cylinder with a very large cross-sectional area compared to its height which is the same as the size of one molecule. Imagine a million ping pong balls floating in a circular patch on a lake.

The volume of the film is the same as the original drop.

Volume of a cylinder, V = A x h     (A = area of film, h = height)

Rearrange for h:   h = V / A  =  (5 x 10^-8)/(0.1) = 5 x 10^-7 m

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