Avogadro

The thickness of the film, which is the length of one molecule, may be calculated from a knowledge of the volume of oleic acid in the drop comprising the film, and the area of the film, since volume of the film = (area)x(thickness). If the simplifying assumption is made that the molecules are boxes with a length 10 times larger than their width, then the volume of one molecule is equal to (width)(width)(length). From the known density and molar mass of oleic acid, the molar volume is calculated, using the definition of density (d=m/v). Finally, Avogadro's number can be determined by dividing the molar volume by the molecular volume to determine the number of molecules in one