4D40.10 - Monomolecular Layer

See paragraph one in the procedure section.
See paragraph two in the procedure section.
Code Number:
Demo Title:
Monomolecular Layer
Molecular Dimensions
Area of Study:
Heat & Fluids
Oleic Acid, Petri dish, Small Syringe, Pyrex pie plate, sugar cubes, table salt (approx. 9cc), 10ml graduated cylinder, transparent mm ruler, Lycopodium powder, BB's.

Put some water into the petri dish and add several drops of Oleic Acid.  Allow time for the layer to spread and then make approximate measurements to determine the diameter of the drop.  Assuming the the oleic acid layer is only one molecule thick, calculations for molecular size, weight, volume, etc. may be made.  

Fill the bottom of the pie plate with a single layer of sugar cubes. The total volume of the cubes is most easily done by measuring the space left by them in the box they came in. From this compute the height of layer. Use this to find the volume of a single cube and divide into the total volume of the layer to compute the number of cubes used. To compute the density of the cubes, divide the total given weight of the full box of sugar cubes by the internal dimensions of the box. From this the weight of a single cube can be determined. 

This simulation can also be done using BB's and a graduated cylinder to measure a volume of BB's.

This method can also be used for the salt crystals. To actually measure the crystals, make a 35mm slide of salt crystals taped to a mm scale with transparent tape. All of these methods can be used to demonstrate how the oleic acid mono-layer experiment is done. 

Lycopodium powder may be dusted onto the surface of the water so that the spot of oil can be clearly seen when using the overhead projector.

  • Carlos H. Worner, "Units and Terms", "TPT, Vol. 50, # 1, Jan. 2012, p. 6.
  • Beth Schaefer, Edward Collett, Anne Tabor-Morris, Joseph Croman, "An Estimation of the Number and Size of Atoms in a Printed Period", TPT, Vol. 49, # 7, Oct. 2011, p. 438.
  • Roger F. Larson, "Laying the Foundation for the Size of a Molecule", TPT, Vol. 27, # 6, Sept. 1989, p. 458.
  • P. Joseph Garcia and Stephen G. Wukovitz, "Before the Molecular Monolayer Experiment",TPT, Vol. 16, # 6, Sept. 1978, p. 379.
  • Elmer L. Galley, "Preludes to the Monolayer Experiment", TPT, Vol. 4, # 1, Jan. 1966, p. 34.
  • A. P. French, "Earliest Estimates of Molecular Size", AJP, Vol. 35, # 2, Feb. 1967, p. 162.
  • Robert L. Grossman, "Unusual Wind Effect on a Lake-Surface Monolayer Film", Physics Today, Jan. 2015, p. 10.
  • J. E. Greene, "Organic Thin Films: From Monolayers, on Liquids to Multilayers on Solids", Physics Today, June 2014, p. 43.
  • Jearl Walker,  "Funny Things Happen When Drops of Oil or Other Substances Are Placed on Water",  The Amateur Scientist,  December, 1983.
  • Jearl Walker, "2.148, Slight Ridge on Moving Water", The Flying Circus of Physics Ed. 2, p. 144.
  • W. Bolton, "The Size of a Molecule", Book I - Properties of Materials, Physics Experiments and Projects, 1968, p. 29.
  • Julius Sumner Miller, Q61 & A61, Millergrams I – Some Enchanting Questions for Enquiring Minds, p. 42 & 98.

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