Updated September 2011 Oil Drop Experiment

Updated September 2011 How can we find the height of a molecule without fancy equipment?

Updated September 2011 Ben Franklin’s Oil Drop Experiment Portrait of Benjamin Franklin by Joseph Siffred Duplessis Circa 1785 “I fetched out a cruet of oil and dropped a little of it on the water. I saw it spread itself with surprising swiftness upon the surface… Though not more than a teaspoonful, produced an instant calm over a space several yards square which spread amazingly and extended itself gradually till it reached the lee side, making all that quarter of the pond, perhaps half an acre, as smooth as a looking glass.” Ben noticed that oil would spread out very thin…

Updated September 2011 Let’s use these BBs to understand how we could find the height of a molecule. Imagine that each BB is one molecule. How can we find out how tall each one is, assuming we could not actually measure it? Image by HighPoint Learning

Updated September 2011 We know the volume of the BBs. Now, let’s pour them into a single layer. Image by HighPoint Learning

Updated September 2011 Measure the diameter of the single layer. If the shape were not a circle, how could you get a diameter? Given the diameter, calculate the Area. Area=π(Diameter/2) 2 Image by HighPoint Learning

Updated September 2011 Now, let’s determine the height of this (1 layer thick) Cylinder. Use Height = Volume/Area.

Updated September 2011 Measure the height of a single BB to see How close our calculation is. ?

Updated September 2011 Now, you will use this same method to calculate the height of a single oil molecule. Image by Ben Mills

Updated September )Prepare the oil and alcohol. Mix 9 ml of alcohol with 1 ml of mineral oil. Stir until they have combined well. Each ml of this mixture will now be 1/10 ml oil.

Updated September )Determine what fraction of a ml one drop is. Fill the pipette to a ml mark and count how many drops it takes for the level to go down to the next ml mark. How many drops are in a ml (e.g. 10 drops)? What fraction of a ml is one drop(e.g. 1/10 ml)?

Updated September )Calculate the volume of oil in the drop. The volume of oil will be the 1/10 oil times the fraction of a ml that the oil drop (e.g. 1/10 x 1/10 = 1/100 ml of oil). What is the volume of oil in one drop of the oil alcohol mix?

Updated September )Prepare the pan of water. Fill the pan with water. Beat two chalkboard erasers together over the pan leaving a very thin film of dust on the surface.

Updated September )Drop the oil drop. Place the pipette of the oil alcohol mix close to the surface of the water in the middle of the pan. Press one drop out onto the surface. It should push the chalk making a circle of oil that is easy to see.

Updated September )Measure the diameter of the oil film. Take several measurements of the diameter of the oil film and average them. What is the average diameter of the oil film?

Updated September )Calculate the area of the oil film Area = π x (Diamerer/2)2 What is the area of the oil film?

Updated September )Calculate the height of the oil film Height of the oil molecule = Volume of oil in the drop(from #3) / Area(from #7) What is the height of the oil molecule? What is the height of the oil molecule in nm?

Updated September 2011 This module is one of a series designed to introduce faculty and high school students to the basic concepts of nanotechnology. Each module includes a PowerPoint presentation, discussion questions, and hands-on activities, when applicable. The series was funded in part by: The National Science Foundation Grant DUE and the Oklahoma Nanotechnology Education Initiative Any opinions, findings and conclusions or recommendations expressed in the material are those of the author and do not necessarily reflect the views of the National Science Foundation or the Oklahoma Nanotechnology Education Initiative.

Updated September 2011 Image Credits Aumier, Guillaume (Designer) Carbon Nanotubes.svg [Digital Image]. France. Wikimedia Commons (commons.wikimedia.org) Brandrodungswanderfuldhackbau (Photographer) 787-flight-check.jpg.[Digital Image]. Germany. Wikimedia Commons (commons. Wikimedia.org) Duplessis, Joseph Siffred (Artist). Portrait of Benjamin Franklin. [Oil on Canvas]. United States. National Portrait Gallery, Smithsonian Institution Highpoint Learning Solutions. (Photographers/designers) [digital images] United States. Fokkix (Photographer). Elephants.jpg. [digital Image]. United States. Wikimedia Commons (commons.wikimedia.org)

Updated September 2011 Image Credits MilborneOne (Artists B a.jpg [Digital Image]. United Kingdom. Wikimedia Commons (commons.wikimedia.org) Mills, Ben. (Designer). Ball-and-stick model of the Oil Red O molecule. [Digital Image]. Wikimedia Commons. (commons.wikimedia.org)Oil Red O Molhave, Kristian (Professor. Fe-cat CVD MWCNT SEM overview mats with scalebar.jpg. [Scanning Electron Microscope Image]. United Kingdom. WIkimedi Commons (commons.wikimedia.org)

Updated September 2011 References Estimating the size of a molecule using an oil film (2004). Practical Physics. Retrieved from Franklin, Benjamin. The Autobiography of Benjamin Franklin. [Kindle Edition]. Retrieved from