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CABRILLO CHEM 1B - Molecules Exist

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DO MOLECULES EXIST AND HOW SMALL ARE THEY?The contents of this module were developed under grant award # P116B-001338 from the Fund for the Improve-ment of Postsecondary Education (FIPSE), United States Department of Education.However, those contents do not necessarily represent the policy of FIPSE and the Department of Education, and you should not assume endorsement by the Federal government.by Dr. Stephem ThompsonMr. Joe StaleyMs. Mary PeacockDO MOLECULES EXIST AND HOW SMALL ARE THEY?CONTENTS2Benjamin Franklin Stills The Waves3On Clapham Pond I4On Clapham Pond II5Surface Area Calculation6Oil On Water7Agnes Pockles8Measuring Surface Tension By The Capillary Method9Contact Angles10Ionic, Polar And Covalent Bonds11Intermolecular Forces12Surface Tension13Hydrophobic, Hydrophilic And Amphiphilic Molecules14Amphiphilic Oil On Water15Amphiphilic Oil On Water16Amphiphilic Oil And Water17Modern Molecular Imaging18Diffraction19X-Ray Diffraction20X-Ray Diffraction21The Scanning Tunneling Microscope22Atomic Force MicroscopyDO MOLECULES EXIST AND HOW SMALL ARE THEY?Throughout his life Benjamin Franklin was interested in the calming effect of oil on turbulent water. In 1774, he described a series of experiments in which he poured oil on a pond in England. He observed that a teaspoon of olive oil poured on the surface spread to about one half of an acre. In an article in Philosophical Transactions64, 1774, 445-460, he also reported, as seen in the excerpt given here:also reported, as seen in the excerpt given here:Franklin searched for a scientific explanation of these phenomena because he was interested in the practi-cal problem of saving the lives of sailors shipwrecked at sea in violent storms. He didn’t realize that this simple experiment could actually be used to deter-mine the size of olive oil molecules! Before deter-mining their size, let’s explore why olive oil molecules spread on water. This alone was fascinating to Franklin because on other surfaces, olive oil doesn’t spread. How can this be?spread. How can this be?In 1989, when the Exxon Valdez grounded at Prince William Sound and spilled 10.8 million gallons of oil into the sea, the clean-up process was expen-sive and difficult because of the simple fact that oil spreads on water. Several methods to clean Prince William Sound were employed, including the use of a boom, as seen in the following picture. The boom can be pulled across the surface to collect the oil but is usually employed more as a guard to protect an area.Notice the color variation in the water. Describe the contaminated water. Are Franklin’s observations similar to yours? Why or why not?When oil is spilled on water, does it float on top, sink to the bottom, or get dispersed throughout the water?What other methods have been used to clean up oil spills.What new methods can you suggest?12345Read Benjamin Franklin,s original discussion, which is included with your course resources.BENJAMIN FRANKLIN STILLS THE WAVES2DO MOLECULES EXIST AND HOW SMALL ARE THEY?“At length being in CLAPHAM where there is, on the common, a large pond, which I observed to be one day very rough with wind, I fetched out a cruet of oil, and dropt a little of it on the water.”“I saw it spread itself with surprising swiftness upon the surface; but the effect of smoothing the waves was not produced...”“...for I had applied it fi rst upon the leeward side of the pond, where the waves were largest, and the wind drove my oil back upon the shore.”WindwardLeewardWhat would you have done next after getting this result?Why do you suppose the wind pushed the oil upon the shore when the wind does not push the water upon the shore. Or does it?Benjamin Franklin was interested in the effect of pouring oil upon troubled waters. As a practical man he thought that the effect might help prevent ships from sinking and sailors from drowning. The following quotes are from the 1774 Philosophical Transactions of the Royal Society.Why not?678ON CLAPHAM POND-13DO MOLECULES EXIST AND HOW SMALL ARE THEY?“I then went to the windward side, where they began to form...”“...and there the oil, though not more than a tea spoon-ful, produced an instant calm over a space several yards square...”“...which spread amazingly, and extended itself gradu-ally till it reached the lee side, making all that quarter of the pond, perhaps half an acre, as smooth as a look-ing-glass.”What do you think Franklin would have found if he had returned to look at the pond the next day?Why, from a molecular point of view do you think that?You might suppose that the oil spread because it was blown by the wind. Do you think that there might have been another reason why the oil spread?WindwardLeewardOlive oil is attracted to the water. How does this experiment support this statement?Olive oil is attracted to itself. How does this experi-ment support this statement?What do you think would happen if the olive oil mol-ecules were smaller than water molecules?Visit a small or medium sized pond on a windy day. Observe the character of the waves both on the leeward and the windward sides. Repeat Franklin’s experiments on both sides of the pond and describe your results.91011ON CLAPHAM POND-24DO MOLECULES EXIST AND HOW SMALL ARE THEY?Surface area bout 1/2 acre.Average thickness of oil is approximately diameter of molecule.One acre = 43,560 square feet = 4,840 square yards = 4047 square meters.It is reasonable to approximate “perhaps half an acre” as 2000 square meters.Call the surface area AA = 2000 m2Call the diameter of the oil layer D.Call the volume of the oil V.From geometry, V = ADBut eighteenth century teaspoons in museums hold approximately two cubic centimeters, so we know thatV = 2 cm3Now we can put our facts together and see that2 cm3 = 2000 m2 x DYou can fi nish the calculation.Benjamin Franklin could have done this calculation but he did not. Why do you think that he did not? What implications would it have had for the develop-ment of science if he had?We are assuming that the oil, after spreading to half an acre, was one molecular layer thick. Of what signifi cance for our assumption is the fact that after spreading to half an acre the oil STOPPED spreading.A few years ago Professor Stephen Thompson of Colorado State University attempted to repeat Franklin’s experiment by dropping oilive oil onto City Park lake in Fort Collins. It did not work. Why not?Calculate the number of


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