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1.To determine the length (long dimension) and width (short dimension) of oleic acid molecules.

2.To determine the number of individual molecules in a single drop of pure oleic acid.

3.To determine the mass of a single molecule.

a.lycopodium powder

b.oleic acid solution(3.6 × 10^-3 g/mL) in methanol

c.H2O

d.methanol (CH(3)OH)

e.lab notebook

f.tray

g.dropper

h.transparency sheet

i.marker

j.1 cm graph paper

k.10 mL graduated cylinder

1.Carefully fill a dropper with methanol. This solvent has a high vapor pressure and will build up pressure inside the dropper, pushing the it out. When you fill it do so by repeatedly drawing methanol in and out of it to reduce the build-up of pressure. Store the pipet in a beaker to contain drips.

2.Count the number of equal-sized drops it takes to equal a volume of just over 1 mL in a 10-mL graduated cylinder. Be sure to read the volume exactly, to the nearest 0.01 mL and do not try to make the volume you measure equal 1.00 mL exactly.

3.Calculate the volume of a single drop of methanol and write it down.

4.Fill the tray 2 cm deep with H2O.

5.Form a very thin layer of lycopodium powder on the surface of the H2O. Try to do this in a way that is repeatable.

6.Fill the same dropper with oleic acid solution. Use the same procedure as with the pure methanol.

7.Place a single drop on the lycopodium-covered water. Oleic acid dissolves in methanol and methanol dissolves in water. When you drop the solution onto the water the methanol dissolves in the water and all that is left on the surface is oleic acid.

8.Observe what happens and write down your observations.

9.Experience has shown that the spot tends to grow after a while. This may be due to piled-up oleic acid molecules spreading out. Consider: what effect will it have on your determination of the length of a molecule if you measure the area when it has piled-up molecules? What effect would it have on your determination if you measure the area after it has spread out beyond the limits of the area actually covered by the monolayer of oleic acid?

10.Use the transparency film and marker to trace the perimeter of the spot of oleic acid.

11.Lay the transparency over the graph paper and determine the area in square centimeters (cm^2).

12.Repeat the procedure atleast three times in order to be able to provide an average, range and precision. More repetitions may be necessary as determined by the quality of your data. Calculate the length of a molecule using your results from each trial while you are still in the lab. Using that information decide whether you would like to do another trial. Perhaps you might change something about your technique: if so, be sure to record this in your notebook.

Do the following calculations in your lab notebook. 

1.Use the concentration of oleic acid (3.6 × 10-3 g/mL) and the density of oleic acid (0.890 g/cm3) to determine the mass and volume of pure oleic acid in one drop of the methanol solution. You determined the size of the drop in step two above.

2.Using the volume formula relating volume, area, and height, find the height of the spot of oleic acid. Use the volume of pure oleic acid determined in the previous step. Since the oil spreads out to an area only one molecule thick, this is the length of the molecule. Report your answer in cm and nm.

3.Calculate the width of the molecule in cm and nm. Assume that the molecule is 1/4 as wide as it is tall.

4.Assuming that the base of the molecule is a square, find the area of the base of the molecule in cm2. Use that result to calculate the number of molecules in the spot of oleic acid.

5.Calculate the mass of one molecule using the mass of oleic acid in one drop (the mass of oleic acid in the spot) and the number of molecules.