PROCEDURE:

1. Determination of Number of Drops per Milliliter

a. Obtain a "micropipet" as directed by your instructor.

b. Lightly rinse a graduated cylinder with the oleic acid solution. Fill the cylinder to the 3m1 mark.

c. Count the number of drops of solution dispensed from your micropipet that is needed to fill the graduated cylinder to the next milliter mark and record the-number in your notebook.

d. Repeat the counting procedure two more times and record the numbers in your notebook.

e. Calculate and record the average number of drops (from your micropipette) contained in lml of acid solution.

2. Preparation of Water Surface

a. Thoroughly clean the tray by scrubbing with soap and water, then rinsing well with water. Any traces of oil or soap on the tray will interfere with the experiment.

b. Fill the tray to a depth of about lcm with water. (Hot water has been found to give good results, but you may wish to experiment with warm or even cold water).

c. Using a shaker bottle, evenly dust the surface with just enough 1ycopodium powder so that the dust is barely visible. NOTE: If the powder is too thick the acid cannot spread out on the surface. If the powder is not evenly distributed, the film will form an irregular shape whose area cannot be calculated. The secret is to have an evenly distributed minimum amount of 1ycopodium powder so that the acid willfbrm a circular, monomolecular film.

3. Formation of the Acid Film

a. Drain a few drops of oleic acid solution from your micropipet to insure that the drop used will be of uniform size.

b. From a height of one inch above the surface, allow one drop of the acid solution to fall to the center of the pan.

c. The alcohol in the solution will either dissolve in the water or evaporate, leaving only the acid on the surface. It will push back the powder and form a clear, circular film.

d. Measure the diameter of the film across four or five directions, being careful not to jar the tray or disturb the film.

e. Record your measurements then calculate and record the average diameter of the film.

f. Discard the contents of the tray and clean it again.

g. Do a second and a third determination of the diameter of the oleic acid film formed from one drop of the oleic acid solution.

CALCULATIONS:

Do these calculations three times (once for each run) fusing-your average value of film diameter for the trun.

1. Calculate the volume of acid in the film.

Vol, m1 = ( 1drop acid solution) {(1ml acid solu.) / (Number drops acid solu.)} {(0.002 ml acid) / (1ml acid solu.)}

2. Calculate area of acid film.

A, cm² = π (d/2)²

3. Calculate height of acid film (1m1 = 1 cm³)

Height, cm = Volume, cm³/area, cm²

4. Calculate Volume of One Acid Molecule

Volume, cm³ = (Height, cm)³

5. Calculate Avogadro's Number

  A.N. = (Mol. mass / acid) (1 / density acid) (1 / Volume 1 molecule)

Therefore

A.N. = (282.5g) (1 cm³ / 0.895g) (1 molecule / Volume, 1 molecule, cm³)

QUESTIONS. (include in your write-up)

1. Using one of your sets of data, calculate Avogadro's Number assuming the molecule to be a rectangular solid with a height equal to twice its side.

2. Using one of your sets of data, calculate Avogadro's Number assuming the molecule to be a cylinder with a length equal to twice the diameter with empty space between the packed cylinders equal to 10% of the total area.

3. Yellowstone Lake has an area of 88,960 acres. How many liters of pure oleic acid (molecular mass = 282.5 and density = 0.895g ml^-1) would be needed to cover this lake with a layer one molecule thick? Assume the oleic acid molecule occupies a cubic space and 1 acre = 4047m².