The Volume of a Molecule of Oleic Acid
Pairs are preferred but you may work alone if you wish. Groups of three or more are not
permitted.
The Report
One report per person. Use standard headings for lab reports. Include your data, calculations and
questions. Lay out the calculations attractively (with no scratching out) showing all steps, units,
and correct significant figures.
The Problem
If you place a drop of oleic acid and methanol into water, the methanol will dissolve into the
water and disappear, while the oleic acid will spread out onto the surface. Now get this – the
oleic acid will spread out until it is ONE MOLECULE THICK! How’s that for a thin sheet. Yet
to see it, all you need is a little dust on the surface of the water before you add the drop.
In this experiment, you will use the same basic techniques that were used to calculate the
thickness of a thin aluminum sheet. By making a few assumptions about oleic acid, and by using
significant figures effectively, we will be able to calculate the approximate mass and volume of
one single molecule – amazing!
Reagents and Equipment
large tray
sharpie
oleic acid solution
graduated cylinder
centimeter graph paper
medicine dropper
coloured water
calcium hydroxide powder – don’t inhale it
Data
Copy and complete the following table.
Coloured Water
Number of drops
in 1 cm3
Trial 1
Trial 2
Trial 3
Area of oleic acid layer = __________cm2
Procedure
1. Use a medicine dropper and a graduated cylinder to determine how many drops of water
will make up 1cm3. (1 cm3 = 1 mL) Repeat this count two more times. Record the
results in the data table. Retain this medicine dropper as it is the one you will use to add
oleic acid to the water in step 2..
“The Volume of a Molecule of Oleic Acid”
Revised January 31, 2004
Continued over …
2. Pour enough coloured water in to a tray to completely cover the bottom. Sprinkle a fine
layer of calcium hydroxide powder onto the surface of the water. When everything is
calm, place one drop of oleic acid solution in the center of the tray using the same
medicine dropper used in step 1. The powder will move away leaving an area that is
clearly defined.
3. Hold an overhead transparency above the thin layer of oleic acid (without touching the
water’s surface) and trace the shape of the oleic acid layer. Transfer the oleic acid shape
from the transparency to centimeter graph paper, so the area of the layer can be found (by
counting the squares.)
4. Pour the liquids into the sink, and clean up.
Calculations
1. Calculate and state the area of the oleic acid shape on your graph paper. Note that each
square on the graph paper is 1 cm2.
2. Calculate the average number of drops from your dropper. Then use this average to
calculate the average volume of one drop of liquid.
(V of one drop = 1.00 cm3/average # of drops)
3. The drop was not pure oleic acid. In fact, it was mostly methanol. The oleic acid
comprised only one half of one percent of the drop. Calculate the volume of pure oleic
acid in the one drop you placed in the water
(V of pure oleic acid = volume of one drop x 0.00500).
4. Calculate the thickness of the one molecule thick layer of oleic acid
(V of pure oleic acid = At
Solve for t.)
5. Calculate the volume of one molecule by assuming the length and width are one tenth of
the thickness. In other words, assume the molecule has the shape of a very tall box. The
height of the box is what we are calling t, or thickness. This is what you calculated in
step 4 above. Both the length and the width, which form the base of the box are assumed
to be 1/10 of this value. (V of the molecule = lwt).
6. The density of oleic acid is 0.80 g/cm3. Calculate the mass of one molecule of oleic acid.
(Then sit back and say, isn’t that incredible! (d = m/V
Solve for m.).
Questions
1. What is the thickness of a material that spreads over an area
of 255 cm2 and has a volume of 0.0500 cm3?
2. Using the value that you obtained for the thickness in
calculation 4, what area would be covered if 10.0 cm3 of pure
oleic acid spread over a large body of water?