Experiment 3: Avogadro’s Number
One mole = 6.02 x 1023 particles.
“One more of anything = 6.02 x 1023 units of that thing.”
Amadeo Avogadro
(1776 – 1856)
?
quadrillions trillions
billions
millions
thousands
1 mole = 602213673600000000000000
or 6.022 x 1023
There is Avogadro's number of particles in a mole of any substance.
Experimental Objective: Verify Avogadro’s number using a
monolayer oleic acid molecules.
• Oleic acid is a mono-unsaturated omega-9 fatty acid that occurs
naturally in various animal and vegetable fats and oils.
• Triglyceride esters of oleic acid comprise the majority of olive oil.
• It is used as a stabilizer agent in pharmaceuticals and as an
emulsifying or solubilizing agent in aerosol products.
Oleic Acid
oleic acid
Lipid monolayer at water interface
Polar head group
Form a monolayer of oleic acid:
1. Determine the amount of mole of oleic acid.
2. Determine the number molecules in the layer using the V of
the layer and V of a single molecule. We will assume
Vmolecule = Vcube
3. Calculate Avogadro’s number.
ᇱ
1
2
3
4
1. Spread some cork powder onto the water surface.
2. Drop a droplet of oleic acid and pentane solution onto it.
3. Pentane will quickly evaporate and the oleic acid will spread on the water
surface, creating a thin circular layer that is only one molecule thick (so called
monolayer).
4. Measure the diameter of the monolayer and calculate the area of the oleic acid
solution.
Procedural Flowchart
Grease rim of watch
glass
Trace shape of oleic acid
pattern on graphing paper
Cut out film shape of oleic acid.
Weigh on ANALYTICAL balance.
Add some tap water + 1
drop of HCl (aq)
Add 0.10 mL mL of oleic acid
+pentane solution. Allow
pentane to dry.
Use pipette to add water
until bulges out
Spread a thin even
layer of cork dust
(Note: You’ll need to redo
this step if the layer ends
up being too think.)
Cut out four 5.00 cm x 5.00 cm pieces from
the corners of the graphing paper. Weigh
all pieces on ANALYTICAL balance.
Data Table
Volume of Oleic acid + Pentane solution
Mass of film shape of Oleic acid
Area of film shape of Oleic acid
Mass of comparison squares (avg of 4)
Area of comparison squares (avg of 4)
0.10 mL
Calculation
Calculation
0
