Experiment 12: Avogadro's Number

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Experiment 12: Avogadro's number (hand out)


The objective of this experiment is to determine the value of Avogadro's number and the mole concept via the use of the monolayer experiment. Experimental data sheet: Attached


1. Area of monolayer

A= 3.14(8.58 cm)² / 4
A= 231 cm² / 4
A = 57.8 cm²

2. Molecules of stearic acid in monolayer

57.8 cm² x 1molecule = 2.8 x 1016 molecules
2.1 x 10-15 cm²

3. Moles of stearic acid in monolayer

Average drops of stearic acid to make up the monolayer = 6 Average drops of stearic solution in 1 mL = 96

ml of stearic acid in monolayer = 6 / 96 = .0625 ml

Grams of stearic acid in monolayer = .1ml x 1.4 x 10 -4 g ml = 1.4 x 10 -5 g

1.4 x 10 -5 gram stearic acid x 1mol stearic acid = 4.9 x10-8 mol stearic acid 284 g stearic acid

Avogadro's number = 2.8 x1016 molecules = 5.7 x 10 23 molecules/moles 4.9 x 10 -8 mol




1. A. Volume of drops in exactly 1 ml of graduated cylinder. B. Diameter of water on petri plate.
C. number of drops to make monolayer.

The number of drops to make 1 ml of stearic acid in graduating cylinder was different after 3 trials, since there is already a 1% error, more trials would yield a lower percent error. Also not reading the cylinder at eye level could give false volume readings. Reading the volume at eye level will decrease errors.

When taking the measurement of the Petri plate, errors could be made by not using the correct number of significant figures or by measuring inches instead of the needed centimeters, to avoid such errors the correct number of digits and figures should be used. Also Petri plates bottoms and tops have different...
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