University of Pittsburgh at Bradford
Science In Motion
Chemistry Lab 026
ANALYSIS OF MOUTHWASH
Introduction:
Commercial mouthwashes are mixtures of water, alcohol, dyes, flavorings, and other compounds.
This experiment will allow the alcohol content of the mouthwash to be determined. If fifty milliliters each
of alcohol and water are mixed, the total volume of the mixture will not equal one hundred milliliters.
This reduction in volume is due to the attractive forces between the alcohol and water. Since the volumes
of alcohol and water are not additive when mixed, a calibration curve must first be prepared. It will
provide the correction needed for alcohol-water mixtures. The calibration curve will be prepared by
placing a known amount of alcohol in an alcohol-water mixture. The observed percentage of alcohol will
be plotted against the true percentage of alcohol.
Once the calibration data is collected and plotted, samples of mouthwashes will be analyzed using
the gas chromatograph. The observed percentage of alcohol will be determined, and the true percentage
will be found using the calibration graph. These values may then be compared with the values reported by
the manufacturer.
Purpose:
The purpose of this experiment is to determine the amount of alcohol in a brand of mouthwash.
Equipment/Materials:
ethanol
100 mL volumetric flasks
gas chromatograph
mouthwash samples
distilled water
pipet or buret
10 L syringe
Safety:



An apron and goggles should be worn in the laboratory at all times.
The chemicals used in this experiment should pose no significant safety hazards.
Good laboratory procedure should be followed at all times.
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Procedure:
1. Turn on the GC.
2. Start the Peak Sample software.
3. Set the following conditions from the edit menu by selecting channels, then selecting channel 1
and temperature change.
Start 140C
Hold 5 minutes
Ramp 0 degrees / min
Until the temperature is 140C
4. Be sure the time scale starts at zero. Use the arrow to adjust.
5. Prepare standard solutions of ethanol according to the following list if 95% ethanol is used. Each
lab group should prepare solutions as assigned by the instructor.
Solution
A
B
C
D
% volume alcohol
5%
10%
20%
30%
95 % alcohol (mL/100 mL)
5.26
10.53
21.05
31.58
6. Obtain a microliter syringe and a sample vial containing one of the samples to be tested.
7. Rinse the syringe 6 times with the sample to be tested. Then obtain 1 microliter of the sample in
the syringe.
8. Click on the Z or  button on the run screen to zero the current.
9. Insert the needle on the syringe into the injection port. At exactly the same time that one member
of the group injects a sample, a second group member will press the space bar on the computer to
begin the data collection.
10. After this peak is recorded, press the end button on the compouter.
11. Repeat steps 2 through 5 for all standards and as many unknowns as time permits.
12. Determine the area under the peak by carefully cutting out each peak and massing or by using the
equation A=1/2 bh.
13. Plot % area alcohol (y-axis) vs. % alcohol (x-axis). Draw a best fit line. Use this calibration
graph to determine the % alcohol in the original mouthwash sample.
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ANALYSIS OF MOUTHWASH
STUDENT EVALUATION
Data Table:
Percent Alcohol (v/v)
30
20
10
5
Brand
Area Due to Alcohol
Area Due to Alcohol
% Alcohol
Accepted Value
3