Atmospheric Oxygen Evaluation
Determining The Percent of O 2 In Air
Integrated Science 2
Redwood High School
Name:
11/16
Period:
 Background
The Earth's lower atmosphere is a mixture of many gases called air. The two most abundant of theses gases
are nitrogen and oxygen, which make up almost 99% of dry air by volume. The remaining 1% is composed
mostly of argon and carbon dioxide, with trace amounts of an additional 10-15 different gases. These trace
amounts include a number of man-made pollutants.
The amount of oxygen in the air is of critical importance to all living organisms, including humans. It is
possible to experimentally calculate the percentage of oxygen in a given air sample using techniques and
equipment which are readily available in our lab. Because oxygen is consumed during combustion (an open
flame), the volume of air in a closed sample will decrease as a flame consumes the oxygen in that sample. We will
use this principle in our determination of the oxygen content of air.
 Focus Questions
• What is the composition of the Earth's air and how can this be represented in graphical form?
• What are the sources of the various man-made pollutants which are present in our atmosphere?
• What is the experimentally determined percentage of oxygen in the air at Redwood High School?
 Materials
Penny, Candle, Matches, Water, Glass Bowl, Test Tube, Graduated Cylinder, Glass Marking Pen
 Procedure
Part A: Experimental Determination of Oxygen Percentage
1. You will find all the necessary materials at the lab stations.
2. Light a match, melt the bottom of the candle, and then stick the candle onto the “tails” side of the penny. The
candle should stick firmly to the penny.
3. You need to determine the volume of the large test tube. To do this, fill the test tube with water. Using the
graduated cylinder, measure this volume of water and record this measured value as “Volume of Air in the
Test Tube At Start” for each Trial in Data Table 1.
4. Pour the water into the glass bowl. Carefully place the penny and the candle in the center of the glass bowl.
The penny should keep the candle upright.
5. Carefully light the candle, and rapidly invert the test tube over the lighted candle. Make sure that the open
end of the test tube is well under the surface of the water but not touching the bottom of the glass bowl.
6. As the candle burns so does the oxygen in the test tube. Once all the oxygen is used up, the candle will go out
and a volume of water equal to the volume of oxygen burned will be drawn into the test tube.
7. When the candle goes out, carefully mark the level of the water in the test tube with a glass-marking pencil.
Remove the test tube.
8. Fill the test tube with water to this line. Using the graduated cylinder, measure this volume of water. This
number equals the volume of air in the test tube after the candle used the available oxygen. Record this
value in Data Table 1.
9. To find the volume of oxygen originally in the test tube, subtract the volume of air after the candle goes out
from the original volume. The difference is the oxygen that was burned. Record the volume in Data Table 1.
10. Determine the percentage of oxygen in the air by using the formula below. Record this percentage in the Data
Table.
Percent (%) Oxygen (O2 ) in Air =
volume of oxygen in test tube
x 100
total volume of air in test tube at start
11. To improve the reliability of your data, conduct two additional trials. Record these values in Data Table 1.
12. Average the results of your percent oxygen calculations.
Data Table 1.
Trial 1
Trial 2
Trial 3
Volume of Air in the Test Tube at Start (ml)
Volume of Air in Test Tube After Candle (ml)
Volume of Oxygen (ml)
Percentage of Oxygen in Air
(round to the nearest 10 th of one percent)
% Oxygen Average
(of your three trials)
 Part B: Composition of the Atmosphere
1. Use the data in Data Table 2 to construct a graph of the composition of the gas found in the Earth's
atmosphere. Print your graph.
2. Use your graph to answer the appropriate analysis and conclusion questions.
Data Table 2: Composition of the Atmosphere
Atmospheric Gas
Nitrogen (N2 )
Oxygen (O2 )
Argon (Ar)
Carbon Dioxide (CO2 )
All remaining trace gases
Carbon Monoxide (CO), Helium (He),Water Vapor (H2 O), Ozone (O3 ), Nitrous Oxide (NO),
Xenon (Xe), Methane (CH4 ), Chlorofluorocarbons (CFC's),Sulfur Dioxide (SO2 ), Hydrocarbons,
Particulate Matter (dust, etc.)
2
% Composition
78.00 %
21.00 %
0. 80 %
0. 03 %
0. 17 %
O 2 Lab
 Analysis and Discussion Questions
 answers must be word-processed using complete sentences
1. Would the same result for the percentage of oxygen in air be obtained if a larger test tube were used? How
about a larger candle? Explain your answers.
2. Why does the water rise in the test tube as the candle goes out?
* look this experiment up online, in order to answer this question correctly
3. Nitrogen is the other major component of air (apx. 78.00%). What property of nitrogen have you discovered
as a result of this experiment?
4. Analyze and discuss the class data. What is the range of calculated values? What is the average? How does
the class average compare with the "correct" value for oxygen percentage in the atmosphere? Identify at least
two (2) potential sources of error in your results and the class results.
 Class Data
Lab Groups
% Oxygen Average
1
2
3
4
5
6
7
8
9
10
11
Class Average (% Oxygen) =
3
O 2 Lab