Finding the Percentage of Oxygen in the Atmosphere
Intro (Review Activity ) – Make a pie chart of the data table below, illustrating the elements present in
the Earth’s crust. Include color (or design patterns), a key, and a chart title. Show your calculations for
the first three elements.
Element
Element Percentage
# of
Symbol in the Crust
Degrees
Oxygen
46.6
Silicon
27.72
Aluminum
8.13
Iron
5
Calcium
3.63
Sodium
2.83
Potassium
2.59
Magnesium
2.09
Titanium
0.4
Hydrogen
0.14
Total
99.13
Finding the % of Oxygen in the Atmosphere
Background Information
The atmosphere of the earth is composed of a mixture of gases. The two most
abundant gases are nitrogen and oxygen. Oxygen also appears in the earth’s crust combined
with other elements to form materials.
In this investigation, you will study how much of the air is consumed during combustion.
By measuring volume, you will be able to determine the percentage of oxygen in the air.
Problem – What percentage of the earth’s atmosphere is oxygen?
Materials (per group)
 Birthday candle
 250 mL beaker
 100 mL graduated
cylinder




Matches
Glass-marking pencil
Large test tube
Penny


Water
Safety goggles
Procedures
1. The penny should have some clay on it and should be holding the candle upright.
2. Fill the test tube with water. Using the graduated cylinder, measure this volume of
water and record it in the data table. The volume of water that the tube can hold is the
same as the volume of air that it can hold.
3. Pour the water into the beaker. Carefully place the penny with candle into the center
of the beaker. The penny should keep the candle upright, and the water level needs to
be lower than the middle of the candle.
4. Carefully light the candle, and rapidly flip 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 beaker. See Figure 1.
5. As the candle uses the oxygen in the test tube, the candle will go out as the combustion
occurs. The water will be drawn upwards into the tube due to the pressure.
6. When the candle goes out, carefully mark the level of the water in the tube with the
glass-marking pencil. Remove the test tube.
7. Fill the test tube with water to this line. Using the graduated cylinder, measure this
volume of water and record it in the data table. The volume is the volume of air in the
test tube, minus the amount of oxygen that the candle used.
8. 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. Record the volume in the data table.
9. Determine the percentage of oxygen in air by using the formula below. Record this
percentage in the data table.
% oxygen in the air = volume of oxygen in test tube
x 100
total initial volume of air
Figure #1
Observations
Volume of Air in the Test Tube
Volume of Air in the test tube after candle goes
out
Volume of Oxygen
Percentage of Oxygen in the air
mL
mL
mL
Conclusions
1. Would the same result for the percentage of oxygen be in air be obtained if a larger test
tube was used? A larger candle?
2. Why doe water rise in the test tube as the candle goes out?
3. Nitrogen is the other major component of air (78.1%) What property of nitrogen have
you discovered as a result of this experiment?
4. How much oxygen is present in 5 L of air?
Critical Thinking
1. Why is oxygen such an important part of the earth’s atmosphere?
2. Based on your observations, what is an effective method of putting out a small fire?
Why?
3. “As altitude of an area increases, the density of the atmosphere decreases.” How can
this statement be used to explain why it is more difficult to breathe in Denver, which
has an altitude of more than 15000 meters, than in Houston, which is at sea level?
Going Further:
Try the investigation with steel wool. Place a small amount of fine, moist steel wool in
the closed end of the tube. Using a test tube clamp on a ring stand, suspend the testu tube
upside down in a beaker of water. Let it remain this way for a few days. After a few days, note
any changes. Mark any changes in the height of water in the test tube. Find the percentages of
oxygen in the air. What percent of oxygen in the air do you use getting this method?
Data Tables
Large Test Tube
Trial #1
Initial Volume of Air in the Test Tube
Trial #2
mL
mL
Out
mL
mL
Volume of Oxygen
mL
mL
Final Volume in Test Tube after candle goes
Percentage of Oxygen in Air
Medium Test Tube
Trial #1
Initial Volume of Air in the Test Tube
Trial #2
mL
mL
Out
mL
mL
Volume of Oxygen
mL
mL
Final Volume in Test Tube after candle goes
Percentage of Oxygen in Air
Small Test Tube
Initial Volume of Air in the Test Tube
Trial #1
Trial #2
mL
mL
Out
mL
mL
Volume of Oxygen
mL
mL
Final Volume in Test Tube after candle goes
Percentage of Oxygen in Air
Conclusion: Based on six trials, the percentage of oxygen in a sample of air is _______%.
Pie Chart Construction
Directions - Based on your average, complete the table below and then construct a pie chart of
the percentage of gases in the atmosphere. Include color (or patterns), a key, and a chart title.
Gases in the
Atmosphere
Percentage
Degrees
Nitrogen
Oxygen
Argon, CO2, water
vapor, and other trace
elements.
Application: Write 2 Sentences comparing what you see in the two pie charts you have
constructed for this lab.
1
2