Finding the Percentage of Oxygen in the Atmosphere Lab
Introduction: 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.
Learning Target: I will be able to determine and calculate the percentage of oxygen in the lower atmosphere.
Scientific Question: How much oxygen is in the atmosphere?
Materials:
Small Candle
Pie Pan
Water
Matches
Grease Pencil
Large Test Tube or Small Beaker
Modeling Clay or Play-Doh
100 ml Graduated Cylinder
Procedures: (Read all procedures prior to doing lab)
1. Place a small piece of modeling clay on the bottom of the candle.
2. Attach the candle with the clay to the bottom center of a pie pan. (do not light it)
3. Fill the test tube to the top with water; empty water into a graduated cylinder and record the original volume
in Table 1. (The volume of water is equal to the volume of air in the test tube)
4. Pour the water into the pie pan. (The candle should be upright in the center)
Figure A
5. Use a match and carefully light the candle.
6. Quickly invert the test tube or beaker provided over the lit candle. Make sure
the open end of the test tube/beaker is well under the surface of the water, but
not touching the bottom of the pie pan.
[See Figure A]
7. As the candle uses the oxygen in the test tube, the candle will go out and water
will be drawn into the test tube to replace the oxygen.
8. When the candle goes out, carefully mark the level of the water on the test tube with the grease pencil.
9. Remove the test tube and invert test tube making it right-side-up.
10. Fill the test tube with water to the marked grease pencil line; pour that water into a graduated cylinder to
measure the water and record the volume in Table 1. (This number represents the volume of air in test
tube after the candle went out.)
11. To find the volume of oxygen originally in the test tube, subtract the volume of air in the test tube after the
candle went out from the original total volume of air in test tube at start.
In Table 1, record the volume of oxygen in the test tube.
12. Determine the percentage of oxygen in the air by using the formula below. Record this percentage in
Table 1.
volume of oxygen in the test tube
% oxygen in air = original total volume of air in test tube at start
X 100
Name(s) ___________________________________________________
___________________________________________________
Date ____________
Block ____
Earth Science
Table 1: Percentage of Oxygen in the Air
Original Total Volume of Air in Test Tube at Start
ml
Volume of Air in Test Tube After Candle Went Out
ml
Volume of Oxygen in the Test Tube
ml
Percentage of Oxygen in the Air (use formula)
%
Questions:
1a.) Would the same result for the percentage of oxygen in air be obtained if a larger test tube was used?
________________________________________________________________________________________
1b.) What about a larger candle? _____________________________________________________________
2) Why does the 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 the experiment?
________________________________________________________________________________________
4) How much oxygen is present in 5 liters of air? _________________________________________________
5) On the back of this page, create a pie chart of the composition of the atmosphere (using a drawing compass
to make a perfect circle). You will need to look at page 366 in your text to find the other gases that make up our
atmosphere. Use colored pencils and provide a key.
For Further Investigation:
 Try the same investigation with steel wool.
To do this, 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 test tube upside down in a beaker of water. Let it remain this way for a few days. After a
few days, not any changes. Mark any changes in the height of the water in the test tube. Find the percentage of
oxygen in the air. What percentage of oxygen in the air do you get using this method?

How would the percent of oxygen change relative to elevation?