Finding the Percentage of
Oxygen in the Atmosphere
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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 minerals.
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.
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Finding the % of Oxygen in the Atmosphere
 What percentage of the Earth’s
atmosphere is oxygen?
Volume of air in the test tube at
start
mL
Volume of air in test tube after
candle goes out
mL
Volume of oxygen
mL
Percentage of oxygen in air
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Birthday candle
250 ml beaker
100 ml graduated cylinder
Vis-a – vi
Large test tube
Penny
Water
Goggles: you must wear these the entire
time during the lab!
1.
Fill the test tube with water. Using
the graduated cylinder, measure
this volume of water and record it
in the Data Table. The volume is
also the volume of air in the test
tube.
2. Pour the water into the beaker.
Carefully place the penny and the
candle in the center of the beaker.
The penny should keep the candle
upright.
3. 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 beaker.
4. As the candle uses the oxygen in
the test tube, the candle will go out
and water will be drawn into the
tube to replace the oxygen.
5. When the candle
goes out,
carefully mark
the level of the
water in the test
tube with the
glass marking
pen. Remove the
test tube.
6. 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 oxygen that the
candle used.
7. 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.
8. Determine the percentage of oxygen in air
by using the formula below. Record this
percentage in the Data Table.
% Oxygen in air = Volume of oxygen in test
tube divided by the total volume of air in
test tube at start. Then multiply by 100
Volume of air in the test tube at
start
mL
Volume of air in test tube after
candle goes out
mL
Volume of oxygen
mL
Percentage of oxygen in air
1. Would the same result for the
percentage of oxygen in air be
obtained if a larger test tube is
used? 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 o f air (78.1 percent).
What property of nitrogen have you
discovered as result of the
experiment?
4. How much oxygen is present in 5
liters of air?
5. Why is oxygen such an important
part of the Earth’s atmosphere?
6. Based on your observations, what is
an effective method of putting out a
fire?