Name: Date:
Purpose: To determine what percentage of the Earth's atmosphere is oxygen.
Materials:
 Birthday candle
 100ml Graduated cylinder
 Clay
 Safety goggles
 Foil pan
 Lighter (or matches)
 Large test tube
 Water
 Glass marking pencil
Safety Procedures: Remember to ALWAYS wear your safety goggles during this lab! Use caution when lighting the candle for the experiment.
Procedure:
1.
Roll a small piece of clay into a ball.
2.
Stick the bottom end of the candle into the center of the clay.
3.
Stand the candle in the center of the foil pan, molding the clay to the bottom of the pan.
4.
Fill the test tube with water. Using the graduated cylinder to measure this volume of water (to the nearest milliliter) and record it on the DATA TABLE in the space called volume of air in the test tube.
5.
Pour the water into the foil pan.
6.
Light the candle. Rapidly invert the test tube over the lighted candle. Don’t allow the test tube to touch the candle as it is passing over it. Make sure that the open end of the test tube is underneath the water’s surface but not touching the bottom of the foil pan or clay.
7.
As the candle uses the oxygen in the test tube the candle will go out. Water will be drawn into the tube to replace the oxygen that the candle used.
8.
When the candle goes out, mark the level of the water that's in the test tube with the marking pencil. Remove the tube from the water.
9.
Fill the test tube with water to this line. Measure the volume of water and record. The volume is the volume of air in the test tube minus the oxygen that the candle used.
10.
To find the volume of oxygen in the test tube, subtract the volume of air after the candle goes out from the original volume. Record on the DATA TABLE.
11.
Determine the percentage of oxygen in the air by using the following formula: (record all data)
% of oxygen in the air = volume of oxygen in test tube x 100
volume of air in test tube at start

Data Table:
Volume of Air in the test tube at start
Volume of air in test tube after candle goes out
Volume of oxygen
Percentage of Oxygen in the air
1.
Would the same result for percentage of oxygen in the air be obtained if a larger test tube were used? Why or why not?
2.
Would the same result for percentage of oxygen in the air be obtained if a larger candle were used? Why or why not?
3.
Why does the water in the test tube rise as the candle goes out?
4.
Nitrogen is the other major component of the air (78.1%) What property of nitrogen have you discovered as a result of this experiment?
5.
How much oxygen would be present in 5 L (5000 mL) of air? Show your work!
6.
How does your experimental data compare with the actual percentage of oxygen in the atmosphere? What are some sources of error that may explain why your results weren’t exactly as predicted?
7.
Based on your observations, what is an effective method for putting out a small fire?
8.
How does the size of the candle affect the experiment?
9.
How does the size of the test tube affect the experiment?