Course Icon
Chemical History of the Candle

Lab Assignment 3: Measuring Oxygen in the Atmosphere

Course Materials are always under revision! Weblecture content may change anytime prior to two weeks before scheduled chat session for content.

SO Icon

LAB: Combustion

Students taking Scholars Online AP Chemistry in the fall should consult with the instructor for additional AP lab instructions to use for this experiment.

Goal: Measure the amount of atmosphere consumed by a burning candle

Materials:

Procedure

  1. Melt a little wax into the pan and fix your candle into it so that it won't fall over.
  2. DON'T light the candle yet.
  3. Fill the bowl with water, but make sure that at least 1 inch of candle stands above the water line.
  4. Upend your jar over the candle and mark the position of the water against the jar at the start of the experiment.
  5. Take the jar out.
  6. NOW light the candle.
  7. Quickly upend the jar and put it back into position.
  8. Wait until the candle flame dies completely.
  9. WITHOUT MOVING THE JAR, mark the new position of the water line.
  10. Take the jar out of the bowl
  11. Fill the jar to the first mark (this should be the mark after the candle burned out) with water.
  12. Pour the water into your measuring cup or graduated cylinder and record how much water you had. This is the volume of air left after the flame exhausted the whatever-it-is in air that keeps things burning (yes, we know it is oxygen, but we're trying to be Lavoisier at the moment....)
  13. Now fill the jar to the second mark (this should be the original starting mark) with water
  14. Pour the water into your measuring cup or graduated cylinder and record the amount. This is the volume of air you started with.
  15. Divide the left-over amount by the original amount: this is the non-combustible part of the air.
  16. Repeat the experiment for a total of three measurements and average your results.
Combustion Lab Setup

Report

Describe your setup and procedures. Record your measurements in a nice tabular form:

Trial #  Left-over volume Starting volume Left-over/starting
 1      
 2      
 3      
 --  --  AVERAGE →  

Be sure to address the following questions in your conclusions:

  1. What percentage of the atmosphere is a gas that supports combustion?
  2. Why do we repeat the experiment?
  3. Why do we average our results?