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Natural Science - Year II

Unit 37: Lab - Chemistry of the Candle

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Lab Assignment for Unit 37

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Unit 37 Laboratory Activity: The Chemistry of the Candle

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

Equipment and Materials:


  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.
Candle setup


Describe your setup.

Record your measurements in a nice tabular form:

Trial #  Left-over volume Starting volume Left-over/starting
AVERAGE Left-over volume→  (average of trials 1-3)  AVERAGE ratio left-over/starting volume→  (average of trials 1-3)

Determine the percentage of the atmosphere is a gas that supports combustion based on your evidence.

Compare this to the standard answer (21%). How do you explain any discrepancies? (what are your sources of error?)