Chemical History of the Candle
Lab Assignment 3: Measuring Oxygen in the Atmosphere
LAB: Resources for Combustion
Goal: Measure the amount of atmosphere consumed by a burning candle
Materials:
- A short candle with a good wick.
- A deep pan or bowl in which you can put at least a quart of water.
- A heat proof jar (such as a canning jar) or chemical beaker.
- Matches
- A wax marker like a crayon
- A liquid measure, graduated to as much accuracy as possible (a cup measure will do, a graduated cylinder is better).
Procedure
- Melt a little wax into the pan and fix your candle into it so that it won't fall over.
- DON'T light the candle yet.
- Fill the bowl with water, but make sure that at least 1 inch of candle stands above the water line.
- Upend your jar over the candle and mark the position of the water against the jar at the start of the experiment.
- Take the jar out.
- NOW light the candle.
- Quickly upend the jar and put it back into position.
- Wait until the candle flame dies completely.
- WITHOUT MOVING THE JAR, mark the new position of the water line.
- Take the jar out of the bowl
- Fill the jar to the first mark (this should be the mark after the candle burned out) with water.
- 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....)
- Now fill the jar to the second mark (this should be the original starting mark) with water
- Pour the water into your measuring cup or graduated cylinder and record the amount. This is the volume of air you started with.
- Divide the left-over amount by the original amount: this is the non-combustible part of the air.
- Repeat the experiment for a total of three measurements and average your results.
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:
- What percentage of the atmosphere is a gas that supports combustion?
- Why do we repeat the experiment?
- Why do we average our results?
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