How to find out Oxygen ratio in air by Candle combustion

Water goes up the level 1/5.

How to find out Oxygen ratio in air by Candle combustion

Materials 
candle, glass vessel or PET bottle, match, plate, sodium hydroxide, and water

Procedure 

1. The sodium hydroxide is dissolved in water and the solution of 3% is made.
2. The candle is fixed in the plate.
3. Light the candle.
4. Cover it with the glass vessel or the PET bottle.
5. Confirm the water level and the ratio of the volume.

Science 
When burning, the candle uses the oxygen in the air. The water made by burning reduce the volume about 1/1700 after cooling and becoming the liquid. As for remaining carbon dioxide, it reacts with the sodium hydroxide and the sodium carbonate is made. It is absorbed to the solution. Therefore, water which is almost same volume of the oxygen rises in the container.

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