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        Observation

• The candle went off after sometime.
• The level of sodium hydroxide rose in the gas jar but dropped in the water trough.

        Discussion

• The candle burns for a while then it goes off. As the candle burns, it uses up the active part of air in the fixed amount of air enclosed in the gas jar. This leaves a vacuum in the jar. Greater atmospheric pressure acting on the surface of the sodium hydroxide forces the solution up to in the jar.

• Sodium hydroxide therefore rose in the gas jar to occupy the volume which were previously occupied by the part of air used up during combustion.

                 The following are the sample results for a similar experiment

• Height of air column before burning  = 16.0cm

  Height of air column after burning     = 12.9cm

  Height of air used during burning       = 3.1cm

  To calculate the % of air by volume used up

                                        = Height of air used    X  100%

                                           Initial height of air

                                             = 3.1  X 100%

                                                16.0

                                             = 19.375 %

• Combustion/ burning is a process in which a substance combines with oxygen with the production of heat.
• The part of air that supports combustion is the active air.
• The active part of air is Oxygen which forms about 20% of dry air by volume.
• The part of air that remains in the gas jar does not support combustion.The main component of this inactive air is Nitrogen.