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Combustions
The combustion of butane
1) Complete combustion of butane
The gas inside of a lighter is butane therefore the ignition of a lighter provides a simple mean to study combustion of butane.
To analyze this combustion some tests are realized:
- If a lighter flame is put in a test tube, its walls are covered with condensation. We can verify that this condensation is made of water using anhydrous copper sulfate ( it should turn blue ).
Combustion continues a few moments and then the flame goes out.
- The test tube is then used to collect gases produced during the combustion. In this tube the lime water test is positive.
The combustion therefore produces water and carbon dioxide and It consumes dioxygen and butane.
Reactants are butane and oxygen
Products are carbon dioxide and water
Chemical reaction::
Butane + dioxygen → carbon dioxide + water
It is said that such combustion is complete combustion.
2) Incomplete combustion of butane
If there is not enough dioxygen to burn all the butane then combustion is incomplete:
In addition to other products it appears a black solid compound ( carbon ) and a gaseous compound colorless, odorless and very toxic ( carbon monoxide )
Chemical reaction is then :
Butane + dioxygen → carbon dioxide + water + carbon + carbon monoxide
Comment: butane as well as methane, ethane and propane are natural gases. They burn producing water and carbon dioxide, moreover these combustions may also be incomplete.
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