When teaching about combustion, we must remember to consider ‘complete’ and ‘incomplete’ combustion.
During complete combustion, the fuel will produce CO2 and H2O.
Incomplete combustion produces CO or C (soot).
A neat way of showing this to your class is to just use a bunsen burner. With the air hole closed, explain that the smoky, yellow flame is caused by incomplete combustion – the soot can be collected by placing a cool beaker of water under the flame.
Opening the air hole allows complete combustion to take place – and the colour and properties of the flame dramatically changes.I have found that by just using the simple bunsen burner in this context allows many students to finally appreciate what happens every-time they use the bunsen burner and many a good discussion comes from this simple idea.