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.

By Arthur Jan Fijałkowski (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

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.