In part 3 of Michael Faraday’s series Six Lectures on the History of a Candle, we’ll look at the combustion process more closely.
Materials:
• One candle (a tapered candle is better than a tea candle)
• Lighter or matches
• Spoon or knife
• Glass of water
• Paper towel
Caution: Fire always requires the supervision of an adult. The adult should be the one handling any flame.
Experiment:
Light the candle. Put the utensil directly into the yellow portion of the flame. Notice that there is a black substance that accumulates on the utensil. If you move the utensil around, the black will accumulate more completely. Remove the utensil from the flame and allow it to air cool. Once cooled, place the utensil into the glass of water. Did anything happen to the black substance? You can remove the black substance with a paper towel.
A spoon held in a flame accumulates a black substance on its surface
What’s happening?
In previous installments of this series of experiments with a candle, it was stated that the byproducts of combustion are water and carbon dioxide. This statement is true only under the condition that there is a sufficient amount of oxygen available for combustion. By putting the utensil directly into the flame you are not allowing for the complete combustion because you are keeping oxygen from getting to the wax particles in the wick and so the carbon in the wax does not get the opportunity to form carbon dioxide. Because the oxygen is limited, the solid carbon (or soot) deposits on the utensil. When you put the utensil into the water, the soot may have come off and floated to the surface. Pure carbon is a nonpolar substance, so it does not readily dissolve as water dissolves polar substances like sugar and salt.
Extension:
Did the utensil look silver while it was under water? The deposit of carbon happens so quickly that it does not have time to organize itself into an orderly array of atoms but is amorphous (randomly arranged atoms), not crystalline. This causes air to be trapped against the surface and therefore the light refracts completely giving the appearance of a mirror. This resource will help explain this phenomenon:
https://www.scientificamerican.com/article/turn-soot-into-silver-with-science/
References:
https://mocomi.com/is-combustion-a-chemical-reaction/
To view past “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts.
