Chemistry demonstrations involving fire, color change, and sound leave a lasting impression on students. The “dancing charcoal” demonstration is sure to be a hit!
Oxidation of Charcoal by Potassium Nitrate
Drop a small piece of charcoal into a test tube of melted potassium nitrate and watch the charcoal dance as it burns. This is a fun and simple chemistry demonstration that illustrates decomposition and oxidation (combustion) chemical reactions. It’s a nice introduction to exothermic chemical reactions, too.
Perform the Dancing Charcoal Chemistry Demonstration
Melt potassium nitrate (KNO3) in a test tube. Flaming the test tube with a gas burner works well. Decomposition of the potassium nitrate releases oxygen (O2).
2 KNO3 → 2 KNO2 + O2
Take a piece of charcoal that is small enough to fit inside the test tube. Flame it with the burner to heat it and drop it into the test tube. Rapid combustion of the charcoal will occur as the carbon in the charcoal reacts with the oxygen liberated by the potassium nitrate.
C + O2 → CO2
The piece of charcoal will bounce around inside the test tube or ‘dance’ as it is oxidized. Because a potassium salt is used as the oxidizer, the flame that is produced has a characteristic violet color.
If you like this demonstration, a similar fiery reaction occurs when you combine potassium chlorate and sugar to make “instant fire”.