This activity is a good opportunity for students to exercise their hypothesis-generating skills, practice making quantitative observations, and apply what they have learned about the fire triangle and the gas tests.
Revisit the fire triangle with students, explaining the need for fuel, heat, and oxygen for a fire to ignite and continue to burn. Also emphasize that the absence of any one of these factors will prevent combustion from occurring.
Carbon dioxide, which is produced when a fuel like wax is burned, has a density about 1.5 times that of air. However, warm air is less dense than cold air and is consequently forced to the top of a sealed container.