Floating Candles - Experiment 6

Students will observe a combustion reaction and deduce the components necessary for the reaction to occur. They will also see the relationship between pressure, volume, and number of molecules for gasses.

Materials Substitutions
votive candle
2 400-mL beakers 2 small jars with diameter larger than votive candle
candle taper
1 large petri dish 1 aluminum pie pan
water (with optional food coloring)
matches
beaker with water jar with water

Procedure

  1. Place a votive candle in the center of a petri dish or an aluminum pie pan and light it.
  2. Carefully, pour some water into the dish or pan until the candle is floating.
  3. Quickly, place the inverted jar over the candle and allow it to rest on the bottom of the pan. Report the results.
  4. Light the votive candle again and repeat steps 1-3. Make sure you dry the inverted jar each time you repeat.
  5. List the sequence of events and the reason for each. Repeat steps 1-3, as desired.

Data and Observations
Sequence the events that you observe.

  1. _____________________________________________
  2. _____________________________________________
  3. _____________________________________________
  4. _____________________________________________
  5. _____________________________________________

Questions
Use your knowledge of the gas laws and the principles of combustion to explain the observations listed above.

Teacher’s Notes

  1. The correct sequence of events would be:
    a. The volume of gas in the jar will expand.
    b. Some condensation may form on the glass.
    c. The candle will go out.
    d. The water level will rise as the hot gasses cool.
  2. The explanation of the events is:
    a. As the candle burns, the gas above it is heated and, therefore, expands.
    This behavior is stated in the gas law known as Charles’ s Law.
    b. Condensation is a product of the combustion reaction and can be formed when the warm, moist gas comes into contact with the cool, glass surface.
    c. Combustion reactions require the presence of oxygen. When the candle has reacted with all of the available oxygen, the candle will go out.
    d. After the reaction has ceased, the heat from the combustion is no longer produced. Therefore, the gas cools and contracts. The water then returns to the jar. This behavior is stated in the gas law known as Boyle’s Law.
  3. Students must use dry candles and glassware to be successful. You may want to have towels and extra candles on hand.
  4. When this is done as a demo (with a glass pie pan), the jar will rattle at first. This gives evidence that expanded, hot air is escaping in the jar.

Diposal
All solid materials may be placed in the trash can, and the liquids may be poured into the sink.