Science Concept:Pressure. Air travels from an area of greater pressure to an area of lesser pressure.

Materials:
* Pie dish
* 200 mL of water
* food color (any color)
* one candle
* match or lighter
* long neck 500 mL florence flask

Directions:

* Mix the 200 mL of water with the food coloring and then pour the mixture into the pie dish.
* Take a candle with clay dough to support it and place it in the middle of the pie dish filled with the food coloring and water.

* Let candle burn for a few minutes, and then place 500 mL florence flask over burning candle.

* Watch the candle flame go out and the water move up into glass flask.

Alternative: Is is really necessary to have a combustion reaction to make this demo work? For many years an erroneous explanation cited that the water came into the flask as a result of using up the oxygen. Less gas, less pressure, water comes into the jar. In recent years, several articles have been published which state that this explanation is incorrect. Can we prove it?

Do you really need the candle for this demo to work? Heat the empty florence flask on a hot plate for about 5 minutes first. Do not use the candle and simply invert it on the pie plate of the water.

Introduction:

Have you all ever seen a magic trick performed? Well I am going to show you one of my special magic tricks.

Explanation:

While the candle burns it is using the oxygen that is found inside of the flask, it is heating and expanding the air inside of the flask. Some of the air molecules are forced out of the flask. After the candle goes out the source of heat is removed. The gas molecules now cool. As a result of less air molecules ( oxygen and nitrogen) and the cooler temperatures found in the glass flask, this causes the air pressure inside to decrease. The decreased pressure is due to the fact that there are less gas molecules and slower gas molecules inside which cause less collisions, causing less pressure. This allows the greater air pressure outside of the glass flask to push the water into the flask and then balance out the pressure.

Reaction: candle wax burning using up oxygen

C₂₂H₄₄ + O₂ ----> CO₂ + H₂O + Energy

Safety: Do not play with matches and fire. Do this with adult supervision.

Disposal:

Reference: Public Domain

Shakhashiri, B, Chemical Demonstrations, vol. 2, U. of Wisconsin Press, 1985,p. 158

Krnel, Dusan; Glazar, Sasa A. "Experiment with a Candle" without a Candle J. Chem. Educ. 2001 78 914. (July 2001)

Birk, James P.; Lawson, Anton E. The Persistence of the Candle-and-Cylinder Misconception J. Chem. Educ. 1999 76 914. (July 1999)