Rising Water (Kimberly Tafoya)

Root question:

The flame will go out due to the lack of oxygen, what caused the water to rise?, etc.

Procedure:

Rising water: Take a birthday candle and heat the bottom until the wax just begins to melt. At this time try to place the birthday candle at the bottom but in the middle of a large beaker or wide-mouth glass cup. (Alternatively you can use a piece of clay to hold the candle to the bottom.) Take a 50mL or 100-graduated cylinder and have it ready in hand. With your wash bottle, add enough water to the container holding the candle such that the level of the water is halfway up the candle. Add food coloring to the water to see the water better. Light the candle, wait for 15 seconds so the flame is burning strong and then place the graduated cylinder over the candle and have it rest on the beaker/ glass cup. Watch as the water begins to raise inside the inverted graduated cylinder almost defying gravity. Write your observations.

Target response:

The evaporation of the water to water vapor as the candle burns, and the cooling that occurs when the candle goes out, cause lower air pressure inside the glass than outside. The water is pushed into the glass until equilibrium is reached.

Common Misconceptions:

Some students might mention that a vacuum is created inside the glass by the burning candle, which sucks the water up. That would mean that there was no air in the glass whatsoever. If that were the case, the higher outside air pressure would immediately implode the glass. Since this does not occur, students should conclude that a vacuum is not the cause of the rising water in the glass.

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