Science Area: Chemistry                                                        Concept: Atmospheric Pressure

                                                                                                                Boiling Point

                                                                                                                Cooling a Gas

The Collapsing Can

Paradox #2

Materials:

• An empty aluminum soft drink can
• A hotplate
• A pair of tongs
• Water
• A large beaker/bowl or saucepan

Safety Considerations:

• Be careful not to burn yourself when using the hotplate.
• Be careful not to trip over anything when conducting this experiment.

Discrepancy:

Many students may not believe that by boiling water inside a can and then transferring it to cold water will cause the can to crush.

Procedure:

1. Fill the beaker with cold water
2. Put approx. 20 mL of water into the empty soft-drink can
3. Heat the can on a hotplate until the water in the can begins to steam
4. Allow the water to continue boiling for another 30 seconds
5. Using the tongs, grasp the can and quickly invert it and place the mouth of the can into the beaker full of water
6. Observe what happens

Questions:

1. What happens to the can when it is boiling on the hotplate?
2. What happens to the water inside the can when it is on the hotplate?
3. What happens to the can when it is moved to the cold water?
4. Why does this happen?
5. What is this process called? What does this name mean?

Explanation:

Boiling water inside the can filled the can with water vapor, which was cooled suddenly when inverted into cooler water.  Cooling the can caused water vapor in the can to condense, creating a vacuum and causing the pressure outside the can to be greater then inside and therefore crush the can.

Source:

            Shakhashiri, Bassam Z. Chemical Demonstrations: A Handbook for Teachers of

            Chemistry, The University of Wisconsin Press. Madison, Wisconsin. 1997, p. 20