Collapsing Can

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Page ID: 128800

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Required Training	Required PPE
UC Lab Safety Fundamentals	Lab coat, safety glasses/goggles, nitrile gloves

Equipment	Chemicals
Beaker Tongs
Soda cans
Hot plate
DI water squirt bottle
Ice
Ice pan

Procedure:

Add approximately 100ml of water into the soda can and heat it on a hot plate.
Prepare and ice/water bath in an aluminum pan.
Once a steady stream of steam is coming out of the can, lift it with the beaker tongs and quickly dunk it upside-down into the ice/water bath.
NOTE: do not heat the can until all the water has evaporated.
In a couple seconds the can will collapse.

Discussion:

This demonstration shows the power of phase changes. As a gas, the water vapor occupies a volume much larger than it does as a liquid. This follows the equations written below:

At room temperature: P_in = P_out= 1 atm

P_in= 1 atm = P_air + P_vapor = 0.972 atm + 0.028 atm

The vapor pressure of H₂O at room temperature can be found in your textbook

At boiling point: P_in = P_out= 1 atm

P_in = 1 atm = P_air+ P_vapor = 0 atm + 1 atm

The definition of boiling point

As this low density water vapor condenses on the walls of the cold soda can, a vacuum is created following a similar equation:

P_in ≠ P_out

P_in= P_air + P_vapor = 0 atm + 0.028 atm

P_out = 1 atm

P_out>> P_in

Even though only a small amount of water vapor is contained in the can when the can is dunked into the ice bath, a number of properties of this demonstration are dvantageous in demonstrating a phase change. The aluminum can is highly conductive and quickly cools to a level at which the vapor condenses. The can is weak and crushes easily under pressure. The opening of the can is small enough to not let air rush in while the can is being flipped—the more water vapor in the can (displacing air) the more the pressure change will be when the vapor is condensed.

Hazards:

Exercise caution when using a hotplate.

SOP:

N/A

Disposal (by Storeroom)

Return all materials to the storeroom. No disposal should be needed.