Boiling Cold Water

A vacuum pump is used to reduce the ambient pressure above water under a sealed bell jar. By reducing the pressure, the boiling point is lowered so that the water begins to boil at room temperature. 

Curriculum Notes 

This demo would be appropriate for an introductory chemistry course when states of matter are being discussed. Also, this demo could be used to illustrate vapor pressure and the thermodynamics of phase changes. Projection of the demo is optional but recommended.

Lead Time 
One day of lead time is required for this project.
Discussion 

A liquid boils when the vapor pressure of the liquid is equal to the ambient pressure. When the ambient pressure is reduced to below the vapor pressure of the liquid, the liquid boils. Water typically boils at 100 degrees celsius when the pressure is equal to 1atm, but when the pressure is reduced using a vacuum pump, the water boils at room temperature.

Materials 
  • 150mL warm water in a 250mL beaker
  • vacuum pump
  • bell jar
  • water/desiccant trap
  • vacuum hose
  • vacuum plate
  • rubber gasket
  • blast shield
Procedure 

Place a 250mL beaker containing 150mL of warm water on a vacuum plate. Cover the beaker on the plate with a bell jar. Connect the vacuum pump to the plate with a vacuum hose. Turn on the vacuum pump to reduce the pressure inside the bell jar. As the pressure is reduced, the water begins to boil.

Safety Precautions 

Use blast shield for protection in case of glass implosion due to vacuum. Break the vacuum seal prior to turning off the vacuum so that vacuum oil does not get sucked up the hose.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group