Triple Point of Water, 4C50.40

Topic and Concept:

• Change of State, 4C50. Critical Point

Location:

• Cabinet: Thermodynamics (TD)

• Bay: (A5)

• Shelf: #2

Abstract:

A sealed Erlenmeyer flask filled with ice water has the air pumped out of it creating a partial vacuum. Thus brings the mixture to the triple point of water whereupon the mixture boils showing solid, liquid, and gas existing at the same pressure and temperature.

Important Setup Notes:

• Ice is needed of this demonstration, witch may require extra setup time.

Setup and Procedure:

1. Pull out and plug in the Vacuum Pump cart. See Vacuum Pump page for operational instructions.

2. Add about an inch worth of ice to either flask.
3. Add just enough water to the flask to cover the ice.
4. Firmly push on the stopper with the vent tube to seal the flask.
5. Place the vacuum hose onto the vent tube.
6. Turn on the vacuum pump.

Cautions, Warnings, or Safety Concerns:

• N/A

Discussion:

Matter exists in different phases depending upon its pressure and temperature. The specifics depend on which substance we're considering. The combinations of temperature and pressure that lead to a given phase of matter can be summarized in a phase diagram. Such a diagram for water is shown above. There exists one particular combination of temperature and pressure that allows water to exist as a solid, liquid, and gas simultaneously. This is called the triple point and for water this pressure and temperature are 612 Pa and 0°C. Adding ice to the water brings the ice water mixture into a dual phase state at 0°C. Using the vacuum pump, we pump out air from the flask which causes the internal pressure to drop. Upon reaching a pressure of 612 Pa, we see the ice water boil.

Videos:

• Lecture Demonstration's Youtube Channel

References:

• Wikipedia - Triple Point

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