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DemonstrationsProperties of Gases 10.2

Lecture Demonstrations

Properties of Gases

10.2 Liquid Nitrogen and Charles’ Law

Subjects: Behavior of gases, ideal gas law, Charles’ Law

Description: Various experiments are performed with liquid nitrogen.

Materials:

  • Small balloons (water balloon size or long narrow balloons)
  • Regular size balloon
  • Shallow dish (use crystallization dish on prep shelf)
  • Liquid nitrogen in a dewar◊
  • Insulating gloves
  • Tongs for handling balloons
  • Small Tupperware container
  • Racquet ball (optional)
  • Fruit or vegetable to freeze – flower, parsley works well (optional)◊
  • Optional: Vernier Thermocouple, interface, and Logger Pro or Logger Lite software.

◊Advanced prep item: Get LN2 ahead of time. Instructor to provide parsley or flower.

*Located in the drawers opposite the bin storage shelves.

Pre-Class Prep:

  1. Blow up balloons (at least 5-7) and immerse in liquid nitrogen.
  2. Blow up regular sized balloon to fit in crystallization dish. You can also use the dewar with the wider mouth for larger balloons.

Procedure:
Demo 1:

  1. Place one last balloon in the dewar with the other balloons.
  2. Remove all balloons like a magician’s hat and allow to inflate.

Demo 2:

  1. Put the regular balloon in the crystallization dish.
  2. Pour liquid nitrogen over the balloon. Remove from cold and allow to inflate.

Demo 3:

  1. Place parsley or flower in dewar for ~1 minute.
  2. Smash on bench top. (Repeat with racquet ball if desired)

Demo 4:

  1. Fill Tupperware half way with liquid nitrogen.
  2. Cap with lid, Tupperware lid will pop off.

Discussion:

Charles’ Law describes the relationship between temperature and volume. If a given quantity of gas is held at a constant pressure, its volume is directly proportional to temperature. The relationship is given by the equation below:

V = Cc x T

Where Cc is a proportionality constant.

The temperature of liquid nitrogen is 77K (-196°C or -321°F). When an object is immersed in liquid nitrogen, it freezes rapidly and becomes brittle, allowing it to break easily.

When the liquid nitrogen is poured into a container and sealed, the rapid evaporation of the liquid creates a high pressure in the container, causing the lid to pop off.

Safety:

Liquid nitrogen is extremely cold and can cause hypothermia or burns. Use insulating gloves and safety glasses while performing the demonstration.

References:

1. Prof. Botch
2. Oliver-Hoyo, M., Switzer, W. L. J. Chem. Educ. 2005, 82, 251.
3. NCSU Department of Chemistry Lecture Demonstration website: http://www.ncsu.edu/project/chemistrydemos/DemoList.html
4. University of Illinois at Urbana-Champaign Chemistry department Lecture demonstration web site: http://www.chem.uiuc.edu/clcwebsite/gases.html


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