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:
- Blow up balloons (at least 5-7) and immerse in liquid nitrogen.
- 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:
- Place one last balloon in the dewar with the other balloons.
- Remove all balloons like a magician’s hat and allow to inflate.
Demo 2:
- Put the regular balloon in the crystallization dish.
- Pour liquid nitrogen over the balloon. Remove from cold and allow to inflate.
Demo 3:
- Place parsley or flower in dewar for ~1 minute.
- Smash on bench top. (Repeat with racquet ball if desired)
Demo 4:
- Fill Tupperware half way with liquid nitrogen.
- 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