NEW ZEALAND PHYSICS TEACHERS' RESOURCE BANK

Cold as Neptune: Solid Nitrogen

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Frozen nitrogen after pumping for a while.

Apparatus Sketch
Abstract

Pumping on liquid nitrogen causes it to freeze.

Portable Yes
Principles Illustrated

As the vacuum chamber is pumped, the most energetic molecules of nitrogen, those in the vapour phase, are removed. Thus the average energy per molecule is lowered and the temperature is lowered. The liquid nitrogen boils rapidly as it cools and actually freezes, forming snow-like solid nitrogen.

NCEA & Science Curriculum
Teacher Guide
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Video
Instructions

Put a small amount of liquid nitrogen in a small beaker. Be sure to use a layer of insulating foam, and a black background (just black paper) is helpful. Pump. Nitrogen will boil rapidly. Solid will form and melt repeatedly, and finally form and remain solid. With use of a video camera this demo is suitable for a large lecture theatre. We have found a video camera pointed at the apparatus with image displayed on a data projector to be very effective. The video camera seems to work best pointed at the side and angled down somewhat with our particular vacuum desiccator. Larger sketch || Apparatus Front || Apparatus Side || Apparatus close up

Diagram of apparatus
Safety

 

Be sure to use a fairly large chamber that can withstand cooling. Be sure to insulate the bottom of the liquid nitrogen beaker from the base of the vacuum chamber. Be sure to use a sturdy vacuum chamber and keep students at some distance. We have found a video camera pointed at the apparatus with image displayed on a data projector to be very effective. The video camera seems to work best pointed at the side and angled down somewhat with our particular vacuum desiccator.

Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
Related Resources
References

PIRA 4C20.40

UT-Austin Version

Credits

This teaching resource was developed by the Te Reo Māori Physics Project with support from

 

  • This resource was developed by the Te Reo Māori Physics Project.
  • The New Zealand map shown on the poster frame above is used with permission from www.nz.com.
  • The image of Neptune is from NASA, Courtesy NASA/JPL-Caltech.
  • This teaching resource was developed in collaboration with Mabel Stewart, a New Zealand Science, Mathematics and Technology Teacher Fellow, 2008, hosted by Victoria University School of Chemical and Physical Sciences. Mabel teaches at Bishop Viard College in Porirua, New Zealand. See NZSMT Teacher Fellowships for more information about the Teacher Fellow Programme.

Copyright

Copyright and fair use statement