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1997
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Chemical Education Today
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Letters
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The authors reply to "The Joys of Liquid Nitrogen"
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William T. Nolan and Thaddeus J. Gish
Oakland Community College, Waterford, MI 48327-4187
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June 1997
Vol. 74 No. 6
p. 617
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| Full Text |
The authors reply to Blatchley.
We thank Ronald C. Blatchley for his interpretation
of experiment 3, "The Mysterious Liquid Drop", and for
pointing out that the drop is a mixture containing nitrogen
as well as oxygen. The liquid drop that forms at the bottom
of the tube has a temperature of about -196 °C, the
temperature of the boiling liquid nitrogen used to cool the tube.
The air in the tube above the drop is very cold, and contains
a large number of gaseous nitrogen and oxygen
molecules having low kinetic energies and low molecular speeds.
In addition, the density of the air above the drop is high
relative to the warmer air outside of the tube, and the
frequency of collision of gaseous nitrogen molecules with the
drop's surface is high. Therefore, a significant number of
gaseous nitrogen molecules would be expected to condense at
the surface of the drop and be retained by dispersion forces.
In addition to nitrogen and oxygen, we would expect the
drop to contain other condensed substances such as argon
and traces of higher-boiling noble gases. Argon would boil
at -183 °C, prior to the oxygen boiling at -183 °C, as the
tube is allowed to warm.
The chemical behavior of the burning wood splint
described in Blatchley's experiment is precisely what we
observe when experiment 4, "A Familiar Chemical
Change", is performed. Timing is indeed important. The
glowing splint is extinguished if the test tube containing the drop
is not allowed to warm in air for a short time. However, if
we first warm the tube in the air for a few seconds and
then insert the splint, the splint bursts into flame. His
interpretation nicely explains these observations.
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| More Information |
 Citation |
Nolan, William R.; Gish, Thaddeus J. J. Chem. Educ. 1997 74 617.
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Keywords |
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History |
Created:
Last Updated: |
July 28, 1999
June 23, 2005
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Link to Letter added (May 2004).
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June
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