Dissolved Gasses and Temperature References

Name: Patrick
Status: other
Grade: other
Location: NH

Question: Is the relationship between the level of dissolved oxygen
in water and other gases a constant at a given temperature and
pressure? If you can not answer this question or will not because I
am not a teacher or K-12 student, can you at least point me in the
direction of a good reference that treats the subject of dissolved
gases and measurement of such.
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Patrick,

The factors that affect solubility of gases are: temperature (the higher 
the temperature, the lower the solubility - gases tend to escape more if 
they are moving faster), pressure (the higher the pressure, the higher 
the solubility - gases tend to stay in the liquid if it is forced into 
the liquid), the type of molecules involved (the more similar in 
intermolecular attractive force, the higher the solubility). Since we 
are talking about one particular solvent (water) and one particular 
solute (oxygen), then only the external factors of temperature and pressure 
are variable. Thus, yes, given one pressure and one temperature, there 
should only be one level of solubility.

Greg (Roberto Gregorius)
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Your age and student/teacher status are no impediment for us to respond
to appropriate inquiries such as yours. At a constant temperature and gas
pressure the concentration of a gas dissolved in a liquid is constant -- 
provided -- that the gas does not undergo some chemical reaction. For
example, the concentration of dissolved carbon dioxide (CO2) would also
depend upon the pH, in addition to temperature and the pressure of CO2. The
law governing the solubility of gases is called Henry's Law, which states
that the gas pressure "P" is proportional to the concentration in the
solvent "C".  Explicitly: P = K x C, where "K" is a temperature dependent
constant that must be determined by experiment. You can find tabulations of
"K" in many chemical texts and handbooks, or on the internet if you do a
search on "Henry's Law" or "Henry's Law constants". The website:
http://en.wikipedia.org/wiki/Henry's_law gives a reasonably detailed
discussion of Henry's law.  Some warnings: The numerical value of "K"
depends upon the units of pressure, P, and concentration, C, so you have to
be careful to use a consistent set of units compatible with the tabulation
of values of "K". The values of "K" found in tabulations are almost always
taken from an extrapolation of "P" vs. "C" to zero concentration. At high
concentrations, which is equivalent to high pressures, Henry's law constant
"C" is no longer "a constant" in non-ideal combinations of gas and solvent.
Another interesting "fact" is that the solubility of all the common gases
decreases with increasing temperature. I don't know of any exceptions.
Finally, Henry's law has been "dusted off". For many years the only place
one encountered Henry's law was in chemistry texts. More recently, however,
it has been found useful in the fields of geophysics and astrophysics to
"model" the "solubility" or gases in molten lava etc.

See, NEWTON will try to answer interesting questions from any source.

Vince Calder
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