Hi tc_topcat!!
Polar gases dissolve in water easily like polar liquids do, non-polar
gases which dissolve in water do it so by two ways:
· reacting to form polar products (CO2) or
· by dipole-induced dipole interactions (O2).
The oxygen molecule O2 cross the air/water interface in a slow
process. The speed of the dissolution process depends on whether the
water is still or running, how much surface is in contact with the
air, what is dissolved in the water, and whether any films (like soap,
or oil ,etc.) are floating on the surface. Once the oxygen crosses the
air/water interface, it is caged by water molecules by weak dipole
induced forces:
"How oxygen dissolves:
Water, as a polar molecule, induces an accumulation of electron
density (dipole moment) at one end of non-polar gas molecules such as
oxygen (O2 ) and carbon dioxide (CO2 ). ... The electron cloud of O2
is normally distributed symmetrically between the bonded O2 atoms.
When the negative end of the H2O molecule approaches the oxygen
molecule, the electron cloud of the O2 moves away to reduce the
negative-to-negative repulsion. A dipole (a molecule with positive and
negative charges separated by a distance) results in the nonpolar O2
molecule and causes O2 and H2O to become weakly attracted to each
other. This intermolecular attraction between the oppositely charged
poles of nearby molecules is termed a dipole-dipole force. The
creation of these forces explains the mechanism by which gases
dissolve in water."
From "The Chemistry of Oxygen Solubility Reading" at Water on the Web site:
http://waterontheweb.org/curricula/bs/student/oxygen/reading.html
At the above reference you will find additional info, so I suggest you
to visit that page.
Water on the Web also brings animations that help to understand the
oxygen solubility in water. The animations require the Flash plug-in.
If you are not able to view the animations, please download the
plug-in at:
http://www.macromedia.com/shockwave/download/.
"Induced Dipoles" animation:
http://waterontheweb.org/curricula/bs/student/oxygen/shock2.html
"Oxygen Solubility: Henry's Law" animation:
http://waterontheweb.org/curricula/bs/student/oxygen/shock1.html
Additional resources at this site can be found at PROCEDURES section
of the page "Teaching about the Chemistry of Oxygen Solubility":
http://waterontheweb.org/curricula/bs/teacher/oxygen/teaching.html
The following text give us more info about polar molecules and induced
dipoles forces:
"We can also have the attraction of a dipole for a molecule that is
ordinarily not a dipole. When a dipole approaches a nonpolar molecule,
its partial charge either attracts or repels the electrons of the
other particle.
For instance, if the negative end of the dipole approaches a nonpolar
molecule, the electrons of the nonpolar molecule are repelled by the
negative charge. The electron cloud of the nonpolar molecule is
distorted by bulging away from the approaching dipole as shown in
Figure 14-3.
As a result, the nonpolar molecule is itself transformed into a
dipole. We say it has become an induced dipole. Since it is now a
dipole, it can be attracted to the permanent dipole.
Interactions such as these are called dipole-induced dipole forces. An
example of this force occurs in a water solution of iodine. The I2
molecules are nonpolar while the water molecules are highly polar. The
case of two nonpolar molecules being attracted must also be taken into
account.
For instance, there must be some force between hydrogen molecules;
otherwise it would be impossible to form liquid hydrogen. Consider a
hydrogen molecule with its molecular orbital including both nuclei. We
know intuitively that the electrons occupying that orbital must have a
specific location. If they are both away from one end of the molecule
for an instant, then the nucleus is exposed for a short time.
That end of the molecule has a partial positive charge for an instant;
a temporary dipole is set up. For that time, the temporary dipole can
induce a dipole in the molecule next to it and an attractive force
results as shown in Figure 14-4. The forces generated in this way are
called dispersion forces."
From "Polar Molecules" at San Lorenzo Valley High School site:
I suggest to visit this page to see the figures and further reading.
http://cougar.slvhs.slv.k12.ca.us/~pboomer/chemtextbook/cch14.html
Additional references related are:
"Intermolecular Forces and Solutions":
http://employees.csbsju.edu/hjakubowski/classes/Chem%20of%20Disease/IMF_Solutions/olIMF_solutions.htm
"Intramolecular Forces (intra means within)":
http://jhss.wrdsb.on.ca/library/html/assignments/science/bond2.htm
"Definition of London forces":
http://www.wordiq.com/definition/London_forces
"Henry's Law and the Solubility of Gases":
http://www.psigate.ac.uk/newsite/reference/plambeck/chem2/p01182.htm
"Why does the solubility of gases usually increase as temperature goes down?"
http://antoine.frostburg.edu/chem/senese/101/solutions/faq/temperature-gas-solubility.shtml
"How can I predict oxygen solubility in water?"
http://antoine.frostburg.edu/chem/senese/101/solutions/faq/predicting-DO.shtml
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Search strategy:
"how oxygen" dissolved
gas dissolved water
dipole force gas dissolved
Induced Dipoles water oxygen
"induced dipole" oxygen water solution
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I hope that this helps you. Plesar use the clarification feature to
request clarifications if you find something unclear or incomplete
before rate this answer. I will gladly give you further assistance on
this.
Best regards.
livioflores-ga |
