Re: CO2 Bends
"Olive K. Charlsey" writes:
>CO2 does dissolve in water to form H+HCO3-. There is no other way that it
>dissolves, no matter what pressure, no matter what the concentrations.
Actually, pressure has a significant effect on the solubility of CO2. This
fact is clearly demonstrated every time you open a bottle of soda.
>When the "CO2 laden water" comes out of the filter, it has a higher
>concentration of carbonic acid (H+ HCO3-) since there is no difference
>between dissolved CO2 and carbonic acid.
This is a fairly common misconception which is perpetuated, IMO, by the over
simplifications used by many introductory chemistry texts.
There is a difference between "dissolved CO2" and carbonic acid. When CO2 is
added to water it initially forms a loosely hydrated species denoted CO2(aq).
This dissolved molecular CO2 reacts _slowly_ with water to form carbonic acid,
CO2(aq) + H2O = H2CO3(aq)
Furthermore, this kinetically slow reaction does not go to completion. At
equilibrium, only a small fraction (ca. 0.2%) is actually converted to
carbonic acid. Most of the CO2 remains as solvated molecular CO2. In fact,
the pKa most often reported for carbonic acid (pK1 = 6.38) is not really the
true pKa of carbonic acid. Rather, it is the pKa of the equilibrium mixture
of CO2(aq) and carbonic acid. Carbonic acid itself is actually a much
stronger acid than this, with a true pK1 value of 3.58.
As for this business about "CO2 bends"... I think that if one actually thinks
about how an organism gets the bends, it's pretty clear that it ain't gonna