Reply To: The Random Post Thread (Game Potential)

[mtgordon]

waste CO₂ from the muscles and extremities is carried to the lungs as carbonic acid, which converts to gaseous form when exposed to open air in the lungs

This is an oversimplification. The CO₂ is bound to hemoglobin on the way out. The way hemoglobin selectively binds CO₂ and O₂ so as to serve as a transport molecule for both gases is interesting, but it’s quite complicated. If there’s sufficient interest, I can go into detail.

Carbonic acid is only stable as a gas at one atmosphere and room temperature.

I’ve only ever heard of carbonic acid existing in aqueous solution, not as a gas. Wikipedia backs me up on this.

It all boils down to Le Chatlier’s principle. You can carbonate water by bubbling CO₂ through it under pressure. Solvation will reduce the volume of the system (since CO₂ in solution takes up much less space than the corresponding gas), and the resultant decrease in pressure helps shift the equilibrium. I suspect that higher pressures yield more favorable kinetics, i.e the process goes faster. In the resulting closed bottle of soda, held at roughly the final pressure, there’s an equilibrium between dissolved CO₂, H₂CO₃ (carbonic acid), HCO₃^– (hydrogen carbonate, aka bicarbonate, ion), CO₃^-2 (carbonate ion), and gaseous CO₂ in the small pocket of air between the soda and the cap. You can get away with a lower pressure, so long as the bottle is kept sealed and there isn’t much gas in the container. An open bottle of soda loses its CO₂ to the atmosphere because the small air pocket suddenly becomes immense, and the equilibrium is shifted strongly toward dumping CO₂ up and out.

The real reason you don’t want to carbonate beverages using baking soda and hydrochloric acid is the NaCl product. It’s not really palatable in large quantities.