A Study of the System Carbonic Acid, Carbon Dioxide and Water

Abstract

ALTHOUGH the quantitative equilibrium relations in the bicarbonate-carbonic acid systems are very accurately known in biological solutions, it is a remarkable fact that only little is known about the way in which this equilibrium is attained and about the velocities of the reactions occurring. Still it might be supposed that this equilibriuim is not reached at once, as in purely ionic reactions, but that it is a very definite time-process under certain conditions. Thus the buffer-capacity of a bicarbonate system, after addition of a stronger acid, is calculated from the apparent dissociation-constant (k1 = 3 x 10-7), but it is possible that initially the system is reacting according to the true constant of carbonic acid (k1 = 4 x 10-4) during a biologically significant time, with a consequent large temporary increase of the resulting cH. If the carbonic acid were produced continuously, it might then be acting continuously as a strong acid.

Reply to the ‘Comment on “Nickel nanoparticles catalyse reversible hydration of carbon dioxide for mineralization carbon capture and storage”’ by D. Britt, Catal. Sci. Technol., 2013, 3, DOI: 10.1039/C3CY00142C

“…Therefore, the lack of difference in equilibrium constants in stopped-flow results is due to two possibilities: firstly, that the pH range during the reaction is below 4.9 and therefore the catalytic activity is dominated by H + ions [14][15][16] (see ESI † for details) and that the NiNPs are poisoned by the phenolphthalein indicator because oxygen (active site of phenolphthalein) has a higher binding energy than hydroxyl groups chemisorbed at the Ni surface 17 so they are hard to remove.…”

Hydrogen-Bonding Structure and Dynamics of Aqueous Carbonate Species from Car−Parrinello Molecular Dynamics Simulations

“…Despite the importance of aqueous carbonate species, surprisingly little is known about their structural environments and dynamical behavior in aqueous solution. It has been known for many decades that when CO 2 dissolves in water, about 1% of it converts to carbonic acid, H 2 CO 3 . , It is also well-known that aqueous carbonic acid deprotonates to bicarbonate, HCO 3 − , and carbonate, CO 3 2− , with p K a values of 6.4 and 10.3, respectively. Direct spectroscopic data for H 2 CO 3 date from the early 1990s, and there is more recent spectroscopic evidence for its presence on calcium carbonate surfaces. , Carbonic acid can be synthesized by irradiation of frozen films of CO 2 /H 2 O mixtures with high-energy He ions or protons , and by protonation of HCO 3 − /CO 3 2− solutions at low temperatures .…”

The hydration structure of dissolved carbon dioxide from X-ray absorption spectroscopy

“…The solubility of gaseous CO 2 is governed by Henry's Law under equilibrium conditions (k H = 3.38 × 10 −2 mol L −1 atm −1 ), with normal average CO 2 pressures in the atmosphere (3.9 × 10 −4 atm) yielding total dissolved CO 2 concentrations of 1.33 × 10 −5 M in pure water [14]. Most of this is present as the weakly hydrated CO 2 molecule, but a small fraction (∼1%) hydrolyzes to form the short-lived carbonic acid (H 2 CO 3 ) molecule, which subsequently forms bicarbonate, and carbonate ions via proton transfer reactions [15][16][17].…”