Carbon dioxide ionization constant

The concentration of tme carbonic acid (H2CO2) is negligible in comparison to dissolved carbon dioxide, eg, only 0.3% of the latter is hydrated to carbonic acid at 25°C. The ionization constant is a composite constant representing both the CO2 hydration reaction, iC, and ionization of tme H2CO2, ifj = ifjj QQ /(I + K). Temperature-dependent equations for and are (29)... 

Carbon dioxide, the final oxidation product of carbon, is not very reactive at ordinary temperatures. However, in water solution it forms carbonic acid [463-79-6] H2CO2, which forms salts and esters through the typical reactions of a weak acid. The first ionization constant is 3.5 x 10 at 291 K the second is 4.4 x 10 at 298 K. The pH of saturated carbon dioxide solutions varies from 3.7 at 101 kPa (1 atm) to 3.2 at 2,370 kPa (23.4 atm). A soHd hydrate [27592-78-5] 8H20, separates from aqueous solutions of carbon dioxide that are chilled at elevated pressures. 

Tbe ionization constants listed are calculated assuming that all the carbon dioxide that dissolves is in the form of H2CO3. 

Hamed, H. S. and Davis, R. The ionization constant of carbonic acid in water and the solubility of carbon dioxide in water and aqueous salt solutions from 0 to 50, J. Am. Chem. Soc. 2030-2037 (1943). 

Determination of the catalytic activity of the hydroxyl ion is difficult, because the mutarotation becomes too rapid for accurate measurement when the concentration of hydroxyl ions rises above 10 /unolar. With a minute concentration of hydrogen ions, accurate measurements require rigorous exclusion of carbon dioxide and other impurities. Evaluation of the rate constant is also complicated by ionization of the sugar, a subject that was not considered by the early workers. 

Liquid carbon dioxide is a non-polar (non-ionizing) solvent, in many ways like hexane. However, in the supercritical phase the dielectric constant of CO2 increases with increasing pressure. ( ) The dielectric constant is an indicator of the polarity of the SCFCO2 solvent [Figure 4]. Thus, by controlling pressure (or the addition of a polar cosolvent), the selectivity of SCF can be fine tuned for the preferential extraction of the compounds of interest based on their polarity. 

The laboratory will focus on the operational aspects of pH measurement. It is appropriate that we start this course with pH because this parameter is so fundamental to the physical-chemical phenomenon that occurs in aqueous solutions. The pH of a solution which contains a weak acid determines the degree of ionization of that weak acid. Of environmental importance is an understanding of the acidic properties of carbon dioxide. The extent to which gaseous CO2 dissolves in water and equilibrates is governed by the Henry law constant for CO2. We are all familiar with the carbonation of beverages. The equilibrium is... 

Carbon dioxide is a slightly stronger acid in solution than hydrogen sulfide. Its ionization constant for the first step ionization to and HCOs is approximately 4 x 10" at 25 C compared to 1 x 10 for the corresponding hydrogen sulfide ionization. As a result, under... 

However, at the low values of jCco2 for pco2 P to 1 atm, the Xqo2 and Ncoz values are almost coincident (see Table 10). The % CO2/P002 P ot of these workers does not clearly show curvature, but there is a variation of H values which could be interpreted as a bend around the low end of the pco2> i e., % CO2 - 0. It was concluded that practically all the carbon dioxide exists as free carbon dioxide. Olson and Youle stated that the following value for K is accepted by most chemists as the first ionization constant of aqueous carbonic acid ... 

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