Rate of Hydration of Carbon Dioxide and Dehydration of Carbonic Acid at 25°

Abstract

Although the full evidence for this scheme is not yet available, it is clearly more general than the “classical” reaction scheme (see e.g. Edsall and Wyman (5)), which assumed that k13 = kal = 0. The constants klz and ks, are very large, k12 probably being of the order of 5 x lOlo ~hl se@, and kzl of the order of 107 see-1 (3). The absolute values of these velocity constants do not concern us further here; their ratio must be equal to the true ionization constant of H2COa, which we denote as KHrCOr. This is reported as 1.72 X 10-’ M at very low ionic strength by Wissbrun et al. (6). The dependence of KEIco, on ionic strength has not been measured ; we will assume it to be similar to that of acetic acid. The ratio (H2C03) : (COz) at equilibrium is very small ( < 0.002)) and at all pH values in our experiments, the ratio (H&OJ: (HC03) is 0.005 or less. Therefore, H&O* can be neglected in the over-all reaction, which we can write as