The kinetics of the carbon dioxide-carbonic acid reaction

Abstract

In aqueous solutions of Carbon Dioxide, the concentration of dissolved C02 as such, is, at equilibrium, far greater than the concentration of carbonic acid, [H2C03]. On this account solutions of carbon dioxide are found to be only weakly acidic, although H 2C03 itself, according to THIEL,* and THIEL and STROHECKER and later authors, is a fairly strong acid, with a true first ionization constant of about 2 X 10“4, i.e ., 2 X 10~4 [H2C03] = [H] [HC03]. The “ apparent” first ionization constant of carbonic acid, KCo2> is, however, given by the equation Kcp2 (dissolved [C02] + [H2C03]) = [H] [HODS], and since the dissolved [C02] at equilibrium is found to be of the order of 1000 times greater than the [H2C03], the value of KC02 is correspondingly smaller than 2 X 10~4, and is given as 3 X 10~7. MCBAIN, THIEL ( loc. cit. ) and others have shown that the reversible reaction C02 -f- H 20 0 H 2C03 is a relatively slow one, and hence that the neutralization of dissolved carbon dioxide by alkali differs from the neutralization of other weak acids in not being instantaneous.