Activity coefficients of bicarbonates and carbonates in seawater1

• Main Author: R. M. Pytkowicx
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Carbonic acid
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.507.2064; http://www.aslo.org/lo/toc/vol_20/issue_6/0971.pdf

The total (stoichiometric) activity coefficients of bicarbonate and of carbonate ions were determined in seawater by a method that is independent of ion-pairing models and used in conjunction with estimates of the coefficients of major cations to calculate the mean activity cocfficicnts of bicarbonate and carbonate salts. The total ( stoichiometric) activity coef-ficients of bicarbonate and of carbonate ions in seawater were dctcrmined as a func-tion of the salinity from the ratios of the thermodynamic and the apparent dissocia-tion constants of carbonic acid. This method made it unnecessary to resort to ion-pairing models and, thus, permitted the avoidance of many assumptions. The coefficients were used in conjunction with estimated ones for some of the major ca-tions of seawater, introducing at this stage specific ionic interaction models, to calcu-late the first reported values of the mean activity coefficients of bicarbonate and of carbonate salts in seawater. Data on single ion and mean activity coefficients are of use in physicochemical studies such as the interpretation of the solubility behavior of minerals in seawater. Free activity coefficients are those that are obtained in unassociated solutions and, in solutions in which specific ionic intcr-actions occur, are a construct that corre-sponds to the effects of the ionic strength alone. Total activity coefficients, on the other hand, are those mcasurcd in the pres-ence of specific interactions and are re-lated to free ones, when the ion-pairing model is used (Pytkowicz et al. 1966; Pyt-kowicz 1969)) by a=fp(F) =fg(T) (1) whcrc c1 is the activity, fill and fTl arc the fret and the total activity coefficients, and