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A quantitative approach to the inorganic carbon system in aqueous media used in biological research: dilute solutions isolated from the atmosphere
Author(s) -
HELDER R. J.
Publication year - 1988
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1988.tb01140.x
Subject(s) - alkalinity , ionic strength , chemistry , activity coefficient , thermodynamics , dilution , ionic bonding , dissociation (chemistry) , carbonate , aqueous solution , equilibrium constant , ion , inorganic chemistry , physics , organic chemistry
Abstract. The changes in the distribution of dissolved inorganic carbon systems resulting from biological activity are described using the dissociation equations and considering eight variables: the concentrations or activities of H + , OH − , CO 2 , H 2 CO 3 , HCO 3 − , CO 3 2− , total carbon ∑CO 2 , carbonate alkalinity A − and base excess B + . Equations for the equilibrium constants K 1 , K 2 and K 3 , giving their dependence on temperature, are provided. These thermodynamic constants are defined on the infinite dilution scale and their dependence on the pH‐convention adopted is stressed. From the dissociation equations and the eleclroneutrality condition a set of 15 equations were deduced, each representing the relationship between the H + ‐activity and one pair of the other variables. The knowledge of two variables will, therefore, enable the calculation of all the other variables, furnishing a complete description of the C‐system. Such a description is needed to permit the calculation of the ionic strength (I) of a solution. Knowing I makes it possible to calculate the activity‐coefficients for bicarbonate and carbonate ions (Debye‐Hueckel equations), which are needed to calculate the working constants K 1 and K 2 from the thermodynamic ones. Hints for computer programs, some of them including iterative subroutines, are given. Suggestions are made for the experimental determination of K 1 and K 2 . The discussions arc restricted to dilute solutions isolated from a gaseous phase, at 1 atm, external pressure and having an ionic strength of not more than 70 mol m −3 . The difficulty of providing causal explanations in studies involving the C‐system is briefly discussed.