Example General 3-Component Titration

The function Data EqAH2, m simulates the pH-titration of a weak diprotic acid, AH2, in acid excess, with a strong base. The computation of the equilibria is similar to the examples Eql. m and Eq2. m given in the Chapters Example General 3-Component Titration (p.56) and Example pH Titration of Acetic Acid (p.58). From the present point of view, the important aspect is that all variables are collected in one structure s. The model is now stored in s.Model, the logP values in s. log beta, etc. Importantly, all the information contained in s is returned to the invoking programs. 

The redox status of an aqueous system is described by the concentrations of the oxidized and reduced species of all system components. Redox systems, generally not at equilibrium as the result of kinetically slow redox reactions, are poorly characterized by intensity factors (Ej or pE) alone. Capacity factors, which reflect the total concentration of relevant species, are conservative parameters that can be meaningful guides to the redox status of aqueous systems. Oxidative capacity (OXC) is defined as a conservative quantity that incorporates a comprehensive chemical analysis of the redox couples of an aqueous system into a single descriptive parameter. OXC classifies aqueous systems in terms of well-defined geochemical and microbial parameters (e.g., oxic, sulfidic). Examples of model and actual groundwater systems are discussed to illustrate the concept. A redox titration model is another tool that is useful in describing a redox system as it approaches an equilibrium state. 

The identification of two (or more) components in a material by chemical methods alone can infer salt, co-crystal or solvate formation when one or both of the components is a liquid or a gas under ambient conditions. For example, when elemental or evolved gas analysis reveals that HCl or HBr, both gases under STP conditions, are present, salts are very likely to be formed, although rare cases of co-crystals have been reported. This was the case for a molecular HCl complex found for the mono-HCl salt of A - (15)-l-[2-(l- [(3S,4R)-l-/ert-butyl-4-(2,4-difluorophenyl)pyrrolidin-3-yl]carbonyl piperidin-4-yl)-5-chloro-phenyl]ethyl acetamide, wherein two equivalents of HCl were confirmed through elemental analysis, AgNOs titration and TG-MS.Remarkably, not one, but four crystal forms of this most unusual bis-HCl salt complex were identified, despite the presence of only one relatively basic site in the molecule. While HCl (or HBr) incorporation in a crystal usually signals salt formation and stoichiometric solvent retention generally points to solvate formation, the... 

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