Chapter 12
Modelling of Natural Fluids: Are the Available
Databases Adequate for this Purpose?
D. Ferri . C. Manfredi . E. Vasca . C. Fontanella . V. Caruso
12.1
Introduction
The research activity in our laboratory does not directly focus on marine chemistry.
However it is mainly devoted to the study of equilibrium reactions that take place in
natural systems, of which the sea is certainly one of the most important, and to determination of their behaviour.
Let us start by stating that the guidelines adopted in our laboratory are those developed by L. G. Sillen and his school in Stockholm. The primary rule we abide to is to
pay greatest attention to experimental adequacy and accuracy, as we are convinced
that bad data cannot be improved by any computerized treatment, powerful as it may
be. The interpretation of good data can often be improved. Bad data remain bad. An
obvious consequence of this creed of ours is a constant effort to optimize the experimental methods. To this crucial point we will return later.
Chemists are generally familiar with the terminology, the fields of pertinence, the
investigation, and the interpretation methods adopted in Equilibrium Analysis (EA).
But what is, in fact, equilibrium analysis? In answering this question, let us confine
our interest to aqueous solutions. In water, chemical interactions mainly take place
through acid-base, redox, precipitation or complexation reactions. The products may
be species capable of individual existence. If so, they can be characterized by means
of the classical analytical methods, which generally imply one or more separation steps
prior to the analysis. Alternatively, the products formed may be complexes, i.e. species
in a dynamic, often reversible chemical equilibrium, which obey the law of mass action and thus cannot be separated. In this case, they are characterized by measuring
one or more physico-chemical properties of the solution (electrode potential, absorbance of electromagnetic radiation, solubility of solid phases, distribution between
solvents, etc.) without perturbing the state of equilibriuml. It is obvious that to identify and to quantify the products of a reaction requires a totally different approach in
the two cases. The experimental techniques and the methods of interpretation of the
data developed for the study of chemical equilibria in aqueous solutions, particularly
by Scandinavian chemists, constitute the basis of the equilibrium analysis.
To investigate a chemical equilibrium implies the determination of the composition of the species (complexes) formed by the reaction of one or more co-ordinating
reagents with one or more ligands, as well as their formation constants. This is the
1 For the sake of completeness, the kinetic methods, based on the study of the relaxation, following
the perturbation of the state of equilibrium, must also be mentioned.
Modelling of Natural Fluids: Are the Available
Databases Adequate for this Purpose?
D. Ferri . C. Manfredi . E. Vasca . C. Fontanella . V. Caruso
12.1
Introduction
The research activity in our laboratory does not directly focus on marine chemistry.
However it is mainly devoted to the study of equilibrium reactions that take place in
natural systems, of which the sea is certainly one of the most important, and to determination of their behaviour.
Let us start by stating that the guidelines adopted in our laboratory are those developed by L. G. Sillen and his school in Stockholm. The primary rule we abide to is to
pay greatest attention to experimental adequacy and accuracy, as we are convinced
that bad data cannot be improved by any computerized treatment, powerful as it may
be. The interpretation of good data can often be improved. Bad data remain bad. An
obvious consequence of this creed of ours is a constant effort to optimize the experimental methods. To this crucial point we will return later.
Chemists are generally familiar with the terminology, the fields of pertinence, the
investigation, and the interpretation methods adopted in Equilibrium Analysis (EA).
But what is, in fact, equilibrium analysis? In answering this question, let us confine
our interest to aqueous solutions. In water, chemical interactions mainly take place
through acid-base, redox, precipitation or complexation reactions. The products may
be species capable of individual existence. If so, they can be characterized by means
of the classical analytical methods, which generally imply one or more separation steps
prior to the analysis. Alternatively, the products formed may be complexes, i.e. species
in a dynamic, often reversible chemical equilibrium, which obey the law of mass action and thus cannot be separated. In this case, they are characterized by measuring
one or more physico-chemical properties of the solution (electrode potential, absorbance of electromagnetic radiation, solubility of solid phases, distribution between
solvents, etc.) without perturbing the state of equilibriuml. It is obvious that to identify and to quantify the products of a reaction requires a totally different approach in
the two cases. The experimental techniques and the methods of interpretation of the
data developed for the study of chemical equilibria in aqueous solutions, particularly
by Scandinavian chemists, constitute the basis of the equilibrium analysis.
To investigate a chemical equilibrium implies the determination of the composition of the species (complexes) formed by the reaction of one or more co-ordinating
reagents with one or more ligands, as well as their formation constants. This is the
1 For the sake of completeness, the kinetic methods, based on the study of the relaxation, following
the perturbation of the state of equilibrium, must also be mentioned.