Carmelo Rigano

A non-linear least-squares approach to the refinement of all parameters involved in acid-base titrations.

A non-linear least-squares computer program has been written for the refinement of the parameters involved in potentiometric acid-base titrations. The program ACBA (ACid-BAse titrations) is applicable under quite general conditions to solutions containing one or more acids or bases. The method of refinement used gives the program several advantages over the other programs described previously.

The determination of formation constants of weak complexes by potentiometric measurements: experimental procedures and calculation methods

Experimental and calculation procedures for the study of weak complexes by the pH-measurement technique are described. An algorithm for the calculation of formation constants, together with a computer program in FORTRAN and BASIC versions, is reported. The problems of studying weak interactions are discussed. Simulated titration curves and experimental data for K(+)-thiodiacetate complexation were used to check the proposed method.

Ionic strength dependence of formation constants—I: Protonation constants of organic and inorganic acids

The protonation constants of formic, acetic, benzoic, oxalic, phthalic, maleic, malonic, succinic, dl-malic, dl-tartaric, aminoacetic, citric, nitrilotriacetic, ethylenediaminetetra-acetic, sulphuric and orthophosphoric acids have been determined from pH measurements, in tetraethylammonium iodide solution, at various ionic strengths in the range 0.01-1.0M (for phosphoric and sulphuric acids 0.01-0.5M). For each acid the dependence of the protonation constants on ionic strength was determined and an equation, valid for all the acids studied, to describe this was derived. The use of tetraethyl-ammonium salts as background to avoid ion-pair formation is discussed.

Computer analysis of equilibrium data in solution. ES5CM FORTRAN and BASIC programs for computing formation enthalpies from calorimetric measurements

Abstract A computer program was written in FORTRAN and BASIC languages for calculating enthalpy changes of complex formation in solution from direct calorimetric measurements. The program (ES5CM) can deal with any system in which mononuclear, polynuclear, protonated, hydroxo, mixed metal or mixed ligand complexes are formed. Particular attention has been paid to the robustness of the algorithm and to the possibility of using the program ES5CM with different machines, including small personal computers. Some test systems were used to check the efficiency of the program, and execution times for different machines are reported.

A computer method for the calculation of enthalpy changes for ion association in solution from calorimetric data

Abstract A general method for the determination of enthalpy changes in solution for systems containing an unlimited number of components, that can give rise to mononuclear, polynuclear, protonated, hydroxo and mixed species was set up. A computer program, DOEC, able to elaborate data on a calorimetric titration such as concentrations, changes to the mole number of the various species, solution ionic strength and reaction enthalpy was written. The program can also correct the ionic strength changes, that can occur during a titration. Thanks to the analogy of the mathematical expressions, the program can also be used for the treatment of spectrophotometric data.

On the possibility of determining the thermodynamic parameters for the formation of weak complexes using a simple model for the dependence on ionic strength of activity coefficients: Na+, K+, and Ca2+ complexes of low molecular weight ligands in aqueous solution

Alkali-metal and calcium(II) complexes of monocarboxylate A–(acetate and salicylate), dicarboxylate A2–(malonate, maleate, succinate, malate, tartrate, phthalate, and oxydiacetate), or amino acid HA (glycine or L-histidine) ligands have been studied potentiometrically, using a glasssaturated calomel electrode, at different temperatures and ionic strengths. The monocarboxylate ligands form [MA] and the dicarboxylates [MA] and [M(HA)] species (charges omitted) with both alkali metals and calcium. Glycine and L-histidine form [MA]+ and [M(HA)]2+{and [M(H2A)]3+ for L-histidine} complexes with Ca2+, whilst alkali metals form only [M(HA)]+ with glycine. Some interesting regularities in the formation constants are pointed out. From the dependence on temperature of formation constants, values of ΔH⊖ and ΔS⊖ have been determined. The function log β=f(I) has been carefully studied in the range 0.02 ⩽I⩽ 1 mol dm–3. The reliability of a new model for the dependence on ionic strength of formation constants (when dealing with weak complexes it is in practice impossible to use the constant ionic medium method) is widely discussed. Two methods of calculation are described and the more general method has been checked by simulated curves.

Ionic strength dependence of formation constants—XVIII. The hydrolysis of iron(III) in aqueous KNO3 solutions☆

The hydrolysis of iron(III) was studied potentiometrically at different ionic strengths in KNO(3) aqueous solutions, at 25 degrees C, to determine the dependence of hydrolysis constants on ionic strength (nitrate media), to check the existence of nitrate-ferric ion interactions, and to confirm the formation of high polymeric species. Under the experimental conditions 0.03 I (KNO(3)) 1M, 0.3 C 12 mM, the species Fe(OH)(2+), Fe(2)(OH)(4+)(2), Fe(OH)(+)(2) and Fe(12)(OH)(2+)(34) were found, and the hydrolysis constants log beta(11) = 2.20, log beta(12) = -2.91, log beta(22) = -5.7, log beta(12,34) = -48.9 (I = 0M) were calculated. The ionic strength dependence of hydrolysis constants is quite close to that found for several protonation and metal complex formation constants reported elsewhere.

Thermodynamic parameters for the protonation of carboxylic acids in aqueous tetraethylammonium iodide solutions

The protonation constants of 21 carboxylic acids (formic, acetic, propionic, benzoic, phenoxyacetic, salicylic, oxalic, malonic, succinic, itaconic, malic, tartaric, oxydiacetic, thiodiacetic, thiodipropionic, phthalic, maleic, citric, 1,2,3-tricarboxylic, 1,2,4-tricarboxylic and 1,2,4,5-tetracarboxylic), have been determined potentiometrically, by pH-metric measurements, at several temperatures and ionic strengths, 5≤T≤55°C, 0<1≤1 mol-dm−3, using tetraethylammonium iodide as background salt. General equations for the dependence on ionic strength of thermodynamic parameters have been found. The statistical significance of results and the possibility of using a simple model for the thermodynamics of carboxylic acids protonation, is discussed.

The calculation of equilibrium concentrations in large multimetal/multiligand systems

Abstract An algorithm for computing equilibrium concentrations by the “equilibrium constant” method is described. The main features of this algorithm are: (a) a damping procedure in conjunction with the Newton-Raphson technique that avoids divergence in dealing with very complicated (simultaneous presence of simple, mixed, protonated, polynuclear and hydroxypolynuclear species) and/or very large systems; (2) the use of devices to decrease core requirements, calculation time, and ill-conditioned problems; and (3) the calculation of errors in free and species concentrations from the uncertainties in analytical concentrations and in formation constants. Four systems are used for testing computer programs on calculation of equilibrium concentrations.

Ion association of Cl− with Na+, K+, Mg2+ and Ca2+ in aqueous solution at 10 ⩽ T ⩽ 45 ° C and 0 ⩽ I ⩽ 1 mol l−1: A literature data analysis

Abstract The formation constants of [Na(Cl)] 0 , [K(Cl)] 0 , [Mg(Cl)] + and [(CaCl)] + ion pairs have been calculated by using literature data obtained from different techniques at different temperatures and ionic strengths. Results are reported together with estimated errors, and their reliability is discussed. Formation enthalpies and entropies are calculated from the dependence on temperature of formation constants. A computer program for the calculation of dependence on temperature and ionic strength of thermodynamic parameters is described.