Silvio Sammartano

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.

Thermodynamic study on the formation of the cupric ion hydrolytic species

Abstract The formation constants of Cu(OH), Cu2(OH)2 and Cu3(OH)4 were determined by potentiometric measurements. The enthalpy changes were obtained by direct calorimetry. The species were individualized by statistic tests. The calculated entropy changes were correlated with the assumed structure of the species present in the solution.

A new approach in the use of SIT in determining the dependence on ionic strength of activity coefficients. Application to some chloride salts of interest in the speciation of natural fluids

Abstract This paper describes a modified version of the SIT (Specific ion Interaction Theory) method and its use in determining the dependence on ionic strength of activity coefficients. In the new approach the interaction coefficients (ε) are not constant but depend on ionic strength (I /mol kg-1) according to the simple relationship: ε = ε∞+ (ε0 - ε∞) / (l + 1) where ε0 and are true constants for I→ 0 and l→ ∞, respectively. To check the two parameter SIT equation, we calculated ε0 and for the activity coefficients of HCl, LiCl, NaCl, KCl, MgCl2, CaCl2 and SrCl2, in a wide ionic strength range (0.1 ≤ l/mol kg-1 ≤ 4.5, for KCl; 0.1 ≤ l/mol kg-1 ≤ 6, for HCl, LiCl, NaCl; 0.3 ≤ l/mol kg-1 ≤ 12, for SrCl2; 0.3 ≤ l/mol kg-1 ≤ 15, for MgCl2; 0.3 ≤ l/mol kg-1 ≤ 18, for CaCl2). Results show that the γ values calculated using this approach fit quite well over the whole I-range for all the electrolytes considered. Comparison is made with the analogous one parameter SIT equation. The temperature coefficients of interaction coefficients were also calculated using (HCl) in the range 0 ≤ t/°C ≤ 60.

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.

Protonation of carbonate in aqueous tetraalkylammonium salts at 25 °C

Protonation constants of carbonate were determined in tetramethylammonium chloride (Me(4)NCl(aq) 0.1</=I/molkg(-1)</=4) and tetraethylammonium iodide (Et(4)NI(aq) 0.1</=I/molkg(-1)</=1) by potentiometric ([H(+)]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaCl(aq) (0.1</=I/molkg(-1)</=6) were also critically analysed. Both protonation constants of carbonate follow the trend Et(4)NI>Me(4)NCl>NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated.

Solubility and Activity Coefficients of Acidic and Basic Nonelectrolytes in Aqueous Salt Solutions. 2. Solubility and Activity Coefficients of Suberic, Azelaic, and Sebacic Acids in NaCl(aq), (CH~3)~4NCl(aq), and (C~2H~5)~4NI(aq) at Different Ionic Strengths and at t = 25 ^oC

The solubility of three dicarboxylic acids, (COOH)-(CH 2 ) n -(COOH) (n = 6, 7, 8), was determined in NaCl(aq) (0.5 to 4.5) mol·L -1 , (CH 3 ) 4 NCl(aq) (0.25 to 3) mol·L -1 , (C 2 H 5 ) 4 NI (0.25 to 1) mol·L -1 , and in pure water at t = 25 °C. The solubility trend is (C 2 H 5 ) 4 NI > (CH 3 ) 4 NCl > NaCl. The Setschenow constants and activity coefficients of neutral species were calculated from these data. To fully characterize the acid-base behavior of above dicarboxylic acids, the protonation constants were determined in the same conditions. From these data, together with solubility ones, Pitzer and SIT parameters were calculated.

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.