Spectrophotometric determination of acidity constants of salicylaldoxime in aqueous solution at 25 degrees C and ionic strength of 0.5 M controlled with NaCl

The equilibrium constants of salicylaldoxime in water at 25 degrees C, 0.5 M of ionic strength with NaCl and concentration of 1x10(-4) M were determined spectrophotometrically. The spectral data were processed using SQUAD program. The salicylaldoxime in acid medium has the value of pKa1=1.224+/-0.027. In alkaline medium the salicylaldoxime has the values of pKa2=8.551+/-0.024 and pKa3=11.728+/-0.016.     

Formation constants at high ionic strength-II. The ionic strength correction of formation constants using a simplified pitzer equation

A simplified approach to the correction of equilibrium constants from one ionic strength and/or medium to another is developed. A computer program capable of performing these calculations is presented together with results of its application to the NH (3)H (+), CH (3)COO (-)H (+), CH (3)CH (2)COO (-)H (+), - OOCCH (2)COO (-)H (+) and HOOCCH (2)COO (-)H (+) systems.     

Effect of glycerol on micelle formation by ionic and nonionic surfactants at 25 degrees C

The effect of glycerol on the micellization of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and of the ethoxylated nonionic surfactant Brij 58 has been investigated by various experimental techniques. For both surfactants the critical micellar concentration (cmc), determined by surface tension measurements, is almost unaffected by the presence of glycerol in the mixture; only at high glycerol concentrations (>/=20% w/w) does the cmc significantly increase. The area per surfactant molecule at the air-solution interface, A, increases with increasing glycerol weight percentage, w(g). Fluorescence quenching measurements indicate that the presence of glycerol induces a lowering of the aggregation number of both surfactants. The glycerol intradiffusion coefficient has been measured by the pulsed-gradient spin-echo NMR technique as a function of glycerol content at constant surfactant concentration. It is almost unaffected by the presence of the surfactants, indicating that no direct glycerol-surfactant interaction occurs in the mixture. The surfactant intradiffusion coefficient has been also measured. In the case of CTAB, it increases with increasing glycerol concentration, a reflection of the decreased aggregation number. For Brij 58, in spite of the lowering of the aggregation number, the surfactant intradiffusion coefficient decreases with increasing glycerol concentration, suggesting an increase of the intermicellar interaction. The experimental evidence shows that for both surfactants the micellization is affected by the presence of glycerol through an indirect, solvent-mediated mechanism. In the case of CTAB, the main effect of glycerol is a lowering of the medium dielectric constant, which enhances the electrostatic interactions in solution. In the case of Brij 58, the results can be interpreted in terms of a salting-out effect according to which glycerol competes with the surfactant for water molecules, causing a dehydration of the surfactant ethoxylic headgroup.     

The acidic constants of 2-hydroxybenzohydroxamic acid in NaClO4 solutions at 25 degrees C

The protolysis equilibria of 2-hydroxybenzohydroxamic acid, H2SAX, have been studied at 25 degrees C in different ionic media by potentiometric titration with a glass electrode. The media were 0.513, 1.05, 2.21 and 3.5 mol/kg NaClO4. The constants beta(-p)(H2SAX<==>H(2-p)SAX(-p)+pH+), combined with salting effects of NaClO4 on H2SAX deduced from solubility determinations, were processed by the specific interaction theory, SIT, to give equilibrium constants at infinite dilution, log beta(-1)(o) = -7.655 +/- 0.013 and log beta(-2)(o) = -17.94 +/- 0.04, as well as specific interaction coefficients b(HSAX-,Na+) = 0.12 +/- 0.01 and b(SAX2-,Na+) = 0.17 +/- 0.02, molal(-1).     

Dependence of equilibrium constants ofL-valine on ionic strength according to Guggenheim,Scatchard and Pitzer models

Summary A systematic study of the dependence of acid-base stoichiometric constants on the ionic strength has been carried out for the aminoacidL-valine in ClK and BrK solutions. The observed dependence has been interpreted by using Guggenheim, Scatchard and Pitzer models for the activity coefficients of the species involved in the equilibria.

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Die Abhängigkeit von Gleichgewichtskonstanten desL-Valin von der Ionenstärke entsprechend den Modellen von Guggenheim, Scatchard und Pitzer

Zusammenfassung Es wurde anL-Valin in KCl- und KBr-Lösungen eine systematische Studie der Abhängigkeit der Säure-Base-Stöchiometrie von der Ionenstärke durchgeführt. Die beobachteten Abhängigkeiten wurden aufgrund der nach den Modellen von Guggenheim, Scatchard und Pitzer erhaltenen Aktivitätskoeffizienten der an den Gleichgewichten beteiligten Spezies interpretiert.

     

Formation constants beta(2) of calcium and magnesium fluorides at 25 degrees C

Until now, scientific work on the reactions of the complexation in water of fluoride ions with calcium or magnesium ions considered only soluble order 1 complexes (CaF(+) and MgF(+)). The precipitation of the compounds CaF(2) and MgF(2) did not take into account the preliminary formation in solution of these order 2 complexes (CaF(2)(0) and MgF(2)(0)). We therefore studied their formation using a direct potentiometric method in the F(-) ion-selective electrode at 25 degrees C. This experiment, together with a computerized thermodynamic study, allowed us to determine the values of formation constants at ionic strength equal to zero: log beta (CaF (2)(0))=5.7 and log beta (CaF (2)(0))=3.2 , as well as limiting solubilities: S(CaF(2))=10(-4.8) and S(MgF(2))=10(-5) mol l(-1). Then, some examples were studied showing the necessity to take into account the formation constant of CaF(2): the supersaturation of solutions, the validity of results from the fluoride selective electrode, the difference between released fluoride in distilled water and in artificial saliva in restorative dentistry, the fluoride concentration in hard waters and its health consequences.     

Solubility and first hidrolysis constants of europium at different ionic strength and 303 K

The solubility of europium at 0.02M, 0.1M and 0.7M NaClO₄ ionic strength solutions was determined by a radiometric method and pEu_s-pC_H diagrams were obtained. Hydrolysis constants were also determined at the same ionic strengths by pH titration and the values found were log *₁ = -7.68±0.11, -8.07±0.10 and -8.20±0.11. The log K _sp values were -23.5±0.2, -22.7±0.2 and -21.9±0.2 for 0.02M, 0.1M and 0.7M NaClO₄ ionic strengths, respectively, at 303 K under CO₂-free conditions and the extrapolated value at zero ionic strength was log K _sp ⁰ = -24.15. The working pC_H ranges for the calculation of the hydrolysis constants were selected from the pEu_s-pC_H diagrams in the region where precipitation of europium oxide or hydroxide was less than 20%. Europium removal from aqueous solutions with zeolites was explored.     

Potentiometric determination of the protonation constants of some phenols in 1.0 mol/L NaCl at 25°C

The potentiometric determination of the protonation constants of phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol and 2-methylphenol in 1.0 mol/L NaCl at 25°C is presented. An automated system has been used in the experiments. The determination of the constants has been carried out using both graphical and numerical methods.     

Acid-base equilibria in aqueous solution of cis-bis(trimethylphosphine)platinum(II) dinitrate at 25 degrees C, 0.2 M ionic strength. A potentiometric study

Acid-base equilibria in aqueous solutions of cis-bis(trimethylphosphine)platinum(II) dinitrate at 25 degrees C, 0.2 M ionic strength (KNO(3)), have been investigated by potentiometry with a glass electrode. The procedure consisted of multiple addition of the investigated analyte to a supporting electrolyte solution ("multiple sample addition") and subsequent titration with strong base. For the treatment of potentiometric multiple sample addition data, a new linearization procedure, suitable for an acid dissociation equilibrium whose product dimerizes, has been devised and tested. The potentiometric results have been interpreted with the support of NMR data. By dissociation of the first acidic function of the solute diaquo cation, cis-[(PMe(3))(2)Pt(OH(2))(2)](2+), a dimeric ampholite, cis-[(PMe(3))(2)Pt(mu-OH)](2)(2+), is quantitatively formed which, in turn, can be converted into the di-hydroxo derivative cis-(PMe(3))(2)Pt(OH)(2). The two acid dissociation steps involving two molecules of solute and condensation of ampholyte have pK(a1(c)) = 3.89 and pK(a2(c)) = 22.17.     

Dioxouranium(VI)-carboxylate complexes. Speciation of UO2(2+)-1,2,3-propanetricarboxylate system in NaCl(aq) at different ionic strengths and at t=25 degrees C

The formation constants of dioxouranium(VI)-1,2,3-propanetricarboxylate [tricarballylate (3-), TCA] complexes were determined in NaCl aqueous solutions at 0 < or = I/mol L(-1) < or = 1.0 and t=25 degrees C, by potentiometry, ISE-[H+] glass electrode. The speciation model obtained at each ionic strength includes the following species: ML-, MLH0, ML2(4-) and ML2H3- (M = UO2(2+) and L = TCA). The dependence on ionic strength of protonation constants of 1,2,3-propanetricarboxylate and of the metal-ligand complexes was modeled by the SIT (Specific ion Interaction Theory) approach and by the Pitzer equations. The formation constants at infinite dilution are [for the generic equilibrium p UO22+ + q (L3-) + r H+ = (UO2(2+))p(L)qHr(2p-3q+r); betapqr]: log beta110 = 6.222 +/- 0.030, log beta111 = 11.251 +/- 0.009, log beta121 = 7.75 +/- 0.02, log beta121 = 14.33 +/- 0.06. The sequestering ability of 1,2,3-propanetricarboxylate towards UO2(2+) was quantified by using a sigmoid Boltzman type equation.     

Potentiometric study of the protonation and distribution equilibria of 2-chlorophenol in NaCl medium at 25 degrees C. Construction of a thermodynamic model

The potentiometric determination of the protonation constant of 2-chlorophenol in NaCl media at different ionic strengths and its distribution coefficient between these media and two organic solvents at 25 degrees C are presented. An automated potentiometric system was used, and the determination of the constants was carried out using both graphical and numerical methods. A thermodynamic model using the modified Bromley methodology has been constructed for the prediction of protonation constants and distribution coefficients in NaCl media. The relevance of this study to the development of supported liquid membrane recovery systems is discussed.     

Effect of the medium on the ionization constants of some triazole compounds

The deprotonation and acid ionization constants of some triazole derivatives in various aqueous-organic solvent mixtures were determined potentiometrically at 20 degrees C. The organic solvents used were methanol, ethanol, DMF, DMSO, acetonitrile, acetone and dioxane. The high stabilization of both the non-protonated form by dispersion forces and of the proton by its interaction with the organic solvent are the main factors influencing the deprotonation constant in aqueous mixtures of methanol, ethanol, DMF or DMSO. On the other hand, the hydrogen bonding interactions and the solvent basicity, in addition to the electrostatic effect, contribute to the major effects in the deprotonation process (in solutions enriched with acetonitrile, acetone or dioxane) and the acid ionization process in different aqueous-organic solvent mixtures. Some thermodynamic parameters (delta H, delta G, delta S) of the ionization processes in a pure aqueous medium are also determined and discussed.     

Effect of temperature and ionic strength on volumetric and acoustic properties of solutions of urea alkyl derivatives in aqueous NaCl

The present work was undertaken to study volumetric and acoustic properties for diluted solutions of tetramethylurea in pure water and for urea, n-propylurea, n-butylurea and tetramethylurea in 0.5 or 1 mol · dm⁻³ aqueous solutions of sodium chloride. This paper presents measured values of densities and sound velocities at T = (288.15, 298.15 and 308.15) K. From these data the apparent molar volumes, V_Φ, adiabatic compressibilities, κ_S, and apparent molar adiabatic compressions, K_S,Φ, were obtained. The values of apparent molar volumes for infinite dilution and limited apparent adiabatic compressions were calculated from extrapolation of the concentration dependence. Further, the corresponding transfer data as well as hydration number of urea and its derivatives in the studied systems were estimated. The obtained parameters are discussed in terms of various solute-solvent and solute-cosolute interactions.     

The formal redox potential of the Ti(IV, III) couple at 25 degrees C in 1 M HCl 2 M NaCl medium

The formal redox potential of the Ti(IV, III) couple has been determined at 25 degrees C in 1 M HCl, 2 M NaCl aqueous medium, by emf measurements of a junction-free cell with glass and mercury electrodes. Ti(III) and Ti(IV) concentrations were changed by controlled electrolysis. The mean value of the searched formal potential, in a large range of total titanium concentration, is 9 +/- 1 mV against the molar hydrogen electrode in the same ionic medium.     

Formation constants at high ionic strength-I. Potentiometric determination of protonation constants for succinic, propionic and mono-methyl succinic acid in different ionic media

The protonation constants, K(r), for the ligands succinic acid (SA), mono-methyl succinate (MS) and propionate (PA) have been determined, at 25 degrees C, by glass electrode potentiometry in 3 mol/dm(3) (M) NaNO(3), KNO(3), NH(4)NO(3), Ca(NO(3))(2) and Et(4)NBr aqueous media. Results are compared with literature constants determined in 3M NaClO(4). The order of stability was found to be K(1)(SA) > K(1)(PA) > K(1)(MS) > K(2)(SA) and for the ligands in the different media K(r) followed the general trend with respect to the background electrolyte Et(4)NBr > NaClO(4) > KNO(3) > NaNO(3) > NH(4)NO(3) > Ca(NO(3))(2).     

The ionization of carbonic acid in Na-Mg-Cl solutions at 25°C

The stoichiometric pK₂ ^* and pK₂ ^* for the ionization of carbonic acid has been determined from emf measurements in NaCl solutions with small amounts of MgCl₂ from I=0.5 to 6.0 molal at 25°C. Our results at low ionic strengths (I=0.7) are in agreement with the measurements of Dyrssen and Hansson and Pytkowicz and Hawley. Our results have been analyzed using the ion pairing model and Pitzer's specific interaction equations. From the values of pK₁ ^*, we have determined the Pitzer parameters ⁰[Mg (HCO₃)₂] = 0.0193 and ¹[Mg (HCO₃)₂] = 0.0193 which reproduces the pK₁ ^* results to ±0.01. The values of pK₂ ^* were used to determine ⁰(MgCO₃) = 2.833, ¹(MgCO₃) = -15.069, ²(MgCO₃) = -204.90 and C (MgCO₃)=–0.970 which reproduces the pK₂ ^* s to ±0.02. The pK₂ ^* results could be reproduced to the same precision with fewer parameters using the ion pairing model [pK(MgCO₃)=3.00 and log (MgCO₃)=0.0560 I].     

Ionic strength dependence of formation constants-V Protonation constants of some nitrogen-containing ligands at different temperatures and ionic strengths

The protonation constants of 2,2'-bipyridyl, 1,10-phenanthroline, 1,3-diaminopropane, l-histidine and histamine have been determined potentiometrically, in the temperature range 10-40 degrees and at ionic strengths ranging from 0.04 to 1 (potassium chloride). The dependence of the protonation constants on ionic strength is described by a simple general equation. The enthalpy changes for the protonation of the ligands have been calculated from the temperature dependence of the protonation constants.     

The investigation of complex formation equilibria at constant ionic strength

The inert salts used for the investigations of complex formation are briefly discussed in relation to the effects of their ions on the equilibria studied. In general, some association with the inert salt ions cannot be completely avoided. In case of very stable complexes measured at low ionic strength, their effects can be quantified even though they are not caused by the anion if NO(-)(3) or ClO(-)(4) are used. In the case of weak complexes, when ionic strengths I > or =1 are used, the concentration of the complex of interest can be 1000 times lower than that of the associates of the same cation with the anion of the inert salt causing difficulties with the investigation of the latter systems. If the experimental results for K(1) of the alkaline-earth metal ions with fluoride in sodium perchlorate and sodium nitrate are correct, as their equilibrium constants have very similar values, it follows that the behavior of two anions is very similar. However, if NO(-)(3) associates with the above cations, as found, the same behavior is expected for ClO(-)(4). A more accurate analysis can only be done if activity coefficients in these solutions are known.     

Thermodynamics of concentrated electrolyte mixtures. I. Activity coefficients in aqueous NaCl−NaCl2 at 25°C

The activity coefficients of NaCl and CaCl₂ in NaCl?CaCl₂ aqueous mixtures have been measured at 25°C in the ionic strength range I=0.1–20. Where NaCl solubility permitted, both activity coefficients were measured over the whole range of compositions from pure NaCl to pure CaCl₂ at constant I. The measurements were made using Na and Ca ion-selective electrodes vs. a Cl ion-selective electrode. The data are fitted to Harned equations of the form $$log \gamma _A = log \gamma _A^0 - \alpha _{AB} y_B - \beta _{AB} y_B^2$$ and were also analyzed using the Pitzer formalism. Excess free energies of mixing are calculated and presented in the I=0.1–5.0 range and the Friedman parameters calculated.     

Effect of ionic strength and ionic interactions on the oxidation of Fe(II)

The rates of oxidation of Fe(II) in NaCl and NaClO ₄ solutions were studied as a function of pH (6 to 9), temperature (5 to 25°C), and ionic strength (0 to 6m). The rates are second order with respect to [H⁺] or [OH^–] and independent of ionic strength and temperature. The overall rate of the oxidation is given by