Thermodynamics of electrolyte solutions. The system HCl + CaCl2 + H2O at 298.15°K

Activity coefficients of hydrochloric acid have been determined from electromotive-force measurements of cells containing mixtures of hydrochloric acid and calcium chloride at constant total ionic strengthsI=0.1, 0.5, 1.0, 2.0, and 3.0 mole-kg^–1 at 298.15°K. Interpretations based on Scatchard's and Pitzer's equations indicate that Pitzer's equations probably provide a more convenient guide to the thermodynamic properties of the mixed-electrolyte solutions. Activity coefficients for calcium chloride were derived from these equations.     

Activity coefficients in aqueous mixtures of hydrochloric acid and lanthanum chloride at 25°C

Activity coefficients of hydrochloric acid in aqueous solutions of lanthanum chloride were determined by an emf method at 25°C over an ionic strength range 0.05–3 mol-kg^–1. Harned's rule was obeyed within experimental error by the acid in all the mixtures. However, the fit with Pitzer's equations was not as good as the Harned rule fit, even though the effects of higher-order electrostatic terms were considered. Activity coefficients for the salt in the mixtures were derived using the Pitzer equations and fitted to the Harned equation, whereupon Harned's rule was found to be valid for the salt up to an ionic strength of 0.3 mol-kg^–1 only.     

Electromotive-force studies of mixed electrolytes in mixed solvents. HCl+NH4Cl in methanol+water solvents at 25°C

Electromotive-force measurements of the cell Pt, H₂(g, 1 atm)|HCl(m₁), NH₄Cl(m₂), methanol(X%), Water(100–X)%|AgCl|Ag have been made at 25°C for m₁+m₂=1 mole-kg^–1 and X=0, 10, 20, 30, 40, and 50% methanol by weight. Hydrochloric acid obeys Harned's rule in aqueous solutions, but a quadratic term is required in the mixed solvents. The Harned coefficients for the acid vary with solvent composition, and this invalidates the applicability of Harned's method for estimating activity coefficients for single electrolytes in mixed solvents. This method is described and the reason for the inapplicability of the method is discussed in terms of ion-ion and ion-solvent interactions.     

Activity and osmotic coefficients oft-butylammonium chloride; Activity coefficients of HCl in mixtures with tris hydrochloride ort-butylammonium chloride at 25°C

In an earlier study, the activity coefficients of aqueous mixtures of HCl with the hydrochlorides of tris(hydroxymethyl)aminomethane (Tris) ort-butylamine (t-B) were determined at ionic strengths of 0.1, 0.5, and 1.0 mol-kg^–1. The work has been extended to ionic strengths of 2.0 and 3.0 through emf measurements with hydrogen and AgCl/Ag electrodes at 25°C. The results are considered in terms of Harned's rule and the Pitzer and Rush-Johnson-Scatchard treatments of activity coefficients in electrolyte mixtures. In order to compare ionic interaction parameters in the two systems, the activity coefficients and osmotic coefficients of t-butylammonium chloride at molalities up to saturation (7.14 mol-kg^–1) were determined by the gravimetric isopiestic method with solutions of NaCl as reference. The behavior for both systems can be accounted for satisfactorily in terms of binary (H⁺–N⁺) and ternary (H⁺–N⁺–Cl^–) interactions, where N⁺ is either Tris·H⁺ or t-B·H⁺.     

Activity coefficients for ternary systems: VI. The system HCl + MgCl2 + H2O at different temperatures; application of Pitzer's equations

Electromotive-force measurements have been made on HCl–MgCl₂–H₂O mixtures at 5, 15, 25, 35 and 45°C at eleven different ionic strengths from 0.1–5.0 mol-kg ^–1 . The results are interpreted in terms of the simple Harned's equations, as well as the more complicated Pitzer ion-component treatment of multicomponent electrolyte mixtures. Activity coefficients for HCl in the salt mixtures obey Harned's rule up to and including I=5.0. For the salt in the acid mixtures, Harned's rule holds true up to and including I=0.5. The contribution of higher-order electrostatic terms (E and E') in the Pitzer equations is important for accurate evaluations of unlike cation-cation interactions (_H,Mg), and cation-anion-cation interactions (_H,Mg,Cl). The values of^S_H,Mg and _H,Mg,Cl (determined with E and E'), _H,Mg and _H,Mg,Cl (determined without E and E'), as well as the trace activity coefficients of HCl, _tr ^A , in solutions of MgCl₂ (where ionic strength fraction of the salt,y _B = 1) at all the experimental temperatures and ionic strengths, are reported. Results of this study are compared with those for similar systems. At I=0.1 and 25°C, the results of the Brönsted-Guggenheim specific interaction theory are discussed briefly.     

Activity coefficient of hydrochloric acid in HCl/MgCl2 mixtures and HCl/NaCl/MgCl2 mixtures from 5 to 45°C

Magnesium, the dominant bivalent cation in natural seawater, exerts a substantial influence on the patterns of ion interactions in this saline medium. Mean activity coefficients of hydrochloric acid in mixtures of this acid with magnesium chloride at four ionic strengths, namelyI=0.1, 0.3809, 0.6729, and 0.8720 mole-kg^–1, were obtained from emf measurements of cells without liquid junction at nine temperatures from 5 to 45°C. The three highest ionic strengths correspond to seawater of salinities 20, 35, and 45, respectively. In addition, mixtures of HCl, NaCl, and MgCl₂ were studied atI=0.6729, the molal ratio of NaCl to MgCl₂ being maintained at 7.202 as in natural seawater. The Harned coefficients _{1 2} were found to decrease slowly with increase in temperature. The trace activity coefficient of HCl in solutions of MgCl₂ as well as in NaCl MgCl₂ mixtures was found to be nearly identical with that measured earlier in synthetic seawater of the same ionic strength but containing NaCl, MgCl₂, KCl, and CaCl₂.     

Thermodynamics of Electrolyte Mixtures: HCl + NdCl<Subscript>3</Subscript> + H<Subscript>2</Subscript>O from 5 to 55 <Superscript>∘</Superscript>C

Electromotive-force (emf) measurements of cells containing solutions of hydrochloric acid and neodymium chloride were reported at constant total ionic strengths (I) of 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, and 1.5 mol-kg⁻¹ at 11 temperatures ranging from 5 to 55 ^∘C, and at I = 2.0 mol-kg⁻¹ at 25 ^∘C. Hydrogen and silver–silver chloride electrodes were used in these cells. Results from the emf measurements, the mean molal activity coefficients of HCl in HCl + NdCl₃ + H₂O mixtures, as well as the Harned interaction coefficients using Harned's rule are reported in the preceding article in this issue. The ion-interaction model of Pitzer is applied here for the evaluation of the Pitzer mixing coefficients, ^Sθ_H,Nd and ψ_H,Cl,Nd, as well as the linear representation of the temperature derivatives of ∂^Sθ_H,Nd /∂ T and ∂ψ_H,Nd,Cl/∂T. The activity coefficients at several ionic strength fractions y of NdCl₃ are given at 25 ^∘C. The results are interpreted in terms of ionic interactions.     

Activity coefficients for HCl+NiCl2+H2O at 298.15°K and effects of higher-order electrostatic terms

Activity coefficients for CHl in the system HCl+NiCl ₂ +H ₂ O at 298.15°K at constant total ionic strengths of 0.1, 0.5, 1.0, 2.0, and 3.0 moles-kg ^–1 have been determined by an emf method. A comparison was made between Scatchard's and Pitzer's interpretations of mixed-electrolyte solutions for this system and six related systems. Preference can be given to Pitzer's method provided cognizance is taken of the effects of higher-order electrostatic terms beyond the Debye-Hückel approximation on the thermodynamic properties of asymmetrical mixtures.     

Ionic interactions in the system HBr + BaBr2 + H2O at 25°C

Electromotive-force measurements are reported for mixtures of HBr and BaBr₂ in water at 25°C at constant total ionic strengths. Activity coefficients for HBr were analyzed using Pitzer's equations and Scatchard's neutral-electrolyte treatment. Both methods gave comparable results if the effects of higher-order electrostatic terms on the H⁺–Ba⁺² interactions were included in Pitzer's treatment. Furthermore, the value of the H⁺–Ba⁺² interaction parameter, (s), which should be independent of the anion, is indeed close to that for binary mixtures of these ions having chloride as common ion.     

Activity coefficients in binary electrolyte mixtures HCl + MgCl2 + H2O at 298.15°K

Activity coefficients of hydrochloric acid in aqueous mixed solutions with magnesium chloride have been determined at 298.15°K from electromotiveforce measurements of the cell Pt, H₂(g, 1 atm.)HCl(m_A), MgCl₂(m_B)AgClAg at constant total ionic strengths of 0.1, 0.5, 1.0, 2.0, and 3.0 moles-kg^–1. The data were interpreted in terms of Scatchard's and Pitzer's equations whereupon it was found that the former gave a better fit of the experimental data but the latter were reasonably adequate. Activity coefficients for magnesium chloride in the mixtures were derived using Pitzer's equations.     

Activity Coefficients for the System HCl +GaCl3 + H2O from 5 to 55°C

Activity coefficients for HCl in HCl + GaCl₃ + H₂O at eleven different temperatures from 5 to 55°C have been determined at total experimental ionic strengths from 0.01 to 3.0 mol-kg^–1 using a cell of the type: Pt; H₂(g, 1 atm)|HCl (m_A) + GaCl₃(m_B)|AgCl, Ag (A) The results for the 770 experimental emf data points have been used to determine the variation of the activity coefficients of HCl with the change in molality of GaCl₃ in the solution. It is found that the linear form of Harned's rule is not obeyed for this system.     

Activity coefficient of hydrochloric acid in the system HCl−KCl−H2O at 25°C and lonic strengths from 0.1 to 3 moles-kg−1

The activity coefficient of hydrochloric acid has been determined in HCl–KCl–H₂O mixtures at 25°C and for seven values of the ionic strength between 0.1 and 3.0 mole-kg^–1, using the cellPt;H ₂(g, 1atm)\HCl(m _A ),KCl _B AgCl;Ag The results are compared with those of previous studies of the same system and are interpreted in terms of ionic interactions specific to the mixture by use of Pitzer's treatment of mixed electrolyte solutions.     

Thermodynamics of mixed electrolyte solutions. IX. Calculation of the osmotic and activity coefficients in a pseudoternary system (NaCl−nKCl)−MgCl2-H2O at 298.15°K

The equation of Reilly, Wood, and Robinson was used to predict the osmotic coefficient of a pseudoternary system (NaCl–nKCl)–MgCl₂–H₂O over a molal ionic strength range of 1.0 to 5.0 moles-kg^–1. The results are in close agreement with experimental data at most ionic strengths. The standard deviation in the osmotic coefficients over the entire concentration range lies within 0.0035. The predicted values of the mean activity coefficients are in good agreement with those obtained by the treatments of both Scatchard and Friedman. Mean activity coefficients for the other components were also predicted.     

The system HCl+InCl3+H2O from 5 to 55°C: Application of Harned's rule

Electromotive-force measurements of cells containing hydrochloric acid and indium chloride have been made to determine the variation of the log of the activity coefficient of hydrochloric acid with change in the amount of indium chloride in the solution. The simpler Harned equations have been used to fit the data. The quadratic terms in the Harned equations for the activity coefficients of HCl in the salt mixtures are required for a good fit of the 968 experimental emf data points at all the experimental ionic strengths and temperatures. The more convenient Pitzer ion-interaction treatment of the data will be reported in a separate publication which will include the values of the Pitzer parameters for pure InCl₃(aq), and mixing parameters for H⁺–In⁺³ and H⁺–In⁺³–Cl^–. A comprehensive investigation on the mixed electrolyte solutions at 11 different constant total ionic strengths ranging from 0.05 to 3.5 mol-kg^–1 was made at 11 temperatures from 5 to 55°C using the cell without liquid junction of the type: Pt,H₂(g, 1 atm)|HCl(m _A)+InCl₃(m _B)+H₂O|AgCl,AG (A).     

The System HCl + NdCl3 + H2O from 5 to 55 ∘C: A Study of Harned's Rule

The activity coefficients of HCl (γ_A) in aqueous mixtures of HCl and NdCl₃ were determined by the electromotive-force (emf) measurement of cells without liquid junctions of the type:

Thermodynamic Study of the NaCl + Na2SO4 + H2O System by Emf Measurements at Four Temperatures

Activity coefficients for sodium chloride in the NaCl + Na₂SO₄ + H₂O ternary system were determined from emf measurements of the cell

Thermodynamics of the In|In+3 Electrode in HCl + InCl3 Solutions

Electromotive force measurements have been made using the cell $$\mbox{In(s)}|\mbox{HCl }(m_{\mathrm{A}}),\mbox{InCl}_{3}(m_{\mathrm{B}}),\mbox{H}_{2}\mbox{O}|\mbox{AgCl, Ag}$$ in the ionic strength range of I=0.05, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol?kg^?1 at 25?°C. The value of E ^o, the standard potential of the In/In³⁺ electrode, has been determined at 25?°C. Our value of E ^o (?0.3371 V) at 25?°C obtained from our measurements is in good agreement with ?0.336 (Hakomori, J. Am. Chem. Soc. 52: 2372–2376, 1930) and ?0.3382 V (Covington et al., J. Chem. Soc. 4394–4401, 1963). The activity coefficients of InCl₃ as well as Harned interaction coefficients have been determined at 25?°C for each of the experimental ionic strengths at ionic strength fractions of 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 of HCl. Harned’s rule for the salt is obeyed at I=0.05,0.1 and 0.25 mol?kg^?1 but the quadratic terms are needed for higher ionic strengths. These data, together with others for the activity coefficient of HCl in the same solutions, have been treated by the ion-interaction (Pitzer, Activity Coefficients in Electrolyte Solutions, CRC Press, 1991) equations in a previous publication.     

Specific ionic interactions in the quaternary systems HCl−NaCl−KCl-water and HCl−NH4Cl−KCl-water at 25°C

Mean ionic activity coefficients of hydrochloric acid in the systems HCl–NaCl–KCl-water and HCl–NH₄Cl–KCl-water at constant total ionic strength of 1 mole-kg^–1 have been determined for various ratios of the added salts at 25°C. The electromotive force method was used. Both an extended form of the simple empirical Harned equations (see ref. 1) and the more complicated semiempirical Pitzer equations (see refs. 2–4) for multicomponent electrolyte systems were used in the treatment of the data. Specific ionic interaction parameters for both types of equations are reported. The effects of the added salts on the thermodynamic behavior of HCl in the two systems mentioned were compared by considering the variation of its trace activity coefficient with change in amounts of the added salts at constant total ionic strength of 1 mole-kg^–1.     

Kinetics of anation of hexaaquachromium(III) by thiocyanates – specific salt effects

The kinetics of anation of hexaaquachromium(III) by thiocyanates follows the rate law: –d[complex]/dt=k[NCS] (20–40°C, [NCS^–]=0.1–0.6M, I=2.0M, pH=1.0). The specific salt effect has been studied for five media: NaCl, NaBr, NaClO₄, KCl and CsCl. The series of chloride (Na⁺, K⁺ and Cs⁺) salts show a negligible effect on the anation rate. On the contrary, the series of sodium salts (Cl^–, Br^– and ClO ₄ ^– ) reveal a marked difference in the reaction rate. The anation rate decreases sharply with the ionic strength increase (I=0.2–2.0M, NaCl). The results were interpreted within the frame of fast equilibria of ion-pair formation followed by an interchange mechanism step. The difference of reaction rate is a result of competition between anions (thiocyanates and supporting electrolyte anions) to the complex cation at an ion-pair formation process.     

Ionic strength dependence of formation constants. Part 4. Potentiometric study of the system Cu2+-Ni2+-citrate

Summary The ternary Cu²⁺-Ni²⁺-citrate (cit^3–) system was investigated potentiometrically in aqueous solution, at different temperatures, 10t45°C, and ionic strengths, 0.03I0.8 mol dm^–3, using potassium nitrate or tetraethylammonium bromide as background salt. Since the citrate anion forms weak complexes with potassium, the stability constants here reported differ according to whether the potassium association is considered or not. In the presence of both Cu²⁺ and Ni²⁺, the mixed metal species, [CuNi(cit)₂H_–2]^4– is formed with citrate in solution, in addition to the various binary complexes. We have obtained the dependence for all the formation constants on ionic strength and temperature. The previous suggestions concerning a general equation for describing the dependence, log =f(I), are confirmed; from the study of log =f(T) we have obtained the values of thermodynamic parameters. The dependence of H on ionic strength is discussed.