Ultrasonic vibration potentials,apparent molal volumes,and apparent molal heat capacities of 1:1 electrolytes in acetonitrile

The ultrasonic vibration potentials and apparent molal volumes for many inorganic and organic electrolytes were measured in acetonitrile at 25°C and combined to obtain ionic contributions to the standard partial molal volumes V°(ion). Monatomic cations and anions of the same size essentially have the same V°(ion). Their size dependence can be interpreted through Hepler's equation. The apparent molal heat capacities were also measured in acetonitrile and used to derive standard values. Various methods of estimating C _p ⁰ (ion) were investigated and an ionic scale is proposed. It is concluded that C _p ⁰ (ion) of large organic ions are very close to the intrinsic heat capacities of the ions, and the solvation contribution to monatomic ions is positive for both cations and anions.     

Partial molal volumes of ions in organic solvents from ultrasonic vibration potential and density measurements. III. Dimethylsulfoxide

The partial molal volumes of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Cl^–, Br^–, I^–, and NO ₃ ^- in DMSO at 25°C have been determined from ultrasonic vibration potential data and density data for solutions of uni-univalent electrolytes. Hepler's semiemprirical equation has been used to split ionic partial molal volumes into geometric and electrostrictive contributions. The results obtained in this work confirm the conclusion of our previous studies, namely, that the contribution of electrostriction is essentially determined by the properties of that layer of atoms, 0.3 to 0.4 nm thick, in contact with the ion and by the degree of steric hindrance of the poles of the dipole of the solvent molecule. On the other hand, the geometric contribution depends on the size of the solvent molecule and also on the arrangement of the solvent molecules about the ions. It is shown that the geometric contribution to the partial molal volume of ions is largely increased when ions cannot come close enough to the poles of the solvent-molecule dipole, owing to steric hindrance.     

Group additivity for partial molal heat capacities and volumes of alkanes in methanol at 25°C

A flow heat capacity calorimeter and a flow vibrating tube densimeter have been used to measure the apparent molal heat capacities and volumes of 14 linear and branched alkanes in methanol at 25°C. These quantities have been extrapolated to infinite dilution to obtain the standard partial molal heat capacities and volumes. The C _p2 ^o and V ₂ ^o data can be expressed by equations having the general form: Y=A_Y+ N_k Y_k+(steric factors), where A_Y is solute independent and the Y_k terms are the individual group contributions. A rationale for use of the above equation is presented.     

The effect of pressure on the ionization of water at various temperatures from molal-volume data1

The apparent molal volumes of dilute (0.002 to 1.0m) aqueous HCl and NaOH solutions have been determined at 0, 25, and 50°C and NaCl solutions at 50°C. The partial molal volumes ( ) of HCl, NaOH, and NaCl solutions have been determined from these apparent molal volumes and other reliable data from the literature. The partial-molal-volume changes ( ) for the ionization of water, H₂OH⁺+OH^–, have been determined from 0 to 50°C and 0 to 1m ionic strength from the partial molal volumes of HCl, NaOH, NaCl, and H₂O. The partial molal compressibilities ( for HCl, NaOH, NaCl, and H₂O have been estimated from data in the literature and used to determine the partial molal compressibility changes ( ) for the ionization of water from 0 to 50°C and 0 to 1m ionic strength. The effect of pressure on the ionization constant of water has been estimated from partial-molal-volume and compressibility changes using the relation from 0 to 50°C and 0 to 2000 bars. The results agree very well with the directly measured values.Contribution Number 1548 from the University of Miami.     

Group additivity for the standard partial molal heat capacities and volumes of polar compounds in methanol at 25°C

A flow heat capcity calorimeter and a flow vibrating tube densimeter have been used to measure the apparent molal heat capacities and volumes of benzene and 25 polar compounds in methanol at 25°C. These quantities have been extrapolated to infinite dilution to obtain the standard partial molal heat capacities and volumes. The and data have been used in conjunction with an additivity scheme previously determined for alkanes. Group contributions were evaluatd for –OH, –NH₂, –COOH, –C₆H₅, C=O, –COO–, –CONH–, –O–, –S–, and –S₂–. The concentration dependences of _cp and _v of nonelectrolytes in methanol are qualitatively similar but much smaller than in water.     

Solution thermodynamics of first row transition elements. 3. Apparent molal volumes of aqueous ZnCl2 and Zn(CIO4)2 from 15 to 55°C and an examination of solute-solute and solute-solvent interactions

The apparent molal volumes of aqueous ZnCl₂ and Zn(ClO₄)₂ solutions have been measured from 15–55°C. The dilute solution data are extrapolated to infinite dilution using the Redlich-Meyer equation. The full concentration range data are fitted with the Pitzer formalism. The data are then compared with the data on the previously measured salts of Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, and Cu²⁺. The effect of complex ion formation is easily seen in the Cu²⁺ and Zn²⁺ salt data. A new approach to single ion volumes from salt volumes is proposed. The calculated ionic volumes at infinite dilution are compared, and it is clear that crystal field effects must be considered in any quantitative theory of transition element volumes.     

Partial molal volumes of alcohols in propylene carbonate at 25°C

The densities of the homologous series of alcohols and diols R_nCH₂OH (n=2–6), CH₃CHOHR_n (n=1–5), 1,2-propanediol, 1,3-1,4-, and 2,3-butanediol, 1,5-pentanediol, and 1,7-heptanediol dissolved in propylene carbonate have been measured at 25°C. The partial molal volumes at infinite dilution have been evaluated. Additivity of group molal volumes has been confirmed in propylene carbonate. The results have been discussed in relation to the same data in aqueous solution, and the scaled particle theory has been employed to calculate intrinsic volumes of the solutes.     

Partial molal volumes and adiabatic compressibilities of dodecylpolyoxyethylene glycol monoethers in water at 5, 25, and 45°C

Density and ultrasonic velocity measurements were made on a series of dilute aqueous solutions ofn-C ₁₂ H ₂₅ O (CH ₂ CH ₂ O) _n H (n=6,7 and 8) at 5, 25, and 45°C. The partial molal volumes (V) and adiabatic compressibilities (K)of the solutes were independent of the concentration in the micellar solutions. This finding suggests that the mode of aggregation does not change over the concentration range studied. Larger V and K were found for the CH ₂ CH ₂ groups in micelles than in water, and the micellar core was shown to be liquidlike. The V and K of the monomeric surfactants could not directly be measured because of the very low c.m.c.'s. The infinite dilution values V^° and (K^°) were, however, estimated from the V^° and K^° for the constituent groups on the basis of additivity. Thus, sharp increases were found in both V and K on micellization, which was interpreted in terms of dehydration effects.     

Aqueous solutions of azoniaspiroalkane halides. VI. Apparent molal volumes and apparent molal heat capacities of chlorides and iodides

Densities and heat capacities of aqueous solutions of azoniaspiroalkane halides, (CH₂) _n N⁺ (CH₂) _n X^– (where X=Cl, I andn=5,6), have been measured at 25°C using a flow densimeter and a flow microcalorimeter. The limiting apparent molal volumes (ø _v ) and apparent molal heat capacities (ø _cp ) obtained from these data are compared with those of the azoniaspiroalkane bromides and the corresponding tetraalkylammonium halides. The concentration dependence of ø _v and ø_cp are examined for clues on the influence of solute hydration, structure, and conformational flexibility on the excess functions of quaternary ammonium halides.     

Apparent molal volumes of aqueous solutions of bis-tetraalkylammonium salts at 25°C: Methylene-group contribution to the limiting molal volume

Densities of aqueous solutions of a series of polymethonium chloride and bromide salts (CH₃)₃–N–(CH₂)_n–N–(CH₃)₃X₂ have been measured at 25°C. Apparent molal volumes have been calculated, and methylene-group contributions to the limiting apparent molal volumes °_v have been estimated. Constant values of the methylene-group contribution of 16.5 and 17.0 cm³-mole^–1 were obtained for the bromide and chloride salts, respectively. These values are consistent with methylene-group contributions reported for other series of organic electrolytes.     

Solution thermodynamics of first-row transition elements. 4. Apparent molal volumes of aqueous ZnSO4 and CuSO4 solutions from 15 to 55°C

The apparent molal volumes of ZnSO ₄ and CuSO ₄ have been determined from density data over the temperature range 15–55°C and concentration range 0–15 molal. The volume data have been fitted to the Pitzer formalism over the entire temperature and concentration range. The volume changes for the formation of ZnSO ₄ and CuSO ₄ ion pairs have been estimated over the temperature range covered and the partial molal volumes of ZnSO ₄ and CuSO ₄ ion pairs have been derived. The results were used to explain the hydration structure of the ion pair. UV spectral effects accompanying a change of temperature in the 15–65°C range in CuSO ₄ solution indicate direct coordination of sulfate anion to the cupric cation. The process is favored by an increase in temperature.     

The PVT properties of concentrated aqueous electrolytes IX. The volume properties of KCl and K2SO4 and their mixtures with NaCl and Na2SO4 as a function of temperature

The densities of KCl and K₂SO₄ were measured from dilute solutions to saturation from 5 to 95°C. The data were combined with literature data to produce density and apparent molal volume, V_φ, equations from 0 to 100°C and to saturation. The standard deviations of the density equations were 30×10⁻⁶ g-cm⁻³ and 32×10⁻⁶ g-cm⁻³, respectively, for KCl and K₂SO₄. Pitzer equations were used to fit the V_φ data. The resulting infinite dilute partial molal volumes, V^o, were in reasonable agreement with literature data. The densities of the mixtures of the six combinations of the salts KCL, K₂SO₄ NaCl and Na₂SO₄ were measured at I=2.0 and t=5, 25, 55 and 95°C. The resulting volumes of mixing were fitted to equations of the form

Molal volume of aqueous boric acid-sodium chloride solutions

The apparent molal volume φ _v of boric acid has been determined in various sodium chloride solutions at 0 and 25°C from precise density measurements. Similar to its behavior in pure water, the φ _v of boric acid in NaCl solutions is a linear function of the concentration. The infinite dilution φ _v ^° and the slope S _v ^* of B(OH)₃ are larger in NaCl solutions than in pure water. NaCl appears to be able to dehydrate B(OH)₃ and cause an increase in B(OH)₃-B(OH)₃ interactions. The mean apparent molal volumes Φ _v of the B(OH)₃−NaCl solutions are predicted from pure water data using a modification of Young's rule for electrolyte-nonelectrolyte mixtures and are compared to the directly measured values. A similar treatment was carried out on the density data of acetic acid-sodium chloride solutions. The modified Young's rule was found to give a good first approximation of the mean apparent molal volumes of nonelectrolyte-electrolyte systems. The deviations from the Young's rule approximation are studied as excess volumes of mixing boric acid and NaCl solutions. Taken from a thesis submitted by Gary K. Ward in partial fulfillment of the requirements of the Master of Science degree, University of Miami, Miami, Florida 33149. Scientific Contribution Number 1731 from the University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida 33149.     

Apparent molal heat capacities and volumes of pyridine and methyl-substituted pyridines in aqueous solution at 25°C

We have made calorimetric measurements leading to apparent molal heat capacities of pyridine and four methyl-substituted pyridines in aqueous solution at 25.0°C. Measurements of densities of the same solutions have led to apparent molal volumes. The results are as follows: pyridine, _C ^° = 305.7 J–°K^–1-mole^–1 and _V ^° = 77.5 cm³-mole^–1; 2-methylpyridine, _C ^° = 370.0 J–°K^–1-mole^–1 and _V ^° = 94.3 cm³-mole^–1; 3-methylpyridine, _C ^° = 380.2 J–°K^–1-mole^–1 and _V ^° = 93.7 cm³-mole^–1; 4-methylpyridine, _C ^° = 378.9 J–°K^–1-mole^–1 and _V ^° = 94.3 cm³-mole^–1; 2,6-dimethylpyridine, _C ^° = 441.8 J–°K^–1-mole^–1 and _V ^° = 109.9 cm³-mole^–1. These _C ^° and _V ^° values are discussed in terms of effects of substitution of CH₃-for H– in the various solute molecules.The research reported here was carried out in the Department of Chemistry, University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4.     

Hydrophobic interactions: Ionic mobilities of tetraphenylphosphonium chloride in aqueous solutions at 25°C

The present study provides systematic data of conductivity, transference number and apparent molal volume for Ph₄PCl in water at 25°C over a concentration range 0.005–0.5 mol-l^–1. Transference numbers have been measured by labelling the migrating species with radiotracers¹⁴C for Ph₄P⁺ and³⁶Cl for the anion. An unexpected concentration depenence for the transference numbers is observed that deviates markedly from that of a simple 1:1 electrolyte. Excess transport properties have been interpreted in terms of cation dimerization induced by hydrophobic interactions.     

Mixtures of 1-1 electrolytes: Densities and excess volumes of aqueous NaCl-NaBr solutions at 25°C

The relative densities and excess volumes of mixing are reported for the system consisting of aqueous NaCl and NaBr at 25°C at constant ionic strengths of 0.5, 1, 2, 3, and 4 mol kg^–1 of water. The measurements of densities are precise to 3 · 10^–6 g cm^–3. The densities, apparent molal volumes and excess volumes are analysed with the virial coefficients approach with excellent accuracy. The excess volumes are positive throughout.

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Mischung von 1 : 1-Elektrolyten: Dichten und Excess-Volumina von wäßrigen NaCl-NaBr-Lösungen bei 25°C

Zusammenfassung Die relativen Dichten und Excess-Volumina der Mischung werden für das System wäßriges NaCl-NaBr bei 25°C und einer konstanten Ionenstärke von 0.5, 1, 2, 3 und 4 mol kg^–1 Wasser berichtet. Die Dichtemessungen haben eine Genauigkeit von 3 · 10^–6 g cm^–3. Die Dichten, die effektiven molalen Volumina und die Excess-Volumina werden von der Virialkoeffizienten-Methode ausgezeichnet wiedergegeben. Die Excess-Volumina sind durchwegs positiv.

     

Enthalpies of solution,partial molal heat capacities and apparent molal volumes of sugars and polyols in water

Integral enthalpies of solution of some sugars and polyols in water at low concentrations have been determined calorimetrically at 25 and 35°C. These data have been used to derive heat capacities of solution C°_p at 30°C. Partial molal heat capacities C°_p,2 have been obtained by combining C°_p with C _p,2 ^* , the heat capacity of pure solid compounds. Apparent molal volumes have been obtained from density data. The sugars as well as polyols show significantly high positive C°_p and C°_p,2 values. The results have been explained in terms of a specific hydration model. The effect of substitution of-OH by glycosidic-OCH₃ and of-CHOH by deoxy-CH₂ are also discussed.     

Isentropic partial molal compressibilities of alcohols in propylene carbonate at 25°C

The isentropic coefficients of compressibility of the homologous series of alcohols and diols R _n CH₂OH (n=2–6), CH₃CHOHR _n (n=1–5), 1,2-propanediol, 1,3- 1,4- and 2,3-butanediol, 1,5-pentanediol, and 1,7-heptanediol dissolved in propylene carbonate have been measured at 25°C. Isentropic partial molal compressibilities and group partial molal compressibilities at infinite dilution have been evaluated. The isentropic partial molal compressibilities of these alcohols and diols have been compared with the corresponding values in water. This comparison shows that the values in propylene carbonate are higher than in water by a factor of 10 due to an increased compressibility of the solvation sheath around nonpolar groups in PC.     

The volume and compressibility change for the formation of transition metal sulfate ion pairs at 25°C

The apparent molal volume and adiabatic compressibilities of some transition metal (Mn²⁺, Co²⁺ Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) sulfates have been determined at 25°C. Values of to 11.4 cm³-mole^–1 and to 31.3 × 10^–4cm³-mole^–1-bar^–1 at 1 atm were found for the formation of the transition metal sulfate ion pairs. These results are in good agreement with the values obtained from the high-pressure conductance measurements of Fisher et al., Shimizu et al., and Taniguchi et al. The volume and compressibility data indicate that 3.1±0.7 water molecules are lost when transition metals form ion pairs with SO ₄ ^2– . The fractions of inner-sphere ion pairs (20%) estimated in this study are in good agreement with the values obtained from ultrasonic measurements.     

Volume and compressibility changes of complex formation between 18-Crown-6 and NaCl,KCl, and CsCl in water

The apparent molal volumes and compressibilities of NaCl, KCl, and CsCl in mixtures of 18-Crown-6 and water have been calculated from density and speed-of-sound measurements at 25°C. The partial molal volumes and compressibilities of the salts when all cations have formed complexes with 18-Crown-6 molecules have been evaluated. The sign and magnitude of the volume and compressibility changes of complex formation strongly suggest that the charge of the cation becomes very effectively screened by the crown ether.