Effect of pressure on the solubility of naphthalene in water at 25°C

Solubility of naphthalene in water was measured at 25°C and pressures up to 200 MPa. The solubility decreased with increasing pressure. From the pressure coefficient of the solubility, the volume change V accompanying the dissolution was estimated as 13.8±0.4 cm ³ -mol ^–1 . Further we estimated the volume change V _CH accompanying hydrophobic hydration as –0.1±0.6 cm ³ -mol ^–1 using the V value, the molar volume of crystalline naphthalene, and the partial molar volume of naphthalene in n-heptane. This V _CH is much larger (i.e., less negative) than that for hydrophobic hydration of alkyl-chain compounds and suggests that the hydration structure of naphthalene differs from that of alkyl-chain compounds.     

Complexation,solubilities and thermodynamic functions for cerium(III) fluoride-water system

The solubility, solubility product and the thermodynamic functions for the CeF₃–H₂O system have been measured using the radiometric, conductometric and potentiometric techniques. The radiometric values for the solubility and solubility product, the lowest and more acceptable for reasons cited in previous papers, are 3.14·10^–5 M and 2.17·10^–17 respectively. The enthalpy change measured by the conductometric method is almost twice as that obtained by potentiometric method due to abnormal conductances registered at higher temperatures. The average values for H^o and G^o and S^o at 298 K are 53.0±17.4, 91.7±4.0 and –129.7±58.2 KJ·mol^–1 respectively. The positive values for H^o and G^o and the negative value for S^o are indicative of the low solubility of this salt in water. The stability constants for the mono- and difluoride complexes of Ce(III) have been determined potentiometrically using unsaturated solution mixtures of Ce(III) and F^–. These values for CeF⁺ and CeF ₂ ⁺ are 997±98 and (1.03±0.44)·10⁵, respectively. Studies on pH dependence of the solubility shows that the solubility reaches a minimum value at a pH of about 3.2.     

Dissociation quotient of benzoic acid in aqueous sodium chloride media to 250°C

The dissociation quotient of benzoic acid was determined potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of benzoic acid/benzoate solutions was measured relative to a standard aqueous HCl solution at seven temperatures from 5 to 250°C and at seven ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and selected literature data were fitted in the isocoulombic (all anionic) form by a six-term equation. This treatment yielded the following thermodynamic quantities for the acid dissociation equilibrium at 25°C and 1 bar: logK_a=–4.206±0.006, H _a ^o =0.3±0.3 kJ-mol^–1, S _a ^o =–79.6±1.0 J-mol^–1-K^–1, and C _p;a ^o =–207±5 J-mol^–1-K^–1. A five-term equation derived to describe the dependence of the dissociation constant on solvent density is accurate to 250°C and 200 MPa.     

Acid association quotients of bis-tris in aqueous sodium chloride media to 125°C

The ionic strength and temperature dependencies of the molal acid association quotients of 2,2-Bis(hydroxymethyl)-2,2,2-nitrilotriethanol (also abbreviated as bis-tris) were determined potentiometrically in a concentration cell fitted with hydrogen electrodes. The emf was recorded for equimolal bis-tris/bis- trisHCl buffer solutions from 5 to 125°C at approximately 25°C intervals, and at nine ionic strengths from 0.05 to 5.0m (NaCl). The molal association quotients, combined with infinite dilution values from the literature, are described precisely by a seven parameter equation which yielded the following thermodynamic quantities at infinite dilution and 25°C: logK=6.481±0.003, H ^o =–28.5±0.2 kJ-mol ^–1 , S ^o =28.5±0.8 J-K ^–1 -mol ^–1 , and C _P ^o =–22±5 J-K ^–1 -mol ^–1 . The equation incorporates a simple three term expression for logK, but requires four terms to describe the rather complex ionic strength dependence despite the reaction being isocoulombic. The molal association quotients from this study and the literature were also subjected to the Pitzer ion interaction treatment.     

Acid properties of some phosphonocarboxylic acids

Thermodynamic acid dissociation constants were determined for phosphonoacetic acid (PAA) in aqueous solution at 25°C by coulometric titrations at different ionic strengths and extrapolation of the results to I=0. The respective values are pK₁2.0, pK₂=5.11±0.04, and pK₃=8.69±0.05. The enthalpy and entropy of dissociation for the second and the third dissociation steps, determined from the temperature dependence of pK's, are H ₂ ^o =0.2±0.3 kcal-mole^–1, S ₂ ^o =22.6±0.9 e.u., H ₃ ^o =1.3±0.4 kcal-mole^–1, and S ₃ ^o =11.7±0.4 e.u. Phosphorus-31 and carbon-13 NMR studies of PAA solutions as a function of pH gave the deprotonation sequence of the triacid. Acidity constants were also determined for phosphonoformic acid, 2-phosphonopropionic acid, and 3-phosphonopropionic acid at an ionic strenght of 0.05.To whom correspondence should be addressed.     

Thermodynamics of the weak interaction between samarium cation and xylitol in water: A chemical model

The thermodynamic characterization of the weakly complexed model system Sm³⁺-xylitol has been carried out. The standard Gibbs energy enthalpy, entropy, volume and heat capacity of complexation of Sm³⁺ by xylitol have been determined in water at 25°. The stability constant and the enthalpy change have been simultaneously determined by using a calorimetric method. The thermodynamic properties characterizing solely the specific interaction between the cation and the complexing sequence of hydroxyl groups of the ligand have been isolated. The stability constant and the volume of complexation have also been estimated from a similar treatment of the apparent molar volumes. It was found that the reaction between Sm³⁺ and the complexing site of xylitol in water is characterized by: K = 8.1, _rG^o = –5.2 kJ-mol^–1, _rH^o = –13.7 kJ-mol^–1, T_rS^o = –8.5 kJ-mol^–1, _rV^o = 8.8 cm³-mol^–1 and _rC _p ^o = 51 J-K^–1-mol^–1.     

Dissociation quotients of oxalic acid in aqueous sodium chloride media to 175°C

The first and second molal dissociation quotients of oxalic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. The emf of oxalic acid-bioxalate solutions was measured relative to an HCl standard solution from 25 to 125°C over 25^o intervals at nine ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a five-term equation that yielded the following thermodynamic quantities at infinite dilution and 25°C: logK_1a=–1.277±0.010, H _1a ^o =–4.1±1.1 kJ-mol^–1, S _1a ^o =38±4 J-K^–1-mol^–1, and C _p,1a ^o =–168±41 J-K^–1-mol^–1. Similar measurements of the bioxalate-oxalate system were made at 25^o intervals from 0 to 175°C at seven ionic strengths from 0.1 to 5.0m. A similar regression of the experimentally-derived and published equilibrium quotients using a seven-term equation yielded the following values at infinite dilution and 25°C: logK_2a=–4.275±0.006, H _2a ^o =–6.8±0.5 kJ-mol^–1, S _2a ^o =–105±2 J-K^–1-mol^–1, and C _p,2a ^o =–261±12 J-K^–1-mol^–1.     

Partial Molar Volumes of Transfer of Some Amino Acids from Water to Aqueous Glycerol Solutions at 25°C

Apparent molar volumes of glycine, DL--alanine, L-valine, L-leucine, and L-phenylalanine in 0.5, 1.0, 2.0, 3.5, and 5.0 m _B (mol-kg^–1) aqueous solutions of glycerol have been obtained from solution densities at 25°C using precise vibrating-tube digital densimeter. The estimated partial molar volumes at infinite dilution V ^o ₂ have been used to obtain the corresponding transfer volumes _tr V ₂ ^o from water to different glycerol–water mixtures. The transfer volumes are positive for glycine and DL--alanine, and both positive and negative for the other amino acids over the concentration range studied. Interaction coefficients have been obtained from McMillan–Mayer approach and the data have been interpreted in terms of solute–cosolute interactions.     

Triiodide ion formation equilibrium and activity coefficients in aqueous solution

The equilibrium quotient for the formation of triiodide was studied as a function of temperature, 3.8–209.0°C, and ionic strength, 0.02–6.61. The best-fit value for the molal equilibrium constant at 25°C is 698±10 and the corresponding partial molal enthalphy, entropy, and heat capacity of formation are: H^o=–17.0±0.6 kJ-mol^–1, S^o=–0.6±0.3 J-K^–1-mol^–1, and C _p ^o =–21±8 J-K^–1-mol^–1. Activity coefficients of iodine were determined as a function of ionic strength (NaClO₄) at 25°C and conclusions are drawn as to the corresponding ionic strength dependence of the triiodide anion.     

Conductimetric determination of ion-association constants for calcium,cobalt, zinc,and cadmium sulfates in aqueous solutions at various temperatures between 0°C and 45°C

Thermodynamic ion-association constants for calcium, cobalt, zinc, and cadmium sulfates in aqueous solutions were determined by means of conductivity measurements at various temperatures between 0°C and 45°C. The standard Gibbs energy, enthalpy, and entropy for the reaction M ²⁺ +SO ₄ ^2– M ²⁺ ·SO ₄ ^2– (M=Ca, Co, Zn, and Cd) were calculated from the temperature dependence of the ion-association constants. The values obtained are as follows: G ₂₉₈ ^o =–12.42 kJ-mole ^–1 , H ^o =6.11 kJ-mole ^–1 , and S ₂₉₈ ^o =62.1 J- ^o K ^–1 -mole ^–1 for Ca ²⁺ ·SO ₄ ^2– ; G ₂₉₈ ^o =–12.84 kJ-mole ^–1 , H ^o =5.00 kJ-mole ^–1 , and S ₂₉₈ ^o =59.8 J- ^o K ^–1 -mole^–1 for Co ²⁺ ·SO ₄ ^2– ; G ₂₉₈ ^o =–12.65 kJ-mole ^–1 , H ^o =8.65 kJ-mole ^–1 , and S ₂₉₈ ^o =71.4 J- ^o K ^–1 -mole ^–1 for Zn ²⁺ ·SO ₄ ^2– ; G ₂₉₈ ^o =–13.28 kJ-mole ^–1 , H ^o =8.39 kJ-mole ^–1 , and S ₂₉₈ ^o =72.7 J- ^o K ^–1 -mole ^–1 for Cd ²⁺ ·SO ₄ ^2– .     

Dissociation quotients of malonic acid in aqueous sodium chloride media to 100°C

The first and second molal dissociation quotients of malonic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of malonic acid/bimalonate solutions was measured relative to a standard aqueous HCl solution from 0 to 100°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a seven-term equation. This treatment yielded the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: logK _1a =-2.852±0.003, H _1a ^/o =0.1±0.3 kJ-mol^–1, S _1a ^o =–54.4±1.0 J-mol^–1-K^–1, and C _p,1a ^o =–185±20 J-mol^–1-K^–1. Measurements of the bimalonate/malonate system were made over the same intervals of temperature and ionic strength. A similar regression of the present and previously published equilibrium quotients using a seven-term equation yielded the following values for the second acid dissociation equilibrium at 25°C: logK_2a=–5.697±0.001, H _2a ^o =–5.13±0.11 kJ-mol^–1, S _2a ^o =–126.3±0.4 J-mol^–1-K^–1, and C _p,2a ^o =–250+10 J-mol^–1-K^–1.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Enthalpies of solution of thymine and uracil in water and dimethylsulfoxide

Enthalpies of solution of thymine and uracil in water and in dimethylsulfoxide (DMSO) were measured calorimetrically in the temperature range 25–40°C. H _s ^o at 25°C for thymine and uracil in water were found to be 23.1±0.5 and 29.5±0.3 kJ-mol^–1, respectively. In DMSO, H _s ^o were 7.9±0.1 and 10.2±0.1 kJ-mol^–1, respectively. In aqueous solution C _p ^o for the two nucleic acid bases were relatively large and positive with C _p ^o of thymine being larger. Both transfer quantities H _t ^o and C _p,t ^o for the proceses H₂ODMSO for the two nucleic acid bases were negative. It is proposed that, the differences in the values obtained for the two bases is due principally to increased order in the water adjacent to the methyl group in thymine.     

The dissociation quotients of formic acid in sodium chloride solutions to 200°C

The dissociation quotients of formic acid were measured potentiometrically from 25 to 200°C in NaCl solutions at ionic strengths of 0.1, 0.3 1.0, 3.0, and 5.0 mol-kg^–1. The experiments were carried out in a concentration cell with hydrogen electrodes. The resulting molal acid dissociation quotients for formic acid, as well as a set of infinite dilution literature values and a calorimetrically-determined enthalpy of reaction, were fitted by an empirical equation involving an extended Debye Hückel term and seven adjustable parameters involving functions of temperature and ionic strength. This regressional analysis yielded the following thermodynamic quantities for 25°C: logK=–3.755±0.002, H^o=–0.09±0.15 kJ-mol^–1, S^o=–72.2±0.5 J-K^–1-mol^–1, and C _p ^o =–147±4 J-K^–1-mol^–1. The isocoulombic form of the equilibrium constant is recommended for extrapolation to higher temperatures.     

The energy of the N→O bond in 3-nitroisoxazoline N-oxide

The enthalpy of combustion of 3-nitroisoxazoline has been determined as H _c ^298.15 =–414±0.3 kcal/mole and that of 3-nitroisoxazoline N-oxide as H _c ^298.15 =–406.6±0.5 kcal/mole. From the values for the heats of combustion and evaporation, the standard enthalpies of formation have been calculated and the energy of the NO bond has been evaluated at 64±3 kcal/mole.     

Thermochemistry of Alcohols: Experimental Standard Molar Enthalpies of Formation and Strain of Some Alkyl and Phenyl Congested Alcohols

The standard molar enthalpies of formation _f H _m ^° (cr) at the temperature T = 298.15 K were determined using combustion calorimetry for di-tert-butyl-methanol (A), di-tert-butyl-iso-propyl-methanol (B), and di-phenyl-methyl-methanol (C). The standard molar enthalpies of sublimation _cr ⁸ H _m ^° of these compounds and of di-phenyl-methanol (D) were obtained from the temperature variation of the vapor pressure measured in a flow system. Molar enthalpies of fusion _cr ¹ H _m ^° of the compounds A–D and of tri-phenyl-methanol (E) were measured by differential scanning calorimeter (DSC). From these data and data available from the literature, the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) for A, (–397.0 ± 1.2); B, (–418.1 ± 2.3); C, (–34.2 ± 1.3); and D, (0.9 ± 2.1) kJ · mol^–1 were derived, which correspond to strain enthalpies (H _S) of 46.1, 114.7, 8.1, and 5.0 kJ · mol^–1, respectively.     

Potentiometric studies of the thermodynamics of iodine disproportionation from 4 to 209°C

The equilibrium constant for the disproportionation of iodine in aqueous solution was determined as a function of temperature from 3.8 to 209.0°C using emf measurements in low ionic strength media. The equilibrium constant and associated molal thermodynamic quantities at 25°C are: K₁=1.17±0.62×10^–47, H^o=273±3 kJ-mol^–1, S^o=16±9 J-K^–1-mol^–1, and C _p ^o =–1802±41 J-K^–1-mol^–1. Although the value of K₁ is in excellent agreement with a previous emf measurement at 25°C, these results conflict with the corresponding parameters obtained from the NBS tables. Moreover, at temperatures above ca. 100°C, our measured values for the equilibrium constant diverge strongly from all previous estimates and predictions.     

Study of monensin complexes with monovalent metal lons in anhydrous methanol solutions

Potentiometric and cyclo-voltammetric studies have been carried out on monensin anion (Mon^–) complexes with the alkali ions as well as with Tl⁺ and Ag⁺ in absolute methanol solutions. The log K_f values obtained for the complexity constants and corrected for the activity effects are: Li⁺, 3.3±0.1; Na⁺, 6.72±0.05; K⁺, 5.18±0.05; Rb⁺, 4.58±0.05; Cs⁺, 3.75±0.05; Tl⁺, 5.31±0.05; Ag⁺, 8.2±0.2. It is seen that for the alkali, the most stable complex is formed with Na⁺. The enthalpy and entropy of complexation with the sodium ion were found to be H^o=–5.47±0.24 kcal-mole^–1 and S^o=+12.4±0.7 e.u. The complex, therefore, is enthalpy and entropy stabilized.     

Thermodynamic parameters for the reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with 4-nitrophenylnitromethane in several aprotic solvents

Equilibrium constants K for reaction of the C-acid, 4-nitro/phenylnitromethane with 1,8-diazabicyclo [5.4.0] undec-7-ene have been determined in aprotic solvents over a range of temperature. Corresponding measurements have been made for the deuterated acid 4-NPNM-d₂. Thermodynamic parameters K, H^o and S^o, for proton and for deuteron transfers are not very differet in a given solvent, but show a considerable solvent dependence. There is an increase in magnitude of K with increase in solvent dielectric constant, a finding which is consistent with formation of an ion-pair. The range of extent of exothermicity of the reaction is quite small, –40 to-65 kJ-mol^–1, and the values of S^o (large, negative) indicate, in general, increasing solvent restriction by the product with increasing solvent polarity. A modest bathochromic solvatochromism of the product is observed as the dielectric constant increases.     

Thermodynamics of ionization of benzoic acid in water at 298°K

The standard heat of ionization of aqueous benzoic acid has been determined by solution calorimetry. The value obtained for H ^o of ionization, 0.11±0.04, is in good agreement with H ^o from other calorimetric values; 0.10±0.05 kcal-mole ^–1 is suggested to be the best value for this ionization at 298° K.     

Solubility of pentane, 2-methylbutane,and cyclopentane in liquid nitrogen at 77.4 K

The solubilities of pentane, 2-methylbutane (isopentane) and cyclopentane were measured in liquid nitrogen at 77.4 K by the filtration method. The solubilities of the C₅ hydrocarbons in liquid nitrogen at 77.4 K vary from 1.8×10^–8 mole fraction for cyclopentane, to 3.0×10^–8 mole fraction for pentane and 3.2×10^–7 mole fraction for 2-metylbutane. Correlations between the solubilities of alkanes, alkenes and cyclic hydrocarbons in liquid nitrogen, and some properties of solutes [normal boiling point T _b , enthalpy of vaporization at normal boiling point H _b and the mean of the enthalpy of vaporization and the enthalpy of melting [(H _b +H _m )/2] are presented.