Enthalpies of reaction of calcium chloride and sodium oxalate in aqueous solution of Tween 80

The heats of mixing of dilute calcium chloride and sodium oxalate solutions in water and aqueous solutions of a nonionogenic surfactant, namely, polyoxyethylene (20) sorbitan monooleate (Tween 80) containing 1–5 wt % of the dissolved substance were measured at 298.15 K. The heats of dilution of calcium chloride solutions were determined, and the enthalpies of precipitation of calcium oxalate in water and surfactant solutions were calculated. The surfactant concentration was found to have almost no effect on the enthalpies of the processes under study; rather, it modifies the shape of the resultant deposit by preventing the agglomeration of calcium oxalate particles.     

Enthalpies of reaction of calcium chloride and sodium oxalate in an aqueous NaCl solution

The heats of mixing of dilute aqueous solutions of calcium chloride and sodium oxalate with additions of 1–5 wt % NaCl at 298.15 K and the heats of dilution of calcium chloride solutions were measured. Increasing the sodium chloride content in a solution noticeably increases the time of precipitation of calcium oxalate. A fine precipitate of CaC₂O₄ formed in solutions containing 3 and 5 wt % NaCl is difficult to remove from the parts of a calorimeter cell. The enthalpies of precipitation of CaC₂O₄ depend slightly on the content of the “background electrolyte,” whereas the enthalpies of dilution, owing to ion association, significantly decrease in magnitude and become positive in a 5% NaCl solution. The “standard” enthalpy of precipitation in water, determined by extrapolation of the experimental values to the zero concentration of the background electrolyte, differs noticeably from the enthalpy of precipitation in water.     

The enthalpies of interactions of Ca2+(aq) and C2O 4 2− (aq) ions in complexon solutions: Competition between complexation and precipitation

The thermal effects of mixing of aqueous calcium chloride with sodium citrate and ethylenedi-aminetetraacetate in the absence and presence of sodium oxalate have been measured at 25°C. The thermal effects of dilution of aqueous calcium chloride solutions were determined. The thermal effects of calcium oxalate precipitation and formation of calcium complexes with citrate and ethylenediaminetetraacetate ions were calculated. The 1% solution of sodium citrate inhibited the formation of CaC₂O₄ (s); in a 1% solution of sodium ethylenediaminetetraacetate with [Ca²⁺][C₂O ₄ ^2? ] > 10^?5, the endothermal formation of the [CaEdta]^2? complex quickly changed to exothermal precipitation. The 3 and 5% solutions of complexons showed a pronounced inhibiting effect on the formation of urinary stones even when the concentration of calcium and oxalate ions in solution exceeded the product of solubility of CaC₂O₄ by four and more orders of magnitude.     

Enthalpies and heat capacities of dissolution for calcium chloride and sodium oxalate

The heats of solution at 25 and 40°C in water are measured for various concentrations of calcium chloride and sodium oxalate. The standard enthalpies of solution are determined using the Debye-Hückel second approximation. The heat capacity change upon dissolution and the partial molal heat capacities of electrolytes at infinite dilution are calculated.     

Thermodynamic properties of transition metals in aqueous solution: 3. The heats of mixing aqueous solutions of CdCl2, NiCl2 and ZnCl2 with NaCl at varying ionic strength at 25°C

The heat of dilution of aqueous solutions of ZnCl₂ and the heats of mixing H _m of aqueous solutions of CdCl₂, NiCl₂, and ZnCl₂ with NaCl solutions were measured at 25°C. The heats of mixing were made at constant ionic strengths of 0.5, 1.0, and 3.0 molal. The excess enthalpy equations of Pitzer were then fitted to the resulting heats of dilution and heats of mixing data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system.     

Thermodynamic study of poly(N-vinyl caprolactam) hydration at temperatures close to lower critical solution temperature

The lower critical solution temperature of aqueous solutions of poly(N-vinyl caprolactam) falls in the 305–307 K range and depends on the molecular weight of the polymer. The thermodynamic functions of mixing at 298 K have been calculated from measurements of vapor pressures and heats of dissolution and dilution. Partial Gibbs energy, partial enthalpy, and partial entropy of mixing were negative over the entire range of composition. Increasing temperature resulted in a decrease in the exothermal character of mixing. Excessive heat capacity values, calculated from the dependencies of enthalpy of mixing on temperature, were positive over the entire composition range. Heat capacity of dilute solutions was measured at 298 K and partial heat capacity of poly(N-vinyl caprolactam) at infinite dilution was shown to be positive. The data obtained point out the hydrophilic and hydrophobic hydration of poly(N-vinyl caprolactam) in aqueous solutions. Hydrophobic hydration dominates at temperatures close to binodal curve. As a result, the mutual mixing of the polymer with water is decreased and phase separation takes place.     

Thermochemistry of solvation and complexation in the Cu(NO3)2-water-ethanol-L-α-alanine system at 298.15 K

The heats of mixing of aqueous solutions of copper(II) nitrate and sodium alaninate and the heats of dilution of an aqueous solution of sodium alaninate in water-ethanol mixtures were calorimetrically measured at 298.15 K. The enthalpies of transfer of α-alaninate from water into water-alcohol mixtures and the standard molar enthalpies of the reaction of copper(II) complexation with α-alaninate ion in the mixtures under study are calculated. The resulting enthalpy parameters are compared with those of the similar system containing synthetic β-alanine, which was studied earlier.     

Limiting partial molar excess enthalpies by flow calorimetry: Some organic solvents in water

A Picker flow microcalorimeter was employed in conjunction with asymmetric syringe-type pumps to measure heats of mixing of highly dilute aqueous solutions of organic solvents. These data were used in turn to determine limiting partial molar excess enthalpies of the examined solvents in water. The measurements were carried out at 298.15 K for 29 common, oxygen and/or nitrogen containing solvents exhibiting complete miscibility with water. Except for only one compound, formamide, the limiting partial molar excess enthalpies are exothermic indicating that the process of dissolution is energetically favored. Comparison to literature data (in most cases to solution enthalpies at infinite dilution measured by batch calorimetry) proved the technique applied to be sufficiently accurate.     

New Physico-chemical Properties of Water Induced by Mechanical Treatments. A calorimetric study at 25°C

An extensive thermodynamic study has been carried out on aqueous solutions, obtained through the iteration of two processes: a dilution 1:100 in mass and a succussion. The iteration is repeated until extreme dilutions are reached (less than 1⋅10^–5 mol kg^–1 ) to the point that we may call the resulting solution an 'extremely diluted solution'. We conducted a calorimetric study, at 25°C, of the interaction of those solutions with acids or bases. Namely, we measured the heats of mixing of acid or basic solutions with bidistilled water and compared them with the analogous heats of mixing obtained using the 'extremely diluted solutions'. Despite the extreme dilution of the latter solutions, we found a relevant exothermic excess heat of mixing, excess with respects to the corresponding heat of mixing with the untreated solvent. Such an excess has been found in about the totality of measurements, and of a magnitude being well beyond one that could arise any issue of sensibility of the instrumental apparatus. Here we thus show that successive dilutions and succussions can permanently alter the physico-chemical properties of the solvent water. The nature of the phenomena here described still remains unexplained, nevertheless some significant experimental results were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

New physico-chemical properties of extremely diluted aqueous solutions

The 'extremely diluted solutions', anomalous solutions prepared through the iteration of a process of dilution and succussion, have been studied with the aim of obtaining information about the influence of the preparation method on the water structure of the solutions. We measured the heats of mixing of basic solutions with such 'extremely diluted solutions', and their electrical conductivity, comparing with the analogous heats of mixing, electrical conductivity of the solvent. We found some relevant exothermic excess heats of mixing, and higher conductivity than those of the untreated solvent. The heats of mixing and electrical conductivity show a good correlation, underlining a single cause for the behaviour of the extremely diluted solutions. This revised version was published online in July 2006 with corrections to the Cover Date.     

A flow microcalorimeter for measuring the heats of mixing of binary liquids by A continuous process

In order to measure heats of mixing or heats of dilution for many solutions by a continuous process accurately, a twin conduction type flow microcalorimeter has been constructed, improving the design of the same type of calorimeter reported previously. The thermal stability of the heat sink was enhanced by enlarged contact area of the main heat sink block with a thermostated water bath. Mixing efficiency of the mixing cell and the stability of the base line were improved by the use of a new mixing cell having a long mixing zone and symmetrically arranged sample and reference cells. Waiting time for establishment of thermal steady state was also reduced by sandwiching each of the cell by a pair of wide thermopiles plates and a pair of sub-blocks. Heats of dilution of aqueous urea solutions were measured by a continuous process, and results obtained well agreed with accepted values by Guckeret al. The accuracy and thermal resolution in this calorimeter were estimated to be less than 0.05% and 3 J·s^–1.The authors are grateful to Professor S. Murakami of Osaka City University for helpful discussion.     

Enthalpies de dissolution des halogenures de rubidium et cesium dans les solutions aqueuses d'acides halogenes correspondants

The heats of dissolution and dilution of rubidium and cesium halides in aqueous solutions of the corresponding halogen acid have been measured for a wide range of acid and salt concentrations. The hydration numbers of Rb⁺ and Cs⁺ have been determined from the heats of dissolution at infinite dilution.     

Study on the capacities,heats of dilution and properties of concentrated potassium carnallite solutions at 298.15 K

The heats of dilution of the infinitesimally dilute potassium carnallite solutions at 298.15 K have been studied by continuous titration from 1.8942 to 0.01044 mol·kg^?1, and an equation for the curve of heats of dilution has been fitted. It was shown that the enthalpy of dilution for the same concentration of the carnallite solution is equal to the sum of those of KCl and MgCl₂ solutions. The equation for the curve of enthalpy of dilution corresponds to that of natural carnallite.     

Determination of calcium in biological material The use of calcein as an indicator in the edta titration

The EDTA titration of calcium using the change in fluorescence of Calcein indicator under ultraviolet illumination at the end-point was very satisfactory for essentially pure calcium chloride solutions. In order to use this method for biological samples, it was found best to separate the calcium by an oxalate precipitation at a pH of 4.7, convert the calcium oxalate to calcium carbonate, and dissolve the calcium carbonate in hydrochloric acid.     

α-氨基酸与氯化铷在水溶液中焓相互作用参数

The mixing enthalpies of aqueous heavy rare alkali metal chloride RbC1 solutions with aqueous α-amino acid (Loglycine, L-alanine and α-aminobutyric acid) solutions, as well as the dilution enthalpies of RbC1 and α-amino acid solutions in pure water had been measured at 298.15K. The transfer enthalpies of RbCI from pure water to aqueous α-amino acid solutions could be obtained from these data. The enthalpic pair interaction parameters of RbC1 with α-amino acid in water have been evaluated according to the McMillan-Mayer theory and discussed in terms of the electrostatic interaction, structure interaction and Savage-wood group additivity mode.     

A Study of Calcium Chloride Purification

Two methods of calcium chloride purification were studied: crystallization from aqueous solutions and joint precipitation of impurities from aqueous solutions onto inorganic collectors (hydrated aluminum or zirconium oxides). The purification factors were calculated and a high efficiency of purification of calcium chloride solutions with hydrated zirconium dioxide as collector was established.     

Freezing points and related properties of electrolyte solutions. III. The systems NaCl−CaCl2−H2O and NaCl−BaCl2−H2O

The freezing temperatures of aqueous calcium chloride and barium chloride and their mixtures with sodium chloride were measured at equivalent molalities of 0.1 to 1.5 mole-kg^?1. Osmotic and activity coefficients of the mixtures were calculated at the freezing points of the mixtures. From the freezing points and calorimetric enthalpies of mixing of sodium chloride-magnesium chloride solutions, osmotic and activity coefficients were calculated at 298°K. Agreement of the calculated properties with isopiestic and electrochemical measurements at 298°K is excellent.     

INDUCTION OF CRYSTALLIZATION OF SPECIFIC CALCIUM OXALATE HYDRATES IN MICELLAR SOLUTIONS OF SURFACTANTS

ABSTRACT

The influence of octaethylene glycol mono-n-hexadecyl ether (C₁₆EO₈) and sodium dodecyl sulphate (SDS) on the crystallization of calcium oxalate from 0.3 mol dm^?3 sodium chloride solutions has been investigated. The critical micellar concentration (CMC) of C₁₆EO₈ in water and 0.3 mol dm^?3 NaCl was determined by surface tension measurements (CMC_H2O=CMC_NaCl = 7.2.10^?6 mol dm^?3). The kinetics of precipitation of calcium oxalate was followed by Coulter counter, and solid phases were characterized by polarized microscopy, thermal analysis and X-ray powder diffraction patterns. Under the precipitation conditions employed, the thermodynamically stable monohydrate, CaC₂O₄?H₂O (COM) was the predominant crystalline form. In the presence of micellar solutions of C₁₆EO₈ precipitation of this phase was facilitated as evidenced by higher initial precipitation rates and higher precipitate volume and number of particles, as compared to the controls. Micellar solutions of 50S retarded precipitation but induced crystallization of calcium oxalate dihydrate, CaC₂O₄?(2+×)H₂O (COD, x≤0.5). Thus at c(SDS>CMC the precipitates contained ≥85 mass % COD. The results are discussed in relation to previously reported data on the precipitation of calcium oxalate in the presence of dodecyl ammonium chloride     

Molar excess enthalpies for aqueous solutions of 2-chloroethanol and 2-bromoethanol at 298.15 K

Heats of mixing for two aqueous solutions of haloalcohols, 2-chloroethanol and 2-bromoethanol, have been measured for the whole composition range at 298.15 K with an LKB 2107 flow calorimeter. The mixing is endothermic for these solution, except for highly water-rich region. The enthalpic virial coefficient has been evaluated from the data in dilute aqueous solution.     

Seawater—A test of multicomponent electrolyte solution theories. II. Enthalpy of mixing and dilution of the major sea salts

In a continuing effort to predict the physicochemical properties of seawater from the properties of single aqueous electrolyte solutions, the pairwise heats of mixing at constant molal ionic strength,I=1.0 ional, have been determined for the six possible pairs of salts from the set (NaCl, Na₂SO₄, MgCl₂, MgSO₄) at 30°C. In addition, heats of dilution for two aqueous solutions formed from these salts and havingI=1.0 ional have been determined at 30°C. In order to present the most thermodynamically consistent results, it was found necessary to apply a correction term to the relative apparent equivalent enthalpies given in the literature at 30°C. These correction terms derived from a consideration of published results on heats of dilution at very low concentrations. Further, in order to make predictions for seawater at 25°C, it was deemed desirable to refit existing heat-capacity data. The heats relative apparent equivalent enthalpies for the two mixtures mentioned as well as for seawater. The estimates are based on the theoretical equation of Reilly and Wood for charge-asymmetric mixtures which derives from the work of Friedman. In the most applicable cases, the estimates agree with experimental relative apparent equivalent enthalpies to within 5%. In general, the results substantiate the theoretical equation.Taken in part from the Ph.D. dissertation of W. H. Leung, University of Miami, Miami, Florida 33149.