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.     

Enhanced isospin dependence of the empirical particle-hole effective interaction

The separation betweenT=0 andT=1 centroids of the empirical effective interaction is fairly large for the (d ₃ ^2/−1 f _7/2)JT particle-hole interaction as compared to nearby (f _7/2)² JT and (d _5/2)² JT particle-particle interactions. This interesting feature of the empirical effective interaction is shown to arise as a consequence of renormalization of the effective interaction as one truncates the configuration space from (s−d)⁻¹(f−p)¹ to (d ₃ ^2/−1 f _7/2) and from (f−p)² and (s−d)² configurations to (f _7/2)² and (d _5/2)² respectively.     

Flüssig-Flüssig-Gleichgewicht und Dichten der koexistierenden Phasen des Systems Wasser-Methanol-Dichlormethan im Bereich zwischen 20 und 90 °C

This paper presents liquid liquid equilibria and densities of the coexisting phases for the system water-methanol-dichloromethane in the temperature range between 20 and 90 °C. 63 connodes, structured in isothermal datasets, have been measured. For each of the isothermal datasets a regression with the UNIQUAC as well as the NRTL model has been made. Both models describe the data within the experimental error. Simultaneous fit of all datas leads to unacceptable high deviations from experimental values for both the UNIQUAC and the NRTL modell. The extension of the UNIQUAC equation with a two parameter hyperbolic temperature function for the interaction parameters yields significantly better results as the original equation when applied to the fit of all available data.

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Verzeichnis der verwendeten Zeichen a Parameter zur Beschreibung der Temperaturabhängigkeit für die NRTL- bzw. UNIQUAC-Gleichung - b Parameter zur Beschreibung der Temperaturabhängigkeit für die NRTL- bzw. UNIQUAC-Gleichung - g _ji -g _jj Wechselwirkungsparameter in der NRTL-Gleichung - G ^E FreieGibbs'sche Exzeßenthalpie - p _ij generalisierter Wechselwirkungsparameter der NRTL- bzw. UNIQUAC-Gleichung - q _i relativevan der Waal'sche Oberfläche der Komponentei - r _i relativesvan der Waal'sches Volumen der Komponentei - R allgemeine Gaskonstante - T absolute Temperatur - u _ji -u _jj Wechselwirkungsparameter der UNIQUAC-Gleichung - x Molenbruch - z Koordinationszahl - _ij Non-randomeness Parameter der NRTL-Gleichung - _i Oberflächenbruch der Komponentei - _i Volumenbruch der Komponentei     

Some NP-complete problems in linear programming

Degeneracy checking in linear programming is NP-complete. So is the problem of checking whether there exists a basic feasible solution with a specified objective value.     

Electron microscopic studies of SBS block copolymers I. A method to study the temperature dependence of phase separation

The potential applicability of a Film Formation Method of Crystal Growth to the study of morphological aspects of amorphous polymers was investigated using transmission electron microscopic techniques. A wide variety of morphologies of styrene-butadiene-styrene triblock copolymer can be achieved by varying the solvent power and film preparation temperatures. The effect of film preparation temperature indicates that below 100 °C (the glass transition temperature of polystyrene), there is very little change in the size of domains; above 100 °C a drastic change in morphology is observed. Not only is there rapid coarsening of both the constituent phases of the polymer above 100 °C, but also an intermixing of both phase components of the block copolymer. It was demonstrated that some monomeric materials are effective in maintaining the original morphology of the film; i. e. phase mixing is prevented.     

Thermodynamic parameters for the protonation of carboxylic acids in aqueous tetraethylammonium iodide solutions

The protonation constants of 21 carboxylic acids (formic, acetic, propionic, benzoic, phenoxyacetic, salicylic, oxalic, malonic, succinic, itaconic, malic, tartaric, oxydiacetic, thiodiacetic, thiodipropionic, phthalic, maleic, citric, 1,2,3-tricarboxylic, 1,2,4-tricarboxylic and 1,2,4,5-tetracarboxylic), have been determined potentiometrically, by pH-metric measurements, at several temperatures and ionic strengths, 5T55°C, 0<11 mol-dm^–3, using tetraethylammonium iodide as background salt. General equations for the dependence on ionic strength of thermodynamic parameters have been found. The statistical significance of results and the possibility of using a simple model for the thermodynamics of carboxylic acids protonation, is discussed.     

Viscosity behavior of benzoic acid and benzoate ion in aqueous solution

Relative viscosities of aqueous solutions of benzoic acid and benzoates of lithium, sodium, potassium, and ammonium are measured. In the temperature range 25–35°C, the Jones-Dole viscosityB coefficients of the benzoate ion decrease with increasing temperature, indicating a net structure-making effect. The somewhat larger value of theB coefficient for the benzoate ion than that for the benzoic acid molecule confirms similar behavior for the acetate ion and acetic acid in aqueous solutions although the effect is much smaller.     

Spectral‐Polarization Contrasts in the Problems of Remote Sensing

The results of the investigation of the angular and spectralpolarization characteristics of 4501080nm radiation reflected from the surfaces of natural (leaves of trees, bark) and artificial (colored smooth surface, fabric) objects are discussed. Based on a study of the contrasts between these characteristics, we have determined the most informative spectralpolarization characteristics and the spectral and angular intervals the use of which in remote optical observations of objects would allow their most effective discrimination.     

Strong near-epoch dependence

We introduce a new class of dependent sequences of random variables, which is a subclass of near-epoch dependent sequences, but can also be approximated by mixing sequences. For this kind of sequences of random variables, we call them strong near-epoch dependent sequences, ap-order,p > 2, (maximum) moment inequality is established under weaker dependence sizes.     

Dependence Between Extreme Values of Discrete and Continuous Time Locally Stationary Gaussian Processes

The maximum of a continuous, locally stationary Gaussian process which satisfies Bermans condition on the long range dependence is compared with the maximum of this process sampled at discrete time points. These two extreme values are asymptotically totally dependent if the grid of the discrete time points is sufficiently dense, and asymptotically independent if the the grid points are sparse.AMS 2000 Subject Classification. Primary—60F05, Secondary—60G15