Predicting the Normal Temperature Depression in Boiling of Complex Aqueous Solutions of Nonvolatile Substances

An equation for predicting the normal temperature depression in boiling of complex aqueous solutions of nonvolatile substances is considered. The constants of the equation are tabulated. The equation is compared with experimental data for a binary solution of caustic soda and sodium chloride.     

Entropy Changes in Aqueous Solutions of Non-polar Substances and in Bio-complex Formation

The entropy changes, ΔS _app, (i) for dissolution in water of non-polar substances and (ii) for protein-ligand complexation show linear dependences on the logarithm of the absolute temperature. For every compound, the slope m _(S)=ΔC _p for the line ΔS _app=f(ln T) depends on the size of the molecule and is exactly equal to the slope m _(H)=ΔC _p found in the diagram ΔH _app=f(T). This means that the slopes are rigorously proportional (with a ratio m _(S)/n _w=C _p,w) where n _w is the number of involved water molecules as determined from the enthalpy change ΔH _app=f(T). It is also worth noting that the value of n _w is positive (as well as m _(S) and m _(H)) in the dissolution of non-polar substances, whereas it is negative (as well as m _(S) and m _(H)) in bio-complex formation and in micelle formation. The number n _w (n _w>0) involved in the dissolution of non-polar substances depends on the size of the cavity (excluded volume) formed in the structure of water. These water molecules that have been excluded from the structure of the solvent absorb thermal energy that compensates for the negative enthalpy change, whereas the formation of the cavity implies there should be a large negative entropy contribution. The low solubility of non-polar substances in water depends on the highly negative entropy effect due both to cavity formation and to loss of configurational entropy by the gas trapped in a cage of water molecules. In processes involving association, as in micelle formation and in protein complexation, the cavities surrounding the separate units coalesce and the resultant cavity is smaller than the sum of the previous ones. The n _w water molecules (n _w<0) needed to fill the excess cavity return to the structure of the bulk solvent and release thermal energy, which compensates for the endothermic enthalpy. The affinity in the association processes is bound, for the most part, to the entropy produced by occupation of part of the cavity by condensation of water molecules. The association processes are therefore entropy driven.     

Zirconium Dioxide Solubility in High Temperature Aqueous Solutions

The heat transport purification system of CANDU nuclear reactors is used to remove particulates and dissolved impurities from the heat transport coolant. Zirconium dioxide shows some potential as a high-temperature ion-exchange medium for cationic and anionic impurities found in the CANDU heat transport system (HTS). Zirconium in the reactor core can be neutron activated, and potentially can be dissolved and transported to out-of-core locations in the HTS. However, the solubility of zirconium dioxide in high-temperature aqueous solutions has rarely been reported. This paper reports the solubility of zirconium dioxide in 10⁻⁴ mol⋅kg⁻¹ LiOH solution, determined between 298 and 573 K, using a static autoclave. Over this temperature range, the measured solubility of zirconium dioxide is between 0.9 and 12×10⁻⁸ mol⋅kg⁻¹, with a minimum solubility around 523 K. This low solubility suggests that its use as a high-temperature ion-exchanger would not introduce significant concentrations of contaminants into the system. A thermodynamic analysis of the solubility data suggests that Zr(OH)₄⁰ likely is the dominant species over a wide pH region at elevated temperatures. The calculated Gibbs energies of formation of Zr(OH)₄⁰(aq) and Zr(OH)₄(am) at 298.15 K are −1472.6 kJ⋅mol⁻¹ and −1514.2 kJ⋅mol⁻¹, respectively. The enthalpy of formation of Zr(OH)₄⁰ has a value of −1695±11 kJ⋅mol⁻¹ at 298.15 K.     

Temperature Dependences of HCl Activity Coefficients in Aqueous Solutions

Temperature coefficients of activity of the ionic fraction of HCl in water, calculated from tensimetric and calorimetric data, are compared. A correlation dependence is suggested for recalculating the activity coefficients of hydrochloric acid from 298 K to other temperatures.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 2, 2005, pp. 211–213.Original Russian Text Copyright © 2005 by Poltoratskii, Osovskaya, Chumanov.     

高温水溶液pH值原位测量系统与机理

研制了以氧化钇稳定氧化锆(YSZ)陶瓷薄膜电极为pH电极、外置压力平衡式Ag/AgCl电极为参比电极的高温高压水溶液pH值原位测量系统,测量了H₃BO₃\LiOH水溶液在473.15~573.15 K范围内的pH值,并与热力学计算得到的pH值比较。 结果表明,当温度高于548.15 K时,测量系统可以实现pH值的准确测量;而低于此温度时,由于YSZ陶瓷膜内阻过大,测得的pH值与理论计算值存在偏差,且随温度的降低,测量偏差增大。 讨论了该系统的pH值测量机理。     

Color Removal from Aqueous Solutions of Humic Substances in the Presence of Praestol and Aluminum Sulfate

Color removal from aqueous solutions of humic substances by introducing Praestol (cationic coagulant) in combination with aluminum sulfate (flocculant) was studied as a function of the coagulant and flocculant concentrations, chemical composition of flocculant, its molecular weight, macromolecule conformation in solutions, pH, and the order and time of coagulant and flocculant introduction.     

Cationic and Anionic Effects on the Glass Transition Temperature for Aqueous Electrolyte Solutions

Glass-forming composition regions of aqueous CH₃COOM (M = Li, Na, K, Rb, Cs, and Tl), CF₃COOM (M = Li, Na, K, Rb, and Cs), and Et₄NX (Et₄ = C₂H₅, X = OH, CH₃COO, Cl, Br, NO₃, and SCN) solutions are reported as a function of water concentration R (R = moles of water per moles of salt). Glass transition temperatures (T _g) were measured by a simple differential thermal analysis (DTA) method with a cooling rate of about 600 K-min^–1. The T _g of all solutions decrease with increasing R (decreasing salt concentration). It is found that T _g at the same R value decrease in the order Na⁺ > Li⁺ > K⁺ > Rb⁺ > Cs⁺ in all glass-forming composition regions of the alkali acetate salt and alkali trifluoroacetate salt solutions. T _g for Et₄NX solutions decrease in the order CH₃COO^– ~OH^– > Cl^– > Br^– > NO ₃ ^– > SCN^–. The effects of the cation and anion on the glass-forming behavior in these aqueous solutions are discussed.     

Electrolytic Deposition of Molybdenum Oxide from Aqueous Solutions at Room Temperature

The conditions of electrolytic deposition of molybdenum oxide from aqueous solutions at room temperature were studied and the optimal parameters of electrolysis, which provide deposits with necessary physical and structural characteristics, were chosen.     

A New Predictive Equation for the Depression in Freezing Points of Multicomponent Aqueous Solutions Conforming to the Linear Isopiestic Relation

The linear isopiestic relation has been used together with a well-known thermodynamic equation to establish a new predictive equation for freezing point depression. This equation can provide predictions for multicomponent solutions conforming to the linear isopiestic relation using only information on the corresponding binary subsystems. The predictive capability of the equation has been tested by comparing with the experimental data at 25°C reported in the literature and particularly those of Pathwardhan and Kumar. The systems used are NaCl—MgCl₂—H₂O, NaCl—BaCl₂—H₂O, NaCl—CaCl₂—H₂O, LiCl—NaCl—H₂O, LiCl—KCl—H₂O, LiCl—CsCl—H₂O, NaCl—KCl—H₂O, and NaBr—KBr—H₂O. The predictions of the two equations agree well with the experimental data although our new equation is, in general, better.     

Predicting Toxicity Parameters of Harmful Substances for Hydrobionts

Russian Journal of General Chemistry - The author?s procedure for predicting toxicity parameters of various harmful substances for hydrobionts (daphnia, infusoria) over a wide range of...     

Effect of Temperature on Micelle Formation in Aqueous NaBr Solutions of Octyltrimethylammonium Bromide

Association processes in aqueous solutions of octyltrimethylammonium bromide, C(8)TAB, have been studied in aqueous NaBr solutions at temperatures from 20 to 55 degrees C. The values of the critical micelle concentration, CMC, were determined from the intersections of two straight line portions of the plots of the relationship between adiabatic compressibility of the solutions and surfactant concentration. The value of the CMC thus determined exhibits minima at a certain temperature, T(min). The value of T(min) shifts toward a lower temperature with increasing NaBr concentration. Based on the most probable micelle size model, the values of thermodynamic functions of micelle formation have been estimated at various temperatures. Copyright 2001 Academic Press.     

Enthalpies of Dilution for Aqueous Solutions of 3:1 Electrolytes: Variation with Temperature

The enthalpies of dilution of aqueous solutions of [Co(en)₃]Cl₃ and [Co(tn)₃Cl₃ (where en=1,2-diaminoethane, and tn=1,3-diaminopropane) were measured at 278.15 K up to 1 mol kg^-1, using a large isoperibolic calorimeter, with the 'long-jump' method. Relative apparent molar enthalpies, L_Φ>, were extracted via an empirical equation relating L_Φ> and molality. These new values were compared with previous results at 298.15 K on the same aqueous systems. Theoretical predictions were satisfied, but an unexpectedly broad divergence was found for such close temperatures. A tentative explanation is put forward. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Separation of Nonvolatile Substances by Means of Compressed Gases in Countercurrent Processes

Mixtures of nonvolatile and heat-sensitive substances can be separated by means of compressed gases in countercurrent processes. Moreover, such separations can be carried out at lower temperatures than in vacuum distillation. Addition of an entrainer enables alteration of the relative volatilities of the components. That such a method of separation is feasible on a large scale is illustrated using as example the separation of monoglycerides from a mixture of oleic glycerides at e.g. 110°C/135 bar. Propane is used as compressed gas, and acetone as entrainer.     

Numerically Calculating the Concentration and Temperature Dependences of the Electrical Conductivity of Aqueous Electrolyte Solutions

Russian Journal of Physical Chemistry A - Kinetic equations are used to find analytical expressions for dynamic electrical conductivity $$sigma (omega )$$ and electroelasticity modulus $$ {in}...