Function Of Molality Research Articles

Volumetric properties of (ascorbic acid + polyethylene glycol 3350 + water) systems at T = (288.15, 298.15, and 308.15) K

Density and ultrasound speed were measured accurately for binary ascorbic acid–water and ternary ascorbic acid–water–polyethylene glycol 3350 (PEG3350) solutions at T = (288.15, 298.15, and 308.15) K. The data were used to evaluate thermodynamic properties as apparent molar volumes, V ϕ , and apparent molar isentropic compressions, K S Φ , of ascorbic acid in water and in aqueous PEG3350 solutions. Infinite dilution values of these parameters, V ϕ ∘ and K S Φ ∘ , were obtained from their plots as a function of molality and have been utilized in obtaining transfer volumes and transfer compressions of ascorbic acid from water to PEG3350 solutions at various weight percentages. All transfer volumes and compressions at infinite dilution were found to be positive, to increase with weight per cent of PEG3350 and to decrease with temperature. Apparent molar isobaric expansions at infinite dilution were derived from the temperature dependence of V ϕ ∘ values. The results were interpreted in terms of ascorbic acid–water–PEG3350 interactions.

Ultrasonic Velocity and Density Studies of Solutions of Maleic Acid and Tartaric Acid in Water at T = (298.15 and 308.15) K

Ultrasonic-velocity and density measurements of aqueous solutions of maleic acid and tartaric acid have been made as a function of molality, at T = (298.15 and 308.15) K, and at atmospheric pressure. A molality range has been studied from (0.2603 to 2.6309) mol·kg−1 and (0.4451 to 2.6621) mol·kg−1 for maleic and tartaric acids, respectively. The experimental data have been correlated with molality using a polynomial equation. Furthermore, apparent molar volume, partial molar volume, apparent-specific molar volume, isentropic compressibility, apparent molar isentropic compressibility, limiting apparent molar isentropic compressibility, and isentropic apparent-specific compressibility values have been calculated from experimental values of densities and ultrasonic velocities. The calculated parameters have been interpreted in terms of solute–solvent interactions, solute–solute interactions, structure making/breaking behavior of acids, and their taste quality in water.

Temperature dependence of micellar sphere-to-rod transition using adiabatic compressibility

Temperature dependence of critical micelle concentration as well as the sphere-to-rod critical micelle transition has been studied by using densitometry and sound velocity determinations as a function of molality. In order to understand the properties of the globular micelles the apparent molar quantities like the volume and adiabatic compressibility have been determined and discussed in comparison with the corresponding spherical micelles. An inverted U-shape for the sphere-to-rod transition was obtained.

Interactions of polyethylene glycols with water studied by measurements of density and sound velocity

Densities and sound velocities of ethylene glycol (EG) and polyethylene glycols (PEGs) of molecular weight 200, 300, 400, 550, 600, 1000, 1450, 3350, 8000, and 10,000 at (288.15, 298.15, and 308.15) K were measured with high precision vibrating tube densimeter and sound velocity measuring device. They were used to evaluate apparent molar volumes, V ∅, and apparent molar isentropic compressibilities, K ΦS . Infinite dilution values of these parameters, V ∅ ∘ , and K Φ S ∘ , were obtained from their plot as a function of molality. The variations of V ∅ ∘ , and K Φ S ∘ , with the number of repeating units in PEGs and with temperature were examined. Comparison of the experimentally obtained data was made with the available literature data and also with some values predicted according to group additivity approach. The results were interpreted in terms of hydration and conformational effects of PEGs in water. A correlation was also examined between V ∅ ∘ or K Φ S ∘ values of PEGs in water and equilibrium moisture contents of PEGs as well as the water vapor permeabilities (WVP) of edible films containing PEGs.

Solid–Liquid Equilibrium of Maltitol Aqueous Solutions—Implications on the Crystallization Behavior and Process

The solubility of maltitol in pure water and industrial syrup was measured in a temperature range from 10 to 90 °C. Maltitol is highly soluble in water, and this yields high viscosity values for the saturated aqueous solutions at different temperatures. In addition, solubility of maltitol in ethanol/water mixtures was followed at 30, 35, 45, and 55 °C. Results show that maltitol solubility is highly dependent on water content in the solvent mixture. Moreover, it increases monotonically with temperature. The logarithm of viscosity changes linearly against the mole fraction of maltitol in the aqueous solutions up to saturation. The saturated solutions showed a Newtonian behavior in a temperature range from 20 to 90 °C. Maltitol is also characterized in supersaturated solutions by a narrow metastable zone, which slightly increases as temperature is raised. The density of aqueous solutions of maltitol was measured as a function of molality up to saturation at 20 °C, and results show that density can be correlated with concentration according to a linear relation. The obtained results were used to explain maltitol crystallization, which exhibits a high nucleation rate and a slow growth leading to small size crystals.

Densities and apparent molar volumes of oxalic acid in water and in aqueous solutions of sucrose at 293.15, 303.15, 313.15 and 323.15 K

Apparent molar volumes (V Φ ) of oxalic acid in water and in aqueous sucrose solutions with concentrations ≈(0.5-2.0) mol kg -1 have been determined as a function of molality by measuring the densities at 293.15, 303.15, 313.15 and 323.15 K. From these data the limiting apparent molar volume (V 0 Φ ), which is equal to the partial molar volume at infinite dilution (V 0 2 ), has been obtained at different temperatures. The partial molar volumes have been used to calculate the partial molar volumes of transfer (ΔV 0 Φ ) of oxalic acid from water to aqueous sucrose solutions. The values of limiting apparent molar expansibilities, (Φ 0 E ) and that of (∂ 2 V 0 Φ /∂T 2 ) p have also been determined from temperature-dependence of V 0 Φ at various concentrations of the sucrose solutions. The results have been discussed in terms of various interactions operating in oxalic acid, water and sucrose systems.

The dissociation of carbonic acid in NaCl solutions as a function of concentration and temperature

Potentiometric measurements of the stoichiometric constants for the dissociation of carbonic acid in NaCl solutions ( K 1 ∗ = [ H + ] [ HCO 3 - ] / [ CO 2 ] and K 1 ∗ = [ H + ] [ CO 3 2 - ] / [ HCO 3 - ] ) have been made as a function of molality (0–6 m) and temperature (0–50 °C). The results have been fitted to the equations p K i ∗ - p K i = A i + B i / T + C i ln T The values of p K i in pure water are taken from the literature and the adjustable parameters A i , B i and C i are a function of molality A 1 = 35.2911 m 0.5 + 0.8491 m - 0.32 m 1.5 + 0.055 m 2 B 1 = - 1583.09 m 0.5 C 1 = - 5.4366 m 0.5 A 2 = 38.2746 m 0.5 + 1.6057 m - 0.647 m 1.5 + 0.113 m 2 B 2 = - 1738.16 m 0.5 C 2 = - 6.0346 m 0.5 ( σ = 0.013 for p K 1 ∗ and σ = 0.020 for p K 2 ∗ , N = 603). The values determined in this study are in good agreement with the 25 °C literature values. Our results have been combined with previous measurements to derive equations that are valid from 0 to 250 °C and 0 to 5 m. This large data set has been used to determine the Pitzer parameters ( β (0), β (1) and C ϕ ) for the interactions of Na + with HCO 3 − and CO 3 2− from 0 to 250 °C. These results extend the carbonate system Pitzer model to hydrothermal brines containing high concentrations of NaCl.

Hygroscopic growth and critical supersaturations for mixed aerosol particles of inorganic and organic compounds of atmospheric relevance

Abstract. The organic fraction of atmospheric aerosols contains a multitude of compounds and usually only a small fraction can be identified and quantified. However, a limited number of representative organic compounds can be used to describe the water-soluble organic fraction. In this work, initiated within the EU 5FP project SMOCC, four mixtures containing various amounts of inorganic salts (ammonium sulfate, ammonium nitrate, and sodium chloride) and three model organic compounds (levoglucosan, succinic acid and fulvic acid) were studied. The interaction between water vapor and aerosol particles was studied at different relative humidities: at subsaturation using a hygroscopic tandem differential mobility analyzer (H-TDMA) and at supersaturation using a cloud condensation nuclei spectrometer (CCN spectrometer). Surface tensions as a function of carbon concentrations were measured using a bubble tensiometer. Parameterizations of water activity as a function of molality, based on hygroscopic growth, are given for the pure organic compounds and for the mixtures, indicating van't Hoff factors around 1 for the organics. The Zdanovskii-Stokes-Robinson (ZSR) mixing rule was tested on the hygroscopic growth of the mixtures and it was found to adequately explain the hygroscopic growth for 3 out of 4 mixtures, when the limited solubility of succinic acid is taken into account. One mixture containing sodium chloride was studied and showed a pronounced deviation from the ZSR mixing rule. Critical supersaturations calculated using the parameterizations of water activity and the measured surface tensions were compared with those determined experimentally.

Isentropic Compressibility, Shear Relaxation Time, and Raman Spectra of Aqueous Calcium Nitrate and Cadmium Nitrate Solutions

Speed of sound, viscosity and Raman spectra of aqueous calcium nitrate and cadmium nitrate solutions were measured as functions of molality and temperature. The isentropic compressibility isotherms for both systems cross over in a narrow molality region. In comparison with Ca(NO3)2(aq) solutions, Cd(NO3)2(aq) solutions have lower isentropic compressibilities due to a lower charge to radius ratio. The observed Raman spectral changes in the ν3 (≈1400 cm−1) and ν4 (≈700 cm−1) modes with an increase in molality suggest that the symmetry of NO3− changes from D3h to C2v, and solvent-separated and/or solvent-shared ion pairs are formed in both systems. The results from plotting electrical conductivity versus shear relaxation time also imply that the influence of the solvent-separated and/or solvent-shared ion pairs begins ≈2.0 mol-kg−1 for these systems. The larger Δν values for the ν3 mode for Cd(NO3)2(aq) solutions indicate stronger solvent-separated and/or solvent-shared ion pairs formation in comparison to Ca(NO3)2(aq) solutions.

Temperature dependence of second critical micelle concentration of dodecyldimethylbenzylammonium bromide in aqueous solution

The specific conductivity of dodecyldimethylbenzylammonium bromide (C12BBr) in aqueous solutions, in the temperature range of 15 to 40 °C, has been measured as a function of molality. The two breaks which were found on the conductivity against molality plots were attributed to the critical micelle concentration, cmc, and second critical micelle concentration, 2nd cmc, respectively. The ratio of the slopes, S, of the three linear fragments on the plots, S2/S1 and S3/S1, was attributed to the degree of ionization of the micelles at cmc and 2nd cmc respectively. It was shown that the values of the 2nd cmc estimated above 27 °C are only apparent due to thermal disintegration of the micelles. In the temperature range of 15 to 27 °C, the values of the 2nd cmc increase gradually and the plot of the 2nd cmc against temperature is concave. The ratio of 2nd cmc/cmc for C12BBr at 25 °C amounts to 15 and appears to be high compared to the literature values for other surfactants. For comparative purposes the cmc and 2nd cmc values were also estimated conductometrically for decyldimethylbenzylammonium bromide (C10BBr) at 25 °C. The 2nd cmc value for this surfactant is higher compared to the value for the C12 homologue by a factor of 2.6.The standard Gibbs free energies of micellization at cmc and at the 2nd cmc were estimated from the experimental data for both surfactants at 25 °C.

Thermodynamics of micellization of decyldimethylbenzylammonium bromide in aqueous solution

Abstract The specific conductivity, κ, of decyldimethylbenzylammonium bromide (C10BBr) in aqueous solution was measured as a function of molality in the 5–50 °C temperature range at 1 °C intervals. The κη against temperature plots (where η is the viscosity of water at the corresponding temperature) exhibit three, molality dependent regions. In the premicellar concentration range the plots are linear with a small negative slope. A concavity on the plots, due to change in the degree of ionization of the micelles and the U-shaped dependence of the critical micelle concentration, cmc, on temperature, is observed in the immediate post-micellar concentration range. At high concentration of the surfactant a monotonic increase of the slope of the plots can be observed. The critical micelle concentration, cmc, of C10BBr and ionization degree of the micelles, β, were estimated from the intersection of two extrapolated linear fragments of the conductivity against molality plots and the ratio of the slopes of the two lines, respectively. Comparison with literature data indicates that the minimum on the cmc against temperature plots, T*, is shifted to lower temperatures with increase in length of the alkyl chain of the surfactant and with increase in hydrophobicity of the counterion. The temperature dependence of ln χcmc (χcmc being the cmc expressed as mol fractions) was fitted to an equation suggested by Muller, which was modified by taking into account the temperature dependencies of both of β and of change in heat capacity upon micellization. From the fitting parameters, Gibbs free energies, enthalpies and entropies of micellization of C10BBr as a function of temperature were estimated. Enthalpies and entropies were found to be strongly correlated.

Thermodynamics of Micellization of Alkyldimethylbenzylammonium Chlorides in Aqueous Solutions

Specific conductivities of alkyldimethylbenzylammonium chlorides (alkyl=decyl-, dodecyl-, tetradecyl-, and hexadecyl-) in aqueous solutions were measured as a function of molality and temperature. Critical micelle molalities (cmc) and degrees of ionization of the micelles, β, were estimated from the dependence of the specific conductivity on molality. It was found that temperature dependence of cmc is U-shaped with a minimum shifting toward higher temperatures with a decrease in the chain length of the alkyl group. The temperature dependence of ln xcmc (where xcmc is the cmc in mole fraction units) was fitted to the equation of Muller, which we modified by taking into account the temperature dependencies both of β and of change in heat capacity upon micellization. From the fitting parameters, Gibbs free energies, enthalpies, and entropies of micellization as a function of temperature were estimated.

Thermodynamic Properties of the KCl+H2O System

The thermodynamic properties of the KCl+H2O system were examined in order to provide: (1) an improved equation for the osmotic coefficient as a function of molality and temperature for purposes of isopiestic measurements, (2) a determination of the thermodynamic properties of the standard-state solution process, and (3) a test of the accuracy of the enthalpy of solution values for KCl(cr), a calorimetric standard. New equations that describe the thermodynamic properties of the KCl+H2O system were obtained from previously published measurements for this system. The measured values included in the fitted equations spanned the range of temperature from approximately 260 to 420 K for KCl(aq) and 1.5 K to 1033.7 K for KCl(cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of KCl(cr) from 0 K to the melting point, 1045 K, (2) the change in chemical potential for both KCl and H2O in KCl(aq) as a function of temperature, and molality, valid from 260 to 420 K, and (3) standard-state properties for the aqueous solution process. The effect of heat treatment on the determination of enthalpy of solution values was also examined. This examination indicated that the NIST recommendation of heating Standard Reference Material 1655, potassium chloride, at 800 K for a minimum of 4 h prior to its use in calorimeter calibration, should probably not be followed. The heat treatment recommended by the NIST certificate appears, at this point, to have a higher probability of corrupting the sample than improving the accuracy of the measurement.

Improved apparatus and procedures for isopiestic studies at elevated temperatures

A significantly improved apparatus for the isopiestic measurement of thermodynamic activities at elevated temperatures is described. Details of the new design and of an analysis of the propagation of the experimental errors are presented. The apparatus was tested by measurements of calcium chloride against sodium chloride at 353.15 K. Accuracies of better than 0.1% in the osmotic coefficient are routinely achieved. Data are also given for the osmotic coefficient of aqueous sodium hydroxide solutions at 353.15 K as a function of molality (up to 13 mol/kg), measured with respect to both sodium chloride and calcium chloride solutions as reference electrolytes.

Thermodynamic properties of aqueous 1-n-alkanepyridinium chlorides at temperatures from 283.15 K to 343.15 K

Osmotic coefficients φ of aqueous solutions of 1-n-decanepyridinium chloride, 1-n-dodecanepyridinium chloride, and 1-n-hexadecanepyridinium chloride are estimated atT=328.15 K from vapor pressure osmometric measurements. Molar integral enthalpies of dilution ΔdilHmhave been measured for aqueous solutions of these surfactants, and also for aqueous solutions of 1-n-tetradecanepyridinium chloride, atT=(283.15, 298.15, 313.15, 328.15, and 343.15) K. Measurements were made, where possible, at molalities from well below to well above the critical micelle molalitym(cmc). Values of φ and ΔdilHmfor each surfactant were treated using a mass-action model that includes ion-interaction term for the activity coefficients of both micellar and monomeric ionic species in solution. The ion–ion interaction parameters were estimated from values of φ reported in this investigation and from values reported in the literature. The temperature coefficients of these parameters were estimated from values of ΔdilHm. Treatment of ΔdilHmwith the model also leads to values of ΔrH°mfor the reaction of monomeric surfactant and Cl−(aq) to form micelles, and to the corresponding values valid at finite molalities, includingm(cmc). Fitting all values of ΔdilHmsimultaneously for a surfactant yields numerical values of a small number of parameters for equations that represent its behavior in terms of an equilibrium constant, an activity coefficient equation, and their temperature derivatives. Systematic trends in measured properties and derived parameters as functions of molality, temperature, and surfactant structure are discussed briefly.

Thermodynamic Study of Aqueous Micellar Solutions of Biologically Active Bisquaternary Ammonium Chlorides

Thermodynamic properties of aqueous solution of bisquaternary ammonium salts, which are derivatives ofN,N-bisdimethyl-1,2-ethanediamine (bis-Cn-BEC), of general formula/CnH2n+1OOCCH2(CH3)2N[formula]CH2CH2N[formula](CH3)2CH2COOCn-H2n+1/2Cl−(bis-Cn-BEC, where the subscriptnstands for the number of carbon atoms of the alkyl chain bound to the carboxyl group) are here reported and compared with those of the corresponding monomers. Dilution enthalpies have been measured by means of a flow type microcalorimeter at 313 K, and densities have been measured by means of a vibrating tube densimeter at 298 K. Apparent and partial molar quantities have been obtained from the experimental data and expressed as a function of molalities, assuming the infinite dilution as standard state. The changes in enthalpy and in volume upon micellization have been evaluated by assuming the pseudo-phase transition model. From the calculated enthalpy changes at 313 K and that previously reported at 298 K, the changes in heat capacity for micellization has been evaluated. The data suggest the hypothesis that the alkyl chain in the dimers are already partially associated in solution. Moreover, the trends of the cmc as a function of the chain length for monomers and dimers suggest that the association of the chains probably leaves out the first three methylene groups of the alkyl chains bound to the carboxylic groups. The packing parameter,P, gives 0.37 for bis-C10-BEC, and the formation of rod-like micelles is therefore suggested.

Thermodynamics of aqueous micellar solutions of selected permeatoxins at 298.15 and 313.15 K

Thermodynamic properties of aqueous solutions of N-dodecyl- N-ethylpiperidinium chloride (DMePC) and N-dodecyloxymethylene- N-methylpiperidinium chloride (DOMePC) at 298.15 and 313.15 K are reported for the first time. These compounds show biological activity and influence ion transport through membranes. Apparent and partial molar enthalpies and volumes have been obtained from the experimental data and expressed as a function of molalities, assuming infinite dilution as the standard state. The critical micelle concentrations at 313.15 K have been obtained from osmotic measurements, allowing also the evaluation of solution non-ideal free energies and entropies. The changes in thermodynamic properties for the micellization process have been derived, assuming a pseudo phase transition approach. The trends of the enthalpic curves of DMePC with DOMePC and also of DMePC with those of N-dodecyl- N-methylmorpholinium chloride (DMeMC) previously reported have been compared. It has been stated that the substitution of a methylene group by an oxygen atom, either in the polar part of an amphiphile or in its chain in the vicinity of the polar head group, has a small effect on the thermodynamic properties and micellization process of the amphiphile. A similar effect was also observed in the case of substitution of the first two methylene groups of n-alkyltrimethylammonium chlorides by the CH 2COO group. The above behaviour is explained as the result of micelle hydration at the depth of the first two methylene groups.

The Use of Freezing‐Point Depression for the Theoretical Dextrose Equivalent Measurement

AbstractThe determination of the theoretical dextrose equivalent was investigated, by measuring the osmolality (mol dissolved particles/kg H2O) by freezing‐point depression. Relations for dextrose equivalent and increase in dry weight during a hydrolysis were derived as a function of molality and amount of dry weight at the start of the hydrolysis. With freezing‐point depression it was possible to determine the theoretical dextrose equivalent of oligosaccharides (dextrose to maltoheptaose), whereas a traditional titration method (Luff‐Schoorl) overestimates 20‐50%. The relation for the increase of dry weight during the hydrolysis of starch with an α‐amylase was experimentally validated. The overestimation of dextrose equivalent by Luff‐Schoorl titration was also evident in the hydrolysis of amylopectin potato starch. With freezing‐point depression it was possible to determine the theoretical dextrose equivalent fast and accurate.

Differential enthalpies of solution of LiCl·H2O, NaCl, KCl, MgCl2·6H2O, CaCl2·6H2O, and BaCl2·2H2O in water at 298.15 K, near the saturation concentration

The direct measurements of differential enthalpies of solution Δsol H 2, of LiCl·H2O, NaCl, KCl, MgCl2·6H2O, CaCl2·6H2O and BaCl2·2H2O, as the function of molality,m, in the region of concentrated solutions were performed. On this basis the enthalpies of crystallization, Δcryst H m, were calculated and compared to the appropriate literature data.

Low Electrolytic Conductivity Standards.

Standards of low electrolytic conductivity were developed to satisfy the demands of the U.S. Navy and American industry for the measurement of high quality water. The criteria for the selection of appropriate solvent and solutes, based on the principles of equivalent conductivity and Onsager’s limiting law, are described. Dilute solutions of potassium chloride and benzoic acid in 30 % n-propanol–water have been chosen as standards. The electrolytic conductivity of both sets of these solutions as a function of molality was determined. Solutions of potassium chloride and of benzoic acid are recommended for use as 5 μS/cm, 10 μS/cm, 15 μS/cm, 20 μS/cm, and 25 μS/cm conductivity standards. Solutions prepared from potassium chloride in 30 % n-propanol–water have been certified as Standard Reference Materials (SRMs). SRM 3198 and SRM 3199 are certified nominally at 5 μS/cm and 15 μS/cm, respectively, at 25.000 °C.