Ângela F. S. S. Mendonça

Volumetric properties of 2-ethylaminoethanol in water from 283.15 to 303.15 K

Accurate density values, at ambient pressure, were obtained in aqueous binary mixtures of 2-ethylaminoethanol (EEA) over the whole composition range at intervals of 5 K in the temperature range between 283.15 and 303.15 K. To gain some insight into the several aggregation patterns present in these mixtures, calculation of excess molar volumes of the mixture, apparent molar and excess partial molar volumes of both components were made over the entire composition and temperature ranges. Thermal expansibility effects on this amphiphile/water mixture are analysed in terms of excess molar isobaric expansions EEP,m for the mixture and of excess apparent molar isobaric expansions EEP,φ,i for both chemical substances in the mixture. Limiting excess partial molar isobaric expansions have been calculated as well, from the temperature dependence of limiting excess partial molar volumes. An analytical method based on Redlich–Kister fitting equations for VEm as a function of the mole fraction, has been used to obtain VE,∞i. The excess properties are referred to a thermodynamically defined ideal liquid mixture. Interesting insights into the mixing process are gained from the visual impact of plots showing the composition and temperature dependence of different excess molar thermodynamic properties.

Isobaric expansions and isentropic compressions of aqueous binary mixtures of 2-diethylaminoethanol from 283 to 303 K

Densities and ultrasound speeds were determined in aqueous binary mixtures of 2-diethylaminoethanol over the whole composition range at intervals of 5 K in the temperature range between 283 and 303 K. Thermal expansibility effects on this amphiphile/water mixture are analysed in terms of excess molar isobaric expansions EEP,m for the mixture and of excess apparent molar isobaric expansions EEP,ϕ,i for both chemical substances in the mixture. Different strategies are used and discussed for obtaining limiting (infinite dilution) excess partial molar isobaric expansions. Compressibility effects are described in terms of excess molar isentropic compressions KES,m and excess partial molar isentropic compressions KES,i. The latter properties are analytically calculated from the fit of experimental KES,m data to a Redlich–Kister equation. A method based on this equation yields limiting excess partial molar isentropic compressions. Additionally, excess ultrasound speeds uE are also examined. All these excess properties are referred to a thermodynamically defined ideal liquid mixture. Interesting insights into the mixing process are gained from the visual impact of plots showing the composition and temperature dependence of different excess molar thermodynamic properties. Comparison of expansibility- and compressibility-related quantities shows that these two types of thermodynamic properties probe different aspects of intermolecular and packing effects on the process of mixing amphiphiles and water.

Uncertainties of useful thermodynamic properties calculated from ultrasound speed measurements in liquids and solutions

Calibration of a modified sing-around ultrasound velocimeter, with ultra-pure water, has been done using sound speed data recommended in the literature for pure water. Empirical calibration parameters were evaluated by a least-squares fitting method and the impact of both the uncertainties in measured quantities and propagation of uncertainties in the calibration parameters and other influence quantities on uncertainties in the calculated sound speed in water have been estimated. Examples are given for calculating the uncertainties of some useful thermodynamic properties derived from ultrasound speed data that are used in important industrial applications such as estimating concentration of solutions and density of binary liquid mixtures.

Solubility of Triethylamine in Tetraethylammonium Chloride Aqueous Solutions from 20 to 35°C

Solubilities of triethylamine in aqueous tetraethylammonium chloride solutions were measured at 20, 25, and 35°C. The molalities in Et4NCl of the aqueous solvents ranged from 0.03 to 1 mol-kg−1. The data were evaluated from density measurements using a vibrating-tube densimeter. At each temperature, least-squares method was used to fit experimental density data points to double polynomial equations of various degrees. Triethylamine molalities of the saturated aqueous phases were estimated by extrapolation from those equations. Experimental data were interpreted in terms of hydrophobic and electrostatic perturbed domains in the hydration shells of the noneleceory and of the cation of the salt, as a function of temperature and salt concentration. The conclusions obtained are consistent with previous volumetric studies.