Ethanol-water mixtures, properties

Cohn, E.J. et al. (1947) Preparation and properties of serum and plasma proteins. XIII. Crystallization of serum albumins from ethanol-water mixtures./. Am. Chem. Soc. 69, 1753-1761. 

The state function property of the enthalpy should be kept in mind for the next move of our discussion. In figure 2.1 we have decomposed reaction 2.1 in a series of steps whose net effect must correspond to the overall reaction. This means that the correct value for Asin//(2) is the solution enthalpy of 1 mol of oxygen in the (ethanol + water) mixture described—and not the solution enthalpy of the gas in pure water. Unfortunately, solution enthalpy data in organic liquid mixtures are not abundant in the chemical literature. So, either we are lucky to find them, we have the equipment to measure them in the laboratory, or we assume that the values will be identical to the ones in the pure solvent. The validity of this assumption depends on the system under discussion and on the accuracy needed for the final result, but in the present case it seems fair. Leaving further discussion to section 2.5, we shall take Asin//(2) = -12 4 kJ mol-1 [17],... 

The salt effects of potassium bromide and a series office symmetrical tetraalkylammonium bromides on vapor-liquid equilibrium at constant pressure in various ethanol-water mixtures were determined. For these systems, the composition of the binary solvent was held constant while the dependence of the equilibrium vapor composition on salt concentration was investigated these studies were done at various fixed compositions of the mixed solvent. Good agreement with the equation of Furter and Johnson was observed for the salts exhibiting either mainly electrostrictive or mainly hydrophobic behavior however, the correlation was unsatisfactory in the case of the one salt (tetraethylammonium bromide) where these two types of solute-solvent interactions were in close competition. The transition from salting out of the ethanol to salting in, observed as the tetraalkylammonium salt series is ascended, was interpreted in terms of the solute-solvent interactions as related to physical properties of the system components, particularly solubilities and surface tensions. 

A test set of 6 to 13 aroma compound partition coefficients between different food contact polymers (low density polyethylene (LDPE), high density polyethylene (HDPE) polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA)) and different food simulant phases (water, ethanol, aqueous ethanol/water mixtures, methanol, 1-propanol) were taken from the literature (Koszinowski and Piringer, 1989, Baner, 1992, Franz, 1990, Koszinowski, 1986, Franz, 1991, Baner, 1993, Piringer, 1992). Table 4-2 shows the test set of 13 different aroma compounds, with their properties and their structures. The experimental data were compared to estimations using different estimation methods of UNIFAC-FV, GCFLORY (1990), GCFLORY (1994) and ELBRO-FV. 

The giant clusters could be reproducibly formed starting from Pd561 nanocrystals in water, ethanol and ethanol-water mixtures and from sols with very different concentrations of the nanocrystals. It is possible that the formation of the giant clusters is facilitated by the polymer shell that encases them. Unlike Pd nanocrystals coated with alkanethiols, which self-assemble to form ordered arrays, the polymer shell effectively magnifies the facets of the metallic core, thereby aiding a giant assembly of the nanocrystals. The surface properties of the polymer-coated nanocrystals are clearly more favorable in that the interparticle interaction becomes sufficiently attractive. 

The high solubility and high stability of substituted polyacetylenes are the two most important properties which are not seen with polyacetylene. Consequently, stable membranes can be easily obtained by casting solutions of substituted polyacetylenes. This will greatly facilitate their application. Here, we refer to several functions of substituted polyacetylenes, which might be applied to oxygen enrichment of air, separation of ethanol-water mixtures, and so on. 

They are used as industrial solvents for small- and large-scale separation processes, and they have unusual thermodynamic properties, which depend in a complicated manner on composition, pressure, and temperature for example, the excess molar enthalpy (fp-) of ethanol + water mixture against concentration exhibits three extrema in its dependence on composition at 333.15 K and 0.4 MPa. The thermodynamic behavior of these systems is particularly intricate in the water-rich region, as illustrated by the dependencies of the molar heat capacity and partial molar volume on composition. This sensitivity of the partial molar properties indicates that structural changes occur in the water-rich region of these mixtures. Of course, the unique structural properties of water are responsible for this behavior. ... 

A partial molar property of a component in a mixture may be either greater than or less than the corresponding pure-component molar property. Furthermore, the partial molar property may vary with composidon in a complicated way. Show this to be the case by computing (a) the partial molar volumes and (b) the partial molar enthalpies of ethanol and water in an ethanol-water mixture. (The data that follow are from Volumes 3 and 5 of the International Critical Tables, McGraw-Hill, New York, 1929.)... 

Figure 5.4 shows how temperature affects the excess properties in ethanol-water mixtures. At ambient temperatures, and are negative, with Ts < h, so g is positive. As T increases, both and become more positive. Note that at 70°C, may be positive or negative, depending on composition. These changes in excess properties reflect complex and subtle changes in effects of molecular interactions in response to the change in temperature. 

The behavior of the excess properties for ethanol-water mixtures, shown in Figure 5.4, suggests that modeling excess properties can be difficult. 

Zhang, C. and Yang, X. (2005). Molecular dynamics simulation of ethanol/water mixtures for structure and diffusion properties. Fluid Phase Equil., 231, 1-10. 

Molality is a satisfactory unit of concentration for dilute solutions. However, if we wish to cover the entire range of concentrations from pure solute to pure solvent it becomes unsatisfactory. (For pure solute, the solute molality is infinite ) A more convenient plot to work with is one of (property) per mol vs. mol fraction. For (property) = volume this is shown for the ethanol-water mixture in Figure 6.5. 

The limit between - oligosaccharides and p. is primarily determined by the molecular properties. Solubility in an 80%(v/v) ethanol-water mixture is frequently used as an empirical characteristic of oligosaccharides. 

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