The Ethanol-Water System

If you look up the solubility of water in ethanol (or ethanol in water) you find an a . This means they mix in all proportions. Any amount of one dissolves 

From this, you should get the idea that it would be good to use a mixed solvent to recrystallize compounds that are soluble in alcohol yet insoluble in water. You see, each solvent alone cannot be used. If the material is soluble in the alcohol, not many crystals come back from alcohol alone. If the material is insoluble in water, you cannot even begin to dissolve it. So, you have a mixed solvent, with the best properties of both solvents. To actually perform a mixed-solvent recrystallization you 

Add hot water until the solution turns cloudy. This cloudiness is tiny crystals of compound coming out of solution. Heat this solution to dissolve the crystals. If they do not dissolve completely, add a very little hot ethanol to force them back into solution. 

Any solvent pair that behaves the same way can be used. The addition of hot solvents to one another can be tricky. It can be extremely dangerous if the boiling points of the solvents are very different. For the water-methanol mixed solvent, if 95 °C water hits hot methanol (B.P. 65.0 °C), watch out  

There are other miscible, mixed-solvent pairs, pet. ether and diehyl ether, methanol and water, and ligroin and diethyl ether among them. 

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The type of behavior shown by the ethanol-water system reaches an extreme in the case of higher-molecular-weight solutes of the polar-nonpolar type, such as, soaps and detergents [91]. As illustrated in Fig. Ul-9e, the decrease in surface tension now takes place at very low concentrations sometimes showing a point of abrupt change in slope in a y/C plot [92]. The surface tension becomes essentially constant beyond a certain concentration identified with micelle formation (see Section XIII-5). The lines in Fig. III-9e are fits to Eq. III-57. The authors combined this analysis with the Gibbs equation (Section III-SB) to obtain the surface excess of surfactant and an alcohol cosurfactant. 

Kirschbaum (DistiUier-Rektifizieii echnik, 4th ed.. Springer-Verlag, Berhn and Heidelberg, 1969) reported on studies of the ethanol-water system at atmospheric pressure, using several columns. For a... 

This procedure is commonly used to calculate vapor pressures and activities for volatile mixtures. For example, it was used to determine the vapor pressures for the (ethanol + water) system shown in Figure 6.7. 

Excess Volume Comparison Figure 7.5 compares V for the three systems for which we have compared H, G, and 5, plus the (cyclohexane + decane) system.5 The comparatively large negative for the (ethanol + water) system curve (4) can be attributed to the decrease in volume resulting from the formation of hydrogen-bonded complexes in those mixtures. The negative for the (hexane + decane) system curve (3) reflects an increased packing... 

The results for (cyclohexane + decane) are obtained from J. R. Goates. J. R. Ott, and R. B. Grigg, "Excess Volumes of Cyclohexane 4- u-Hexane. +u-Heptane, -t-n-Octane, + -Nonane, and +u-Decane", J. Chem. Thermodyn.. 11. 497-506 (1979). Excess volumes for the (ethanol + water) system were obtained from K. N. Marsh and A. E. Richards, Excess Volumes for Ethanol + Water Mixtures at 10-K intervals from 278.15 to 338.15 K", Ausr. J. Chem., 33, 2121-2132 (1980). Excess volumes for the (acetonitrile + benzene) and the (hexane + decane) systems were obtained from the same source as the HG and results referenced earlier. 

For non-ideal solutions, such as the ethanol-water system, at the intermediate ethanol concentrations found in the bed and the condensate during anaerobic gas-solid fluidized bed fermentafions, Raoult s law (equation 4.2) is inadequate and an activity coefficient ymust be introduced, so that the partial pressures of efhanol pe and water p over an ethanol-water solution are given by equation 6.11... 

The presence of solutes other than ethanol might be expected to reduce the mole fractions of ethanol and water and influence the nonideality of the ethanol-water system. However, both Williams (1983), who modelled a batch wine fermentation, and Rottenbacher (1985), in ethanol sorption experiments with yeast pellets in a fluidized bed, established that the ethanol-water-yeast system behaves as if the water and ethanol content of the pellets were a simple ethanol-water solution supported by a solid matrix which influences neither mole fractions nor activity coefficients. 

The absolute value of (l/e Ae/Axi) is the greatest in the ethyl acetate-methanol system but becomes smaller in the ethanol-water system and methanol-water system, in that order. In solvent systems, the greater the value of the right hand side of Equation 1, the greater the value of X2A20 but smaHer the value of In other words, the preferential solvation due to methanol or... 

Vapor-Liquid Equilibrium in the Ethanol-Water System Saturated with Chloride Salts... 

The present work studies the vapor-liquid equilibrium of the ethanol-water system saturated with copper(II) chloride, strontium chloride, and nickel(II) chloride. 

From experimental data for the ethanol-water system without salt, obtained at 700 and 760 mmHg, it can be seen that within this pressure range the effects of pressure on the equilibrium data are small enough to be within the experimental scatter. In fact, in previous works (8,11,12,13,18,19,23,24,27) there seems to be no clear difference between the equilibrium data at 700 and at 760 mmHg. Errors obtained in the determination of liquid and vapor compositions are approximately 0.05 wt % for the systems without salt. For salt-saturated systems, the same error prevails for the vapor phase, while the error is between 0.1 and 0.2 wt % for liquid phase compositions. The error for the boiling temperature is less than 0.1 °C for the systems without salt, but for saturated solutions the error is much greater from 0.2°C for nonconcentrated solutions to 3°C or more for highly concentrated solutions. 

Figure 2. Temperature-composition diagrams, corrected to 700 mmHg, for the ethanol-water systems saturated with copper(II) chloride, nickel(II) chloride, and strontium chloride...

The exponent n indicates the deviation of the system with salt from the salt-free system. Figure 7 shows the values of log TryjPp vs. log (Xsi7i°) for the ethanol-water system saturated with copper(II) chloride, nickel(II) chloride, and strontium chloride respectively. The values for n obtained from the above system are shown in Table II. 

In Table XVIII, there are several trends that can be noted in k if one proceeds through the R4NBr series. First of all, k tends to decrease as the size of the TAA cation increases and, in fact, tetra-n-butylammonium bromide shows a large salting-in effect. This trend is emphatically demonstrated by Figure 13, which shows the smoothed salt effects of the various salts studied in the ethanol-water system at x = 0.206. Secondly, it appears that there is a larger salting-out effect as the mole fraction of ethanol increases in the binary solvent mixture. 

Figure 1. Salt effect of KBr in the ethanol-water system at x...

In examining the sensitivity of the model to the assumed value of z, it was found for the ethanol-water system that the goodness of fit of the model was insensitive to the z value in the vicinity of z-10. For large values of z (z>15), however, it was found that the model was incapable of even qualitatively prediciting mixture VLE behaviour. 

Discussion There are two ways of treating this system and they should give identical results. If we consider NaCl as a single un-ionized substance, the system has two independent components, which form a solution (assuming that we have not exceeded the solubility limit). There is, thus, two degrees of freedom, just as in the ethanol-water system. Alternatively, we can treat NaCl as an electrolyte, which is completely ionized in solution. Then, there are actually three components, Na+,... 

Figure 13.5 shows experimental heats of mixing AH (or excess enthalp He) for the ethanol/water system as a function of composition for seve" temperatures between 30 and 110°C. This figure illustrates much of the vari of behavior found for HE = AH and Vh - A V data for binary liquid system... 

Vapor-liquid equilibrium data for the ethanol/water system (subscripts 1 and 2, respectively) at 70°C (158°F, 343 K) are given in the three left columns of Table 3.1. Check to see if the data are thermodynamically consistent. 

Calculate the Wilson constants for the ethanol/water system using the infinite-dilution activity coefficients calculated in the preceding example y,00 = 5.75 and y2°° = 2.48, with subscript 1 pertaining to ethanol. 

To illustrate how large the effect of a dissolved salt can be, Figure 2, calculated from the data of Meranda and Furter (I), is included to demonstrate by how much potassium acetate alters the vapor-liquid equilibrium relationship of the system, boiling ethanol-water at atmospheric pressure. The dotted curve represents the ethanol-water system alone, where the azeotrope occurs at about 87 mole % ethanol. The other curves are for various concentrations of potassium acetate, and all are... 

To illustrate the consistency between the two programs, data for the ethanol-water system reported by Rieder and Thompson (11) were used. The first program estimated the values of the energy parameters and calculated the vapor-phase composition, y, with a root mean square deviation (RMSD) of 0.00847. The mean arithmetic deviation between the... 

The method described above is applied to the ethanol-water system which has been saturated in turn with each of a wide range of inorganic salts. The vapor pressure of water saturated with salts over a temperature range is available for many salts (4). For ethanol these data are unavailable, and a correction to the saturation vapor pressure is applied by multiplying by the ratio of the vapor pressure of ethanol saturated... 

Figure 1. Comparison of the experimentally determined vapor compositions for the ethanol-water system (8) with two constant Wilson T-x fit...

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