Temperature Dependence of Aqueous Solubility

AQUAFAC Approach The AQUAFAC approach is based on the following solubility equation [48,49]  

Aqueous solubility either increases or decreases with increasing temperature, depending on the considered temperature interval and the type of compounds. The temperature-dependence of the mole fraction aqueous solubility, Xs, for the equilibrium between organic phase and aqueous solution may be expressed by the van t Hoff equation  

Wauchope and Getzen [52] employ a semiempirical function including the molar heat of fusion to fit Xw =f(T) for PAHs. May et al. [53] employ an empirical, cubic temperature function for PAHs. A quadratic function has been derived by Yaws et al. [29] for alkanes (C5-C17) and cycloalkanes (C5-C15)  

For biphenyls, dibenzofurans, dibenzo-p-dioxins, and their halogenated derivatives, Doucette and Andren [55] fitted solubility data with the following equation  

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Dohanyosova, P., Dohnal, V., Fenclova, D. (2003) Temperature dependence of aqueous solubility of anthracenes accurate determination by a new generator column apparatus. Fluid Phase Equil. 214, 151-167. 

Shiu, W.-Y., F. Wania, H. Hung, and D. Mackay, Temperature dependence of aqueous solubility of selected chlorobenzenes, polychlorinated biphenyls, and dibenzofuran , J. Chem. Eng. Data, 42, 293-297 (1997). 

Friesen KJ, Webster GRB (1990), Environ. Sci. Technol. 24 97-101.. .Temperature dependence of aqueous solubilities of highly chlorinated dibenzo-p-dioxins ... 

TABLE 7.1.1.202.1 Reported aqueous solubilities and vapor pressures of 2,2, 3,3, 5,5, 6,6 -octachlorobiphenyl (PCB-202) at various temperatures and the reported empirical temperature dependence equations Aqueous solubility Vapor pressure ... 

Measurement of Solubility by Fluorescence Spectroscopy. Recently, Schwarz (31) has measured the temperature dependence of the solubilities of several PAHs in aqueous solutions by a fluorescence method. Saturated solutions were prepared and measured in situ in modified fluorescence cells. Each cell contained 5 mL of an aqueous solvent with an excess amount of the PAH to be studied. The cells were rotated for at least 24 hr at each temperature before the solution was allowed to settle and be measured. The fluorescent intensity of these saturated aqueous PAH solutions was found to be proportional to concentration between 8° and 30°C. The fluorescence measurements were put on an absolute scale by UV spectroscopic measurements at 25°C. 

The study of thermodynamic properties of aqueous solutions of inert gases was the subject of my PhD thesis. In the early 1960s, not much was known about these systems. Experimental data were very scarce and inaccurate. Theory was highly speculative. Nevertheless, I chose this subject mainly for one reason I was fascinated by the hearsay that inert solute dissolved in water lowers the entropy of the system. Lowering the entropy meant increasing the structure of water. But why How can inert solutes cause an increase in structure and lower the entropy That was quite a mystery. I say it was hearsay because the experimental data on solubilities of inert solutes was very inaccurate. The entropy of solution was determined from the temperature dependence of the solubility. That renders the uncertainty of the values of the entropy of solution even larger than the uncertainty of the solubilities themselves. At that time I was not aware of the fact that the so-called standard entropy of solution was itself an uncertain measure of the entropy of solvation. 

The shape of the equilibrium line, or solubility curve, is important in determining the mode of crystallization to be employed in order to crystallize a particular substance. If the curve is steep, i.e. the substance exhibits a strong temperature dependence of solubility (e.g. many salts and organic substances), then a cooling crystallization might be suitable. But if the metastable zone is wide (e.g. sucrose solutions), addition of seed crystal might be necessary. This can be desirable, particularly if a uniformly sized product is required. If on the other hand, the equilibrium line is relatively flat (e.g. for aqueous common salt... 

There have been numerous approaches to describing the temperature dependence of the properties. For aqueous solubility, the most common expression is the van t Hoff equation of the form (Hildebrand et al. 1970) ... 

Schwarz, F.P. (1977) Determination of temperature dependence of solubilities of polycyclic aromatic hydrocarbons in aqueous solutions by a fluorescence method. J. Chem. Eng. Data 22, 273-277. 

The temperature dependences of solubilities of the trichlorides of lanthanum, praseodymium, and neodymium in aqueous ammonium chloride solutions (212) are so irregular that no estimate of solution enthalpies can be made from them by the van t Hoff method. 

Let us consider the temperature dependence of the mole fraction solubility of organic liquids. Since xs /xiL = x (xlL = 1) represents the partitioning constant between the aqueous phase and the pure liquid, for a narrow temperature range, its temperature dependence is given by (Section 3.4) ... 

Friesen, K. J., and G. R. B. Webster, Temperature Dependence of the Aqueous Solubilities of Highly Chlorinated Dibenzo-p- Dioxins. Environ. Sci. Technol., 1990 24, 97-101. 

Figure 3.27 Methane hydrate film development at the water-methane interface from dissolved methane in the aqueous phase, as indicated from Raman spectroscopy (a) and methane solubility predictions (b). (a) A series of Raman spectra of dissolved methane collected at different temperatures during the continuous cooling process. Spectra marked A through E correspond to temperatures of 24°C, 20°C, 15.6°C, 10.2°C, and 2.8°C, respectively. (b) A schematic illustration of temperature dependencies of the equilibrium methane concentration in liquid water (C = without hydrate, Qjh = with hydrate). The scale of the vertical axis is arbitrary, but the Raman peak area is proportional to methane dissolved in water. Points A through F correspond to different temperatures during the continuous cooling process. (From Subramanian, S., Measurements ofClathrate Hydrates Containing Methane and Ethane Using Raman Spectroscopy, Ph.D. Thesis, Colorado School of Mines, Golden, CO (2000). With permission.)...

It is an everyday experience that calcium soaps have a low aqueous solubility while many surfactants with monovalent counterions have an extremely high solubility. As for other compounds, the solubility is to a great extent given by conditions in the solid phase, but for surfactants the strongly cooperative association produces the peculiar temperature dependence of solubility schematized in Fig. 2.8. The so-... 

TMS cannot be used in aqueous solution because it is not water soluble. For a chemical-shift reference, a water-soluble equivalent (such as sodium d4-3-trimethylsilylpropanoate ((CH3)3SiCD2CD2C02-Na l, TSP )) can be added the single H peak is defined as zero ppm in water. The water peak itself can also be used as a chemical-shift reference, but care must be taken to correct for the temperature dependence of its chemical shift. Referencing of 13C and 15N chemical shifts can be done by using an accurate H reference. If the exact chemical shift is known at the center of the H spectral window (usually the water resonance), the precise radio frequency can be calculated for the zero point of the XH chemical-shift (ppm) scale. For example, on a 600 MHz spectrometer with a reference frequency of 600.13231564 MHz and a water chemical shift of 4.755 ppm ... 

The calorimetric measurements in metal oxide-aqueous electrolyte solution systems are, beside temperature dependence of the pzc measurements, the method for the determination of the enthalpy of the reaction in this system. Because of the low temperature effects in such systems they demand very high precision. That is why these measurements may be found only in a few papers from the last ten years [89-98]. A predominant number of published measurements were made in the special constricted calorimeters (bath type), stirring the suspension. The flow calorimeters may be used only for sufficiently large particles of the solid. A separate problem is the calculation of the enthalpy of the respective reactions from the total heat recorded in the calorimeter. A total thermal effect consists of the heat of the neutralization in the liquid phase, heat connected with wetting of the solid, heat of the surface reaction and heat effects caused by the ion solvation changes (the ions that adsorb in the edl). Considering the soluble oxides, one should include the effects connected with the transportation of the ions from the solid to the solution... 

The specific heats of aqueous ions of several metals are not readily available in the literature. As a result, it is difficult to determine the temperature dependence of the thermodynamic quantities and, hence, that of the solubility product constants for these metal oxides. This dependence can be roughly determined from the general dissolution equation... 

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