Solute solubility

It is important to distinguish between absolute solubility, which is defined by a K p value or similar parameter, and relative solubility, which is defined by a partition coefficient. The former is treated in this section, and the latter analyzed below. Quantitative data for the types of solutes of greatest utility for fluorous chemistry are unfortunately scarce. Tables of solubilities of representative monofunctional fluorous and non-fluorous molecules, for example, would be exceedingly useful. 

2-trifluoroethyl trifluoroacetate CF3CO2CH2CF3 7.74 ethyl acetate CH3CO2CH2CH3 6.96 

One way to conceptualize this phenomenon is to view the ponytails as short pieces of Teflon, which does not dissolve in any common solvent. As the ponytails become longer, some physical properties of the molecule approach those of Teflon. However, just as the miscibilities of fluorous liquid phases and organic liquid phases are highly temperature dependent, so are the solubilities of fluorous solids in fluorous or non-fluorous liquid phases. Hence, much higher solubilities can be achieved at elevated temperatures. This phenomenon can be used to conduct homogeneous reactions at elevated temperatures, with catalyst or reagent recovery by solid/liquid phase separation at lower temperatures.  

The solubilities of many small molecules in fluorous solvents have been measured. For example, a solution of perfluoroheptane that is saturated with octane contains 11.2 mol% octane at 27.5°C, 31.8 mol% octane at 60.0°C and 45.1 mol% octane at 65.8°C. The smaller hydrocarbon heptane is approximately twice as soluble (21.4 mol% at 11.VC) and similar to chloroform (22.4 mol% at 24.6°C). The data for octane demonstrate the strong temperature dependence of solubilities in fluorous phases. 

The solubilities of small molecules in fluorous solvents are determined to a large extent by two parameters solute polarity and size. The first is an extension of the like dissolves like paradigm. The second is uniquely important to perflu-orinated solvents because of low intermolecular forces they have large cavities (free volumes) that can accommodate small molecules. The solubilities of gases in fluorocarbons are also well established and show a correlation with the isothermal compressibility of the solvent, supporting the cavity-based solubility model. 

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Tin IV) chloride, SnCU, stannic chloride. M.p. — 33" C, b.p. 1I4°C. Colourless fuming liquid (Sn plus CI2) hydrolysed in water but forms SnCl4,5H20 and [SnCl p" from acid solutions, soluble in organic solvents. Used as a mordant. 

The term solubility thus denotes the extent to which different substances, in whatever state of aggregation, are miscible in each other. The constituent of the resulting solution present in large excess is known as the solvent, the other constituent being the solute. The power of a solvent is usually expressed as the mass of solute that can be dissolved in a given mass of pure solvent at one specified temperature. The solution s temperature coefficient of solubility is another important factor and determines the crystal yield if the coefficient is positive then an increase in temperature will increase solute solubility and so solution saturation. An ideal solution is one in which interactions between solute and solvent molecules are identical with that between the solute molecules and the solvent molecules themselves. A truly ideal solution, however, is unlikely to exist so the concept is only used as a reference condition. 

Raising T favors solution solubility rises as T rises. 

Pb2+ Tartrate buffer or chloride solution (solubility limits the amount of lead to less than 50 mg per 100 mL) 2 A 2-3 V... 

A compound whose solubility increases with temperature can be purified by recrystallization. The impure solid is dissolved in a minimum volume of hot water. The hot solution is filtered to remove insoluble impurities, and then the solution is cooled in an ice bath. The solubility of the compound decreases as the temperature drops, causing the substance to precipitate from solution. Soluble impurities usually remain in solution. Purification by recrystallization is not restricted to aqueous solutions. An organic solid can be purified by recrystallization from an appropriate organic solvent. 

In a saturated solution, solubility, S, at a particular pH is defined as the sum of the concentrations of all of the species dissolved in the aqueous solution ... 

Particulate bridging agent Aqueous ammonium salt clean-up solution Solubility [g/lOOml]... 

Solutions are mixtures, and therefore do not have definite compositions. For example, in a glass of water it is possible to dissolve 1 teaspoonful of sugar or 2 or 3 or more. However, for most solutions there is a limit to how much solute will dissolve in a given quantity of solvent at a given temperature. The maximum concentration of solute that will dissolve in contact with excess solute is called the solubility of the solute. Solubility depends on temperature. Most solids dissolve in liquids more at higher temperatures than at lower temperatures, while gases dissolve in cold liquids better than in hot liquids. 

Table 3.8. Possible soil solution solubility controls for selected trace elements3...

The most important aspect of the simulation is that the thermodynamic data of the chemicals be modeled correctly. It is necessary to decide what equation of state to use for the vapor phase (ideal gas, Redlich-Kwong-Soave, Peng-Robinson, etc.) and what model to use for liquid activity coefficients [ideal solutions, solubility parameters, Wilson equation, nonrandom two liquid (NRTL), UNIFAC, etc.]. See Sec. 4, Thermodynamics. It is necessary to consider mixtures of chemicals, and the interaction parameters must be predictable. The best case is to determine them from data, and the next-best case is to use correlations based on the molecular weight, structure, and normal boiling point. To validate the model, the computer results of vapor-liquid equilibria could be checked against experimental data to ensure their validity before the data are used in more complicated computer calculations. 

Grathwohl (1990) found a relationship between sorption capacity and the the atomic H/O ratio of NOM. Similarly, there is a good relationship between log Koc and the polarity index (PI) of SOM, defined as the (0+N)/C ratio (DePaolis and Kukkonen 1997 Rutherford et al. 1992 Xing 1997 Xing et al. 1994a). The effect of SOM polarity on sorption of organic compounds is consistent with the well-known theory of solvent polarity on solute solubility. In studying the influence of SOM composition... 

The method of concentration measurement of the saturated solution depends on the solute solubility and its chemical properties. Some common methods used for solubility measurement are listed below. 

A number of methods provide data consistent with the diblock nature of this new copolymer, including molecular weight, thermal, and solution solubility behavior. 

The comonomer composition distributions of these two materials are also indicative of the block architecture of the OBC. A comparison of solution solubility characteristics as revealed by TREF is shown in Fig. 25. The physical blend displays a peak at 96 °C with a soluble fraction of 56 wt%, consistent with a physical blend of HDPE and VLDPE. The trace from the diblock OBC reveals a peak at a slightly lower temperature, 93 °C, with no evidence of a shoulder at higher temperature that could be attributed to uncoupled HDPE. In contrast to the blend, the majority of this sample, 84 wt%, elutes at this high temperature, while only 13 wt%... 

Fig. 25 Comparison of solution solubility by analytical TREF of the blend and diblock OBC...

Given the interest in extended carbon systems in recent years, it seemed useful to study the solubility of C60 (fullerene) in various organic liquids.54 55 It was now for the solvents that the molecular surface properties were computed. The resulting Eq. (14) shows that, for this large nonpolar solute, solubility is enhanced by solvent molecule surface area and by the latter having somewhat... 

The solubility values are functions of pure component properties of the solute (a// /uv, 7ffl ) and the liquid phase activity coefficients of the components in solution. Solubility is calculated using the following equation... 

Di-isopropyl phosphorofluoridate is a practically odourless, mobile liquid, b.p. 183°/760 mm. (by extrapolation), f.p. ca. -82°. This wide range of temperature over which the compound is liquid adds to its usefulness. A specimen of the pure liquid has remained unchanged in a glass vessel for several years. Whereas the phosphorochloridate was readily hydrolysed by water, hydrolysis of the phosphorofluoridate was slow and took 72 hr. for completion at 15° and then only in the presence of a large excess of water (1 per cent solution solubility 1-5 per cent) P(OPr<)2 of+hso - P(OPrf)2 oh + hf. 

To calculate the multicomponent vapor-liquid equilibrium, equilibrium constants for chemical reactions 1-9 are taken from literature in comparison to the original publication, in the present work different numerical values for the second dissociations of hydrogen sulfide and sulfur dioxide were chosen (cf. Appendix III). Henry s constants are evaluated from single solute solubility data without neglecting Poynting corrections ... 

Parameters 0 - for interactions between like molecules were evaluated from single solute solubility data in water. These parameters proved to depend on temperature (cf. Appendix III). Parameters for... 

Soxhlet extraction is commonly used for the extraction of non-polar and semi-polar trace organics from a wide variety of solid phases (i.e., sediments, soils, etc.) [192, 366, 380, 400-404]. The size of the systems can vary, but the more common configurations use between 100 ml and 200 ml of solvent to extract 20-200 g of sample. Larger systems can be used, but require proportionally more solvent. It is essential to match the solvent polarity to the solute solubility and to wet the matrix thoroughly with the solvent when extraction commences. 

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