Liquid and Solid Solubilities

A second example of a binary system in which one component is considered to be confined to one phase only involves the solubility of liquids and solids in a solvent. The confined species here is the solvent, which is in contact with a second phase containing a pure liquid or solid. At equilibrium the solvent phase has become saturated with the dissolved species or solute and no further dissolution takes place. The concentration corresponding to this state is termed the solubility of the liquid or solid in question. 

The number of possible solute-solvent combinations is evidently quite large, and the corresponding number of required measurements infinite if temperature is considered an additional variable. It is customary therefore to deal with only a small number of solvents, principally water, and to perform measurements at a standard temperature of 25dC. Most reported data have been obtained within this framework. 

Illustration 6.5 Discharge of Plant Effluent into a River 

We consider here the case of process water saturated with benzene being discharged into a river. The question to be addressed is whether the diluting 

Mass Transfer and Separation Processes Principles and Applications 

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A general reference often consulted today for the physical and chemical properties of common chemicals is Lange s Handbook of Chemistry (Dean 1999), which lists many chemical compounds and their most important properties. It is organized into separate chapters of Physical constants of organic molecules with 4300 compounds and Physical constants of inorganic molecules, and lists each compound alphabetically by name. Some of these properties are very sensitive to temperature, but less sensitive to pressure, and they are listed as tables, or more compactly as equations of the form /(T) for example, liquid heats of evaporation, heat capacities of multi-atom gases, vapor pressures over liquids, liquid and solid solubilities in liquids, and liquid viscosities. Some of these properties are sensitive both to temperature and pressure. 

For gas, liquid and solid solubilities in water it is best to draw on environmental source books, among which the monumental treatise by Mackay... 

Typical phase diagram of a binary system with complete liquid and solid solubility. The first-to-freeze component will have composition Cl. The rejected B component will be pushed ahead of the solidification front and, if convectively mixed with the remaining melt, the solid will become richer in 6 as the process continues. 

The liquid L is a homogeneous liquid solution composed of both copper and nickel. The a phase is a substitutional solid solution consisting of both Cu and Ni atoms and has an FCC crystal structure. At temperatures below about 1080°C, copper and nickel are mutually soluble in each other in the solid state for all compositions. This complete solubility is explained by the fact that both Cu and Ni have the same crystal structure (FCC), nearly identical atomic radii and electronegativities, and similar valences, as discussed in Section 4.3. The copper-nickel system is termed isomorphous because of this complete liquid and solid solubility of the two components. 

A wide variety of physical properties are important in the evaluation of ionic liquids (ILs) for potential use in industrial processes. These include pure component properties such as density, isothermal compressibility, volume expansivity, viscosity, heat capacity, and thermal conductivity. However, a wide variety of mixture properties are also important, the most vital of these being the phase behavior of ionic liquids with other compounds. Knowledge of the phase behavior of ionic liquids with gases, liquids, and solids is necessary to assess the feasibility of their use for reactions, separations, and materials processing. Even from the limited data currently available, it is clear that the cation, the substituents on the cation, and the anion can be chosen to enhance or suppress the solubility of ionic liquids in other compounds and the solubility of other compounds in the ionic liquids. For instance, an increase in allcyl chain length decreases the mutual solubility with water, but some anions ([BFJ , for example) can increase mutual solubility with water (compared to [PFg] , for instance) [1-3]. While many mixture properties and many types of phase behavior are important, we focus here on the solubility of gases in room temperature IFs. 

The principal experimental method used to measure the density of a solid is determination of the mass of liquid displaced by a known mass of solid. It is essential that the solid have no appreciable solubility in the liquid, that all occluded air be removed from the solid and that the density of the displacement fluid be less than that of the solid lest the solid float. Densities of crystalline solids also can be determined from the dimensions of the unit cell. Davis and Koch discuss other methods for measuring the density of liquids and solids such as hydrostatic weighing of a buoy and flotation methods. 

A great many electrolytes have only limited solubility, which can be very low. If a solid electrolyte is added to a pure solvent in an amount greater than corresponds to its solubility, a heterogeneous system is formed in which equilibrium is established between the electrolyte ions in solution and in the solid phase. At constant temperature, this equilibrium can be described by the thermodynamic condition for equality of the chemical potentials of ions in the liquid and solid phases (under these conditions, cations and anions enter and leave the solid phase simultaneously, fulfilling the electroneutrality condition). In the liquid phase, the chemical potential of the ion is a function of its activity, while it is constant in the solid phase. If the formula unit of the electrolyte considered consists of v+ cations and v anions, then... 

At least two correlation studies on the aqueous solubilities of liquid organic compounds have been published [18, 19], and in each case an excellent correlation (r > 0.9) was obtained. For both liquid and solid compounds, log P or CLOGP accounts for a major portion of variance in water solubility [3, 4, 20]. However, the... 

Hildebrand, J. H., Prausnitz, J. M., Scott, R. L. (1970) Regular and Related Solutions. The Solubility of Gases, Liquids, and Solids. Van Nostrand Reinhold. Co., New York. 

The solubility of liquids and solids are, in general, not affected by changes in pressure. However, the solubility of gases is affected. The greater the pressure is, the greater the solubility of the gas in a liquid. 

The unique ability of crown ethers to form stable complexes with various cations has been used to advantage in such diverse processes as isotope separations (Jepson and De Witt, 1976), the transport of ions through artificial and natural membranes (Tosteson, 1968) and the construction of ion-selective electrodes (Ryba and Petranek, 1973). On account of their lipophilic exterior, crown ether complexes are often soluble even in apolar solvents. This property has been successfully exploited in liquid-liquid and solid-liquid phase-transfer reactions. Extensive reviews deal with the synthetic aspects of the use of crown ethers as phase-transfer catalysts (Gokel and Dupont Durst, 1976 Liotta, 1978 Weber and Gokel, 1977 Starks and Liotta, 1978). Several studies have been devoted to the identification of the factors affecting the formation and stability of crown-ether complexes, and many aspects of this subject have been discussed in reviews (Christensen et al., 1971, 1974 Pedersen and Frensdorf, 1972 Izatt et al., 1973 Kappenstein, 1974). 

Regular and Related Solutions. The Solubility of Gases, Liquids and Solids" Van Nostrand Reinhold,... 

The diagrams that will be mainly considered are those concerning the behaviour of the alloys in the liquid and solid states that is, melting and solid-state transformation diagrams. A number of different diagram types can be defined and classified on the basis of the different mutual solubility of the components (in the liquid and in the solid state with the formation of more or less extended liquid and/or solid solutions) and of their reactivity, resulting in the formation of various, so-called intermediate phases . 

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