Solubility and the Solution Process

Very little happens to simple molecules, such as N2 and O2, when they dissolve in water. They mingle with the water molecules and occupy spaces that open up between water molecules to accommodate the N2 and O2 molecules. If the water is heated, some of the gases are driven out of solution. This may be observed as the small bubbles that appear in heated water just before it boils. A fish can extract some of the oxygen in water by breathing through its gills just 6 or 7 parts of oxygen in a million parts of water is all that fish require. Water saturated with air at 25°C 

The solution of hydrogen chloride in water illustrates a case in which a neutral molecule dissolves and forms electrically charged ions in water. While this happens with other substances dissolved in water, the hydrogen ion resulting when substances such as HCl dissolve in water is particularly important because it results in the formation of a solution of acid. So, rather than calling this a solution of hydrogen chloride, it is called a hydrochloric add solution. 

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Next we study the formation of solutions at the molecular level and see how intermolecular forces affect the energetics of the solution process and solubility. (12.2)... 

Describe the role of equilihrium in the solution process and its relationship to the solubility of a solute. (Section 13.2)... 

Although the data for the silver halides suggest that silver(I) fluoride is likely to be more soluble than the other silver halides (which is in fact the case), the hydration enthalpies for the sodium halides almost exactly balance the lattice energies. What then is the driving force which makes these salts soluble, and which indeed must be responsible for the solution process where this is endothermic We have seen on p. 66 the relationship AG = — TAS and... 

From the standpoint of thermodynamics, the dissolving process is the estabHsh-ment of an equilibrium between the phase of the solute and its saturated aqueous solution. Aqueous solubility is almost exclusively dependent on the intermolecular forces that exist between the solute molecules and the water molecules. The solute-solute, solute-water, and water-water adhesive interactions determine the amount of compound dissolving in water. Additional solute-solute interactions are associated with the lattice energy in the crystalline state. 

Dyes, on the other hand, ate colored substances which ate soluble or go into solution during the appHcation process and impart color by selective absorption of light. In contrast to dyes, whose coloristic properties ate almost exclusively defined by their chemical stmcture, the properties of pigments also depend on the physical characteristics of its particles. 

Vitreous sihca does not react significantly with water under ambient conditions. The solution process involves the formation of monosilicic acid, Si(OH)4. Solubihty is fairly constant at low pH but increases rapidly when the pH exceeds 9 (84—86). Above a pH of 10.7 sihca dissolves mainly as soluble sihcates. Solubihty also increases with higher temperatures and pressures. At 200—400°C and 1—30 MPa (<10 300 atm), for example, the solubihty, S, of Si02 in g/kg H2O can be expressed as foUows, where d ls the density of the vapor phase and T is the absolute temperature in Kelvin. 

The ease with which dissolution of the acetylated products can be achieved is affected by the method of isolation. In the author s experience, drying of the acetate with alcohol and ether results in apparent insolubility (even though the product was soluble at one stage of the purification process), and should be avoided. Drying, under diminished pressure, of the product precipitated by petroleum ether is sufficient. Chloroform is probably the best solvent. Nitroethane, tetrachlorethane, 2,4-pentanedione, pyridine, methyl acetate, ethyl acetate, and benzene, which have also been suggested, have disadvantages in that either they are unstable or they may cause aggregation in solution.44,116 116... 

Table III gives values of the changes in Gibbs energy, enthalpy, entropy, and heat capacity of the solution process as calculated from the equations of Table I. Figure 1 shows the recommended noble gas mole fraction solubilities at unit gas partial pressure (atm) as a function of temperature. The temperature of minimum solubility is marked.

The solid sulfur product need not be chosen as an unknown. Near room temperature, only a small percentage of it is oxidized to soluble sulfur-containing anions(4). It can be assumed, therefore, that none of the sulfur atoms originally present in the solid chalcopyrite enter the solution. The sulfur product is not recovered in the leaching process and does not affect the solution chemistry. 

In many cases the CALPHAD method is applied to systems where there is solubility between the various components which make up the system, whether it is in the solid, liquid or gaseous state. Such a system is called a solution, and the separate elements (i.e., Al, Fe...) and/or molecules (i.e., NaCl, CuS...) which make up the solution are defined as the components. The model description of solutions (or solution phases) is absolutely fundamental to the CALPHAD process and is dealt with in more detail in chapter S. The present chapter will discuss concepts such as ideal mixing energies, excess Gibbs energies, activities, etc. 

Commerical polymerizations of ethylene, propene, and other a-olefins are carried out as slurry (suspension) and gas-phase processes [Beach and Kissin, 1986 Diedrich, 1975 Lieberman and Barbe, 1988 Magovern, 1979 Vandenberg and Repka, 1977 Weissermel et al., 1975]. Solution polymerization has been used in the past for ethylene polymerization at 140-150°C, pressures of up to 8 MPa (1 MPa = 145 psi = 9.869 atm), using a solvent such as cyclohexane. The solution process with its higher temperatures was employed for polymerization with the relatively low efficiency early Phillips initiators. (Polyethylene, but not the initiator, is soluble in the reaction medium under the process conditions.) The development of a variety of high-efficiency initiators has allowed their use in lower-temperature suspension and gas-phase processes, which are more advantageous from many... 

The adsorption of hafnium species on glass was found to increase with the solution pH and hafnium concentration. The effects on the adsorption of the solution preparation and age were studied and the equilibration time for the adsorption process was determined. The surface area of the glass sample was determined by the B.E.T. method using water vapor. The results are discussed in terms of the hydrolyzed hafnium(IV) species. At equilibrium, nearly monolayer coverage was obtained at pH > 4.5. Under these conditions hafnium is in the solution in its entirety in the form of neutral, soluble Hf(OHspecies. In the close packed adsorption layer the cross-sectional area of this species is 24 A which is nearly the same as for water on silica surfaces. 

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