Liquid phase solubilities

Brian, P. L. T. (1965) Ind. Eng. Chem. Fundamentals 4, 100. Predicting activity coefficients from liquid phase solubility limits. 

The chemistry of soil is contained in the chemistry of these three phases. For the solid phase, the chemistry will depend on the amount and type of surface available for reaction. In the liquid phase, solubility will be the most important characteristic for determining the chemistry occurring. In the gaseous phase, gas solubility and the likelihood that the component can be in the gaseous form (i.e., vapor pressure) will control reactivity. 

Reactions taking place on the surface of solid or liquid particles and inside liquid droplets play an important role in the middle atmosphere, especially in the lower stratosphere where sulfate aerosol particles and polar stratospheric clouds (PSCs) are observed. The nature, properties and chemical composition of these particles are described in Chapters 5 and 6. Several parameters are commonly used to describe the uptake of gas-phase molecules into these particles (1) the sticking coefficient s which is the fraction of collisions of a gaseous molecule with a solid or liquid particle that results in the uptake of this molecule on the surface of the particle (2) the accommodation coefficient a which is the fraction of collisions that leads to incorporation into the bulk condensed phase, and (3) the reaction probability 7 (also called the reactive uptake coefficient) which is the fraction of collisions that results in reactive loss of the molecule (chemical reaction). Thus, the accommodation coefficient a represents the probability of reversible physical uptake of a gaseous species colliding with a surface, while the reaction probability 7 accounts for reactive (irreversible) uptake of trace gas species on condensed surfaces. This latter coefficient represents the transfer of a gas into the condensed phase and takes into account processes such as liquid phase solubility, interfacial transport or aqueous phase diffusion, chemical reaction on the surface or inside the condensed phase, etc. 

Starting Materials. Polyethylene, low density (0.92), was obtained from Union Carbide as additive-free pellets. Copper propionate, used only for liquid-phase solubilities, was obtained commercially and used without further purification. All other copper salts were synthesized as follows equal equivalents of Cu(OH)2 CuC03 ( 99+%, ROC/RIC Chemical Corp.) and the appropriate carboxylic acid were stirred in a minimum amount of xylene and heated to 120°C under N2 overnight. After reacting the xylene solution was diluted with additional xylene, reheated, and filtered hot to remove any copper oxides and/or carbonates. The xylene solution was cooled and the resultant precipitate collected by suction filtration and washed with additional xylene and then hexane. Additional recrystallization was done from hexane, isooctane, and/or xylene. In the case of the copper octanoate the solubility in xylene was quite high, so minimum amounts were used and recrystallization was done from hexane. Analyses for copper Cu(C7Hi5C02)2,... 

Solubilities. Extrapolation from Liquid Phase. Solubilities of various copper carboxylate salts in pure octane and hexadecane at 90 °C are shown in Figure 2. The solubility of the octanoate salt is quite high but cannot be measured accurately because of experimental difficulties (discussed above). If one applies regular solution theory (6) with the assumption that the excess free energies of mixing (or alternatively the solvent-solute interaction parameters) are equal for a particular salt in an alkane medium, then the following equation can be derived (7) ... 

In most circumstances other processes, such as gas-phase diffusion to the droplet surface and liquid-phase solubility, also limit gas uptake. In a laboratory experiment a can generally not be measured directly. Rather, what is accessible is the measured overall flux of gas A to the droplet (mol A per area per time). That flux can be expressed in terms of a measured uptake coefficient, y < 1, that multiplies the kinetic collision rate per unit of droplet surface area as... 

A particularly interesting compound in this context is C12E3, which displays a lamellar liquid-crystal solubility boundary at room temperature, an L3 solubility boundary between 39°C and 58°C, and a concentrated liquid-phase solubility boundary >58 C. The change in the qualitative nature of the solubility boundary from the lamellar liquid crystal to the L3 liquid profoundly alters the swelling behavior of this compound [71]. 

The temperature of operation should be high enough to ensure solubility of all solutes at the concentrations encountered in both liquid phases. Solubility of a solute is only slightly influenced by pressure. This effect can be predicted from the principle of Le Chatelier. If the volume of the liquid phase increases with an increase in solute concentration, a higher pressure of operation will decrease solubility. 

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