Between solids and solutions

Fig. 10-2. A large energy difference between solid and solution lowers the solubility.

An electrical potential develops at all interfaces. In soil, there are interfaces between solids and solution, solution and suspension, suspension and the electrode surface, and between the reference electrode and all these interfaces. 

The Bonding between Solids and Solutes The Need for a better Understanding... 

Over the last decade, some research has indicated that (1) partition coefficients (i. e.,Kd) between solid and solution phase are not measured at true equilibrium [51,59-61], (2) the use of equilibrium rather than kinetic expressions for sorption in fate and effects models is questionable [22-24,60,61], and (3) sorption kinetics for some organic compounds are complex and poorly predictable [22 - 24,26]. This is mainly due to what has recently been discussed as slow sorp-tion/desorption of organic compounds to natural solid phase particles [107, 162-164,166-182]. The following is a summary of some important points supporting this hypothesis [1,66,67,170-183] ... 

Cluster models of mixed oxide catalysts and of relationships between solid and solution catalysts... 

For simplicity, let us consider perfectly drained conditions (p = 0) and start from an equilibrium between solid and solute (xjrc — xj/x). The equilibrium is disturbed by application of a constant macroscopic stress X = <5 ( > 0). 

Komada, T., and Reimers, C.E. (2001) Resuspension-induced partitioning of organic carbon between solid and solution phases from a river-ocean transition. Mar. Chem. 76, 155-174. 

Kirschning A, Monenshein H, Wittenberg R, The resin capture-release hybrid technique A merger between solid and solution-phase synthesis, Chem. Eur. J., 4445-4450, 2000. 

On crystallization, nonthermochromic distibines and dibismuthines show little visual change. The solid colors of two nonthermochromic distibines (8 and 9) and two nonthermochromic dibismuthines (45 and 46) have been characterized by diffuse reflectance. In each case, only very modest changes in the absorption maxima were observed and between solid and solution. On the other hand, the intense colors shown by the solid phases of the thermochromic distibines are red shifted by 200-250 nm from their solution phase maxima (see Table IV) (7,25,29,33,34,37, 38b,40). The dibismuthines are red shifted even further. There is complete correspondence between dibismuthines and the analogous distibines, with the dibismuthines being red shifted by around 100 nm (see Fig. 1). 

As the active species is formed on the electrode surface at an interface between solid and solution, unique characteristics in reactivity can occur that are useful to the organic chemist. 

This may be regarded as a distribution equilibrium of the two halide ions between solid and solution ... 

Ding M., DeJong B. H. W. S., Roosendaal S. J., and Vredenberg A. (2000) XPS studies on the electronic structure of bonding between solid and solutes adsorption of arsenate, chromate, phosphate, Pb, and Zn ions on amorphous black ferric oxyhydroxide. Geochim. Cosmochim. Acta 64, 1209-1219. 

Reactions between solids and solutions may be treated in a similar manner. Every solid has a definite solubility in every solvent, just as it has a definite vapour pressure at a given temperature. The solubility depends on the nature of the solvent and on the temperature, but is independent (in dilute solutions at least) of the presence of other dissolved or undissolved substances. So-called insoluble substances differ from soluble substances only in that their solubility is exceedingly small. 

MTien several solid substances react with one another in presence of a solvent, the condition for equilibrium may be obtained as follows. In homogeneous solutions which contain definite, although possibly very minute, concentrations of all the molecules taking part in the reaction, the law of mass action will hold, provided that the concentrations are not too high. At constant temperature, however, the concentrations of all the substances which are present in the solid state are determined by their solubilities. The constant values of these concentrations may therefore be included in the equilibrium constant, like the vapour pressures of the solid substances in the calculations of the previous paragraph. For reactions between solids and solutions the law of mass action therefore assumes the same form as for homogeneous solutions, viz. ah... 

Equation (4) illustrates the application of the phase rule to equilibria between solids and solutions. Thus the number of variable concentrations in the equilibrium equation is exactly equal to the degrees of freedom / of the system, namely, the total number n of the molecular types taking part in the reaction less the number B of the substances present in the solid phase (f=n—B) n is also the number of the independent components of the system, which is equal to the total number of molecular types present (n-f sol vent), less the number of the chemical equations (1). The number of phases is P = B+2 (solution and vapour). Hence... 

Table 5.14. The increase in the solubility on the formation of the hydrochloride is readily attributable in the case of tetracycline to a lowering of the solution pH by the hydrochloride. The common ion effect can, however, produce an unexpected trend in the solubilities of bases in the presence of high concentrations of hydrochloric acid. Increase in Cl concentrations will cause the equilibrium between solid and solution forms...

The pathways of chemical reactions can be investigated using radioactive tracers. When radioactive 2- j-g added to a saturated solution of cobalt sulfide in equilibrium with solid cobalt sulfide, the solid becomes radioactive. This shows that sulfide ion exchange occurs between solid and solution in the solubility equilibrium. 

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