Equilibrium distribution of a solute between

The equilibrium distribution of a solute between immiscible solvents is expressed by the distribution (or partition) coefficient (K) which is the ratio of... 

The term partition coefficient refers to the equilibrium distribution of a solute between two phases separated by a boundary. In this case, the two phases are the solid plastic and seawater. Any compound (such as a POP) in seawater wiU readily diffuse into the hydrophobic plastic as well resulting in an equilibrium concentration of the compound in the plastic will be very much higher than that in seawater (Ogata et al., 2009). The partition coefficient is the ratio of the concentrations, and in the case of plastics in seawater can be expressed as follows ... 

Figure 5.1 Equilibrium distribution of a solute between a gas and a liquid phase at con.stant tute.

The governing criterion for equilibrium distribution of a solute between an ion exchange resin and an external solution is relation (3.3.8) when the solute is a weak electrolyte or a nonelectrolyte. The namre of the equilibrium is similar to that with nonionic adsorbents. When the solute is a strong electrolyte, criterion (3.3.29) has to be used due to the presence of fixed ionic charges and counterions in the resin. 

An equilibrium constant describing the distribution of a solute between two phases only one form of the solute is used in defining the partition coefficient... 

The distribution coefficient is an equilibrium constant and, therefore, is subject to the usual thermodynamic treatment of equilibrium systems. By expressing the distribution coefficient in terms of the standard free energy of solute exchange between the phases, the nature of the distribution can be understood and the influence of temperature on the coefficient revealed. However, the distribution of a solute between two phases can also be considered at the molecular level. It is clear that if a solute is distributed more extensively in one phase than the other, then the interactive forces that occur between the solute molecules and the molecules of that phase will be greater than the complementary forces between the solute molecules and those of the other phase. Thus, distribution can be considered to be as a result of differential molecular forces and the magnitude and nature of those intermolecular forces will determine the magnitude of the respective distribution coefficients. Both these explanations of solute distribution will be considered in this chapter, but the classical thermodynamic explanation of distribution will be treated first. 

If the activity of a solute is known in one solvent, then its activity in another solvent immiscible with the hrst can be determined from the equilibrium distribution of the solute between the two solvents. As an example, let us consider an extreme situation, such as that illustrated in Figure 17.7, in which the shapes of the fugacity curves are different in two different solvents. The limiting behavior at inhnite dilution, Henry s law, is indicated for each solution. The graphs reveal that the standard states are different in the two solvents because the hypothetical l-moM solutions have different fiigacities. 

The equilibrium distribution of a solute B between water and an organic solvent is described by the partition constant or by its function, the free... 

There is an equilibrium distribution of a solute species A between phases Of and f if the phases are in contact for a long time. We consider this a reaction ... 

When we are interested in the equilibrium distribution of a chemical between the solids and solution present in any particular volume of an aquatic environment, we begin by considering how the total sorbate concentration, C,s (e.g., mol-kg-1), depends on chemical s concentration in the solution, C,w (e.g., mol-L ). The relationship of these two concentrations is commonly referred to as a sorption isotherm. The name isotherm is used to indicate that this sorption relationship applies only at a constant temperature. 

For dilute non-reacting solutions, Henry s Law is used to describe the linear equilibrium distribution of a compound between the bulk liquid and gas phases (Figure 3-3) ... 

In what follows we shall assume that x. .. may be taken as zero. We have already studied in chap. XVIII, 3 and 4, the equilibrium distribution of a component between one phase consisting of a pure compound, and a second phase consisting of a solution. 

A phenomenon of concentration of a substance on the interface is called adsorption. Surface activity is due to the unequal distribution of a solute between the surface and the bulk solution. Quantitative description of the adsorption of a solute at gas-liquid interfaces, under an equilibrium condition, is expressed by the Gibbs adsorption equation as... 

The discussion in this section has been concerned with the distribution of a solute between two liquid, phases whose equilibrium is unaffected by the added solute. This will occur if the amount of added solute is very small, or if the solvents are essentially immiscible at all conditions. However, if the amount of dissolved solute is so large as to affect the miscibility of the solvents, the solute addition can have a significant effect on the solvents, including the increase (salting in) or decrease (saltin out) of the mutual solubility of the two solvents, as was discussed in Sec. 11.2. It is important to emphasize that such situations are described by the methods in Sec. 11.2 as a multicomponent liquid-liquid equilibrium problem, in contrast to the procedures in this section, which are based on the assumption that the partial or complete immiscibility of the solvents is imaffected by the addition of the partitioning solute. 

To be suitable for commercial applications, a sorbent should have a high selectivity to enable sharp separations, high capacity to minimize the amount of sorbent needed, and the capability of being regenerated for reuse. These properties depend upon the dynamic equilibrium distribution of the solute between the fluid and the solid surface. Unlike vapor-liquid and liquid-liquid equilibria where theory is often applied to estimate phase distribution of the solute, no acceptable theory has been developed to predict solid-sorbent equilibria. Thus, it is necessary to obtain... 

Distrihution ratio, equilibrium constant K, the term describing the distribution of a solute between the mobile phase and stationary phase and reflects the retention forces. Also known as partition ratio Kp, for partition chromatography. 

Partition coefficient, describes the distribution of a solute between a liquid or gaseous mobile phase and a liquid stationary phase on an inert support material. The solute molecules are partitioned between the two phases according to the retention forces of the stationary phase and the solvating properties of the mobile phase in LC or vapour pressure in GC. The equilibrium is temperature dependent see distribution ratio ... 

Shaking Separatory Fuimels. A separatory funnel and its contents should be shaken to mix the immiscible liquids as intimately as possible (Fig. 2.61b). The shaking process increases the surface area of contact between the immiscible liquids so that the equilibrium distribution of the solute between the two layers will be attained quickly however, overly vigorous or lengthy shaking may produce emulsions (discussed below). 

In Section 3.3, we illustrated the thermodynamic relations that govern the conditions of equilibrium distribution of a species between two or more immiscible phases under thermodynamic equilibrium. In Section 4.1, we focus on the value of the separation factor or other separation indices for two or more species present in a variety of two-phase separation systems under thermodynamic equilibrium in a closed vessel. The closed vessels of Figure 1.1.2 are appropriate for such equilibrium separation calculations. There is no bulk or diffusive flow into or out of the system in the closed vessel. The processes achieving such separations are called equilibrium separation processes. Separations based on such phenomena in an open vessel with bulk flow in and out are studied in Chapters 6, 7 and 8. No chemical reactions are considered here however, partitioning between a bulk fluid phase and an individual molecule/macromolecule or collection of molecules for noncovalent solute binding has been touched upon here. The effects of chemical reactions are treated in Chapter 5. Partitioning of one species between two phases is an important aspect ever present in this section. 

Although less pronounced than the effect on gases, pressure can have a considerable effect on the physical chemistry of liquids. Pressure can influence many of the physical attributes of the mobile phase such as melting point or boiling point, density, and viscosity. In addition, the attributes of a compound in solution can also be somewhat influenced by pressure, for example, diffusion coefficient. The distribution of a solute between solid stationary phase and liquid mobile phase can also be affected by pressure, for example, equilibrium constant and phase ratio. 

The currently most useful approximations of trace element behavior for quantitative prediction are based on a simple Nernst distribution for equilibrium partitioning of a solute between two phases. This concept can be formalized to account for exchange between the trace element and the major ion it is deemed to replace, to account for effects of compensation of charge, etc. (e.g., Mclntire,... 

In many practical situations solute A may dissociate, polymerize or form complexes with some other component of the sample or interact with one of the solvents. In these circumstances the value of KD does not reflect the overall distribution of the solute between the two phases as it refers only to the distributing species. Analytically, the total amount of solute present in each phase at equilibrium is of prime importance, and the extraction process is therefore better discussed in terms of the distribution ratio D where... 

When a solute is added to one of the two solutions, it will difFuse into the other, and after a certain time equilibrium will be established. The distribution of the solute between the two phases is known as partitioning, and can be determined from standard thermodynamics. 

The equilibrium distribution of a volatile solute between gas and liquid phases is described by Henry s law. For the equilibrium A(l) = A(g) in a dilute solution at low gas pressure,... 

Consider a two-phase system with components AY and BY in which some of the BY(s) becomes dissolved in AY(s) BY is the solute and AY the solvent. If the resulting solid solution is homogeneous, that is, it contains no concentration gradient, the equilibrium distribution of A and B between the liquid and solid is... 

The distribution ratio of a solute between two liquid phases at equilibrium is a constant, provided that the solute forms a dilute ideal solution in each phase. 

T he partitioning of a solute between the stationary and mobile phases of a gel permeation column is a function of the molecular size and shape of the solute and the size distribution of gel pores separating the two phases. For a gel permeation column operating under conditions in which an equilibrium distribution of solute between the phases is ob-... 

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