Nernsts Distribution Law

Nernst Distribution Law Any neutral species will ilistribute between two iniscible solvents such that the ratio of the concentrations remains a constant. 

A review of several classic equilibrium equations is in order. The Nernst distribution law states that a neutral species will distribute between two immiscible solvents with a constant ratio of concentrations. 

The behavioural pattern of two immiscible solvents, say a and ib is essentially nonideal with respect to one another. Now, if a third substance is made to dissolve in a two-phase mixture of the solvents (i.e., a and 3 ), it may behave ideally in either phases provided its concentration in each individual phase is approximately small. Therefore, under these prevailing experimental parameters the ratio of the mole fractions of the solute in the two respective immiscible phases ( a and A) is found to be a constant which is absolutely independent of the quantity of solute present. It is termed as the Nernst Distribution Law or the Partition Law and may be expressed as follows ... 

If the solute A does not undergo any reaction in the two solvents, except for the solubility caused by the solvation due to the nonspecific cohesive forces in the liquids, the distribution of the solute follows the Nernst distribution law, and the equilibrium reaction can be described either by a distribution constant or an (equilibrium) extraction constant... 

Analytes distribute themselves between aqueous and organic layers according to the Nernst distribution law, where the distribution coefficient, Kq. is equal to the analyte ratio in each phase at equilibrium. 

When a liquid is extracted by a solid, phase A of the Nernst distribution law [equation (2.2)] refers to the liquid sample, and phase B, the extracting phase, represents the solid (or solid-supported liquid) phase ... 

Discuss whether the Nernst Distribution Law holds for this system. (b) For the distribution of benzoic acid in water and benzene, the following data have been reported at 20°C CH,o(g/100 cc) 0.289 0.1952 0.1500 0.0976 0.0788... 

Check whether the Nernst Distribution Law applies. If not, what changes are needed to obtain a constant distribution coefficient What does this imply about the solution process of benzoic acid in the two phases ... 

The relation Rpx = P"/x[ is simply a reformulation of Raoult Law when applied to the solvent. Any of the other relations are equivalent to Henry s Law when applied to the solute. Rxx = x [ x[ is also known as the Nernst Distribution Law. 

If we set the affinity equal to zero we obtain the general form of the Nernst distribution law (7.42) ... 

The equilibrium constant Ki(T,p), which is independent of mole fraction is called the distribution or partition coefficient of the substance i between the solutions 1 and 2. This equation is the generalized form of the Nernst distribution law. 

Prove that if a solute is distributed between two immiscible solvents (I and II), the ratio of the activities in the two solvents, i.e., ai/an, should be constant at constant temperature and pressure. Show that this result is the basis of the Nernst distribution law, i.e., ci/cii (or mi/mn) is constant for dilute solutions. 

A detailed description of this experiment and other comparable experiments for demonstrating the Nernst distribution law have recently been published by Elias et al. ... 

DYNAMICS OF DISTRIBUTION The natural aqueous system is a complex multiphase system which contains dissolved chemicals as well as suspended solids. The metals present in such a system are likely to distribute themselves between the various components of the solid phase and the liquid phase. Such a distribution may attain (a) a true equilibrium or (b) follow a steady state condition. If an element in a system has attained a true equilibrium, the ratio of element concentrations in two phases (solid/liquid), in principle, must remain unchanged at any given temperature. The mathematical relation of metal concentrations in these two phases is governed by the Nernst distribution law (41) commonly called the partition coefficient (1 ) and is defined as = s) /a(l) where a(s) is the activity of metal ions associated with the solid phase and a( ) is the activity of metal ions associated with the liquid phase (dissolved). This behavior of element is a direct consequence of the dynamics of ionic distribution in a multiphase system. For dilute solution, which generally obeys Raoult s law (41) activity (a) of a metal ion can be substituted by its concentration, (c) moles L l or moles Kg i. This ratio (Kd) serves as a comparison for relative affinity of metal ions for various components-exchangeable, carbonate, oxide, organic-of the solid phase. Chemical potential which is a function of several variables controls the numerical values of Kd (41). 

Thus if the solute follows Henry s Law in both phases the ratio of its concentrations in the phases will be constant. This result is sometimes referred to as the Nernst Distribution Law. 

The equilibrium curve can often be described by the Nernst distribution law (Equation 2.3.4-3), but because of the concentration dependence it must often be determined experimentally ... 

This extraction of organic solutes, such as drug substances from biological samples, occurs based on the Nernst distribution law, sometimes known... 

For further information on Gibbs s phase rule, see Elements of Physical Chemistry in the Further Reading section at the end of this chapter. According to the Nernst distribution law. 

Molecule The smallest part of a substance that is composed of two or more atoms of the same or different type held together by chemical forces Nernst distribution law (partition law) The ratio (constant) at which an analyte will become distributed between two immiscible solvents at... 

For a substance S distributed in phase I (raffinate R) and phase II (ertract E) with a small concentration of Cj i and Cj n the Nernst Distribution Law is an approximation given by... 

For separation by liquid-liquid extraction, the Nernst distribution law describes the equilibrium between raffinate and extract phases if the carrier component T and solvent component L are not miscible (see Chapter 6). 

Table 1-6 shows additional variations of the Nernst distribution law. 

Table 1-6. Additional formulae of the Nernst distribution law. Correlations and conversion relationships for the distribution coefficient K.

The loading capacity of the key component, or pollutant, to be transferred to the solvent gives the distribution of the component between the two liquid phases. This distribution equilibrium is described by the Nernst distribution law (Chapter 1.4.2.1). The amount of circulated solvent is a function of the loading capacity. The selectivity characterizes how much better the key component is extracted than the other components. The higher the selectivity of a solvent, the lower the number of separation stages required in the extractor. 

It is also possible to derive the Nernst distribution law from thermodynamic considerations using the concept of free energy (Lewis and Randall 1923). At equilibrium, the chemical potential of a solute X has to be the same in the aqueous and the organic phase, i.e.. 

Nernst distribution law is stated as - when a solute distributes itself between two non-miscible solvents in contact with each other, there exists for similar molecular species at a constant temperature, a constant ratio of distribution between the two solvents irrespective of the amounts of the solute and the liquids. 

The separation of components in gas chromatographic processes is the result of equilibrium distribution between a mobile gas phase and a liquid or solid stationary phase. The partition of a component between two phases is described by the Nernst distribution law. 

The Nernst distribution law applies to metal complexes, but their distribution ratios are determined by several interrelated equilibria. As in the case of organic acids and bases, the efficiency of extraction of metal chelates is pH dependent, and for some ion-association complexes, notably oxonium systems (hydrogen ions solvated with ethers, esters or ketones), inorganic complex ions can be extracted from concentrated solutions of mineral acids. 

Nernst distribution law constant Boiling point elevation constant Freezing point depression constant Equilibrium constant Acid ionization constant Michaelis-Menten constant... 

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