Constant solubility

In Section 8, the material on solubility constants has been doubled to 550 entries. Sections on proton transfer reactions, including some at various temperatures, formation constants of metal complexes with organic and inorganic ligands, buffer solutions of all types, reference electrodes, indicators, and electrode potentials are retained with some revisions. The material on conductances has been revised and expanded, particularly in the table on limiting equivalent ionic conductances. 

The calcium phosphate solubility constant [KCa3(P04)2] is extremely small and phosphate quickly reacts with calcium when present in warm to hot, alkaline BW in the ortho- form. This reaction is complete and superior to the soda ash precipitation reaction. In addition, calcium phosphate is stable and does not decompose. 

K,p is also called the solubility product constant and, most simply, the solubility constant. 

Solubility equilibria are described quantitatively by the equilibrium constant for solid dissolution, Ksp (the solubility product). Formally, this equilibrium constant should be written as the activity of the products divided by that of the reactants, including the solid. However, since the activity of any pure solid is defined as 1.0, the solid is commonly left out of the equilibrium constant expression. The activity of the solid is important in natural systems where the solids are frequently not pure, but are mixtures. In such a case, the activity of a solid component that forms part of an "ideal" solid solution is defined as its mole fraction in the solid phase. Empirically, it appears that most solid solutions are far from ideal, with the dilute component having an activity considerably greater than its mole fraction. Nevertheless, the point remains that not all solid components found in an aquatic system have unit activity, and thus their solubility will be less than that defined by the solubility constant in its conventional form. 

While the solubility constants for various potential solids can indicate which solid is thermodynamically stable under a given set of conditions, reactions involving precipitation or dissolution of a solid are typically more subject to kinetic limitations than are reactions that take... 

Wakita, K., Yoshimota, M., Miyamoto, S., Watanabe, H. A method for calculation of the aqueous solubility of organic compounds by using new fragment solubility constants. Chem. Pharm. Bull. 1986, 34, 4663 681. 

In an ideally designed experiment, only a single titration is needed to determine the solubility constant and the aqueous pKa. This is possible when the amount of sample, such as a weak base, added to solution is such that from the start of an alkalimetric titration (pH [Pg.104]

Such a reaction can cause a shift in the apparent ionization constant. It was discovered that the A shift, when subtracted from the logarithm of the apparent (DMSO-distorted) solubility, S ( )PP, yields the true aqueous solubility constant ... 

Table 6.3 Solubility Constants of Drug Molecules, Measured by the Dissolution Template Titration Method3...

Table 6.3 lists a set of reliably determined log So solubility constants for a series of ionizable drugs determined by the pH-metric DTT solubility method. 

Feitknecht, W. Schindler, P, Solubility Constant of Metal Oxides, Metal Hydroxides and Metal Hydroxide Salts in Aqueous Solution, Butterworths, London, 1963. 

The concentration of a compound in water is controlled by its equilibrium solubility or solubility constant (the maximum amount of a compound that will dissolve in a solution at a specified temperature and pressure). Equilibrium solubility will change with environmental parameters such as temperature, pressure, and pH for example, the solubility of most organic compounds triples when temperature rises from 0°C to 30°C. Each type of waste has a specific equilibrium solubility at a given temperature and pressure. The solubility of toxic organic compounds is generally much lower than that of inorganic salts. This characteristic is particularly true of nonpolar compounds because of their hydrophobic character. 

The permeation technique is another commonly employed method for determining the mutual diffusion coefficient of a polymer-penetrant system. This technique involves a diffusion apparatus with the polymer membrane placed between two chambers. At time zero, the reservoir chamber is filled with the penetrant at a constant activity while the receptor chamber is maintained at zero activity. Therefore, the upstream surface of the polymer membrane is maintained at a concentration of c f. It is noted that c f is the concentration within the polymer surface layer, and this concentration can be related to the bulk concentration or vapor pressure through a partition coefficient or solubility constant. The amount... 

Dupont et al. [60] studied the same reaction, but used [BMIM][PF6] and [BMIM][BF4] as ionic liquids. A special focus of their investigations was on the influence of H2-pressure on conversion. The Henry coefficient solubility constant was determined by pressure drop experiment in a reactor, which is a known procedure to measure gas solubilities [93]. The values reported by these authors were FC=3.0xl0-3 mol IT1 atm1 for [BMIM][BF4]/H2 and 8.8x10 4 mol L 1 atm-1 for [BMIM][PF6]/H2 at room temperature, which differ significantly from those determined by the 1H-NMR technique (see Table 41.2) [59]. However, their values indicated that molecular hydrogen is almost four times more soluble in [BMIM][BF4] than in [BMIM][PF6] under the same pressure. According to the authors, this is reflected by the values of conversion (ee), which were 73% (93% ee) for [BMIM][BF4] and 26% (81% ee) for [BMIM][PF6] at 50 bar H2 pressure (Table 41.9, entries 2 and 4). 

An alternative way of expressing the partition constant of a sparingly soluble salt is to define its solubility product Rsp (also called the solubility constant Rs). Ks is defined as the product of the ion activities of an ionic solute in its saturated solution, each raised to its stoichiometric number v . Ks is expressed with due reference to the dissociation equilibria involved and the ions present. 

Schindler and his coworkers determined the solubility constants and the influence of molar surface, S, upon solubility (25° C)... 

Although conductimetry is useful in determining various physical constants, e.g. dissociation and solubility constants, its major analytical application is for monitoring titrations. 

Table VI. Effect of Pressure on Gas Solubility (Constant Temperature) ...

To leam how the solubility constant, AT, can be measured potentiometri-cally. 

Some ionic salts dissolve only imperceptibly, e.g. 10 -10 mol dm . A simple measure of how much material actually enters solution is the solubility constant (also called the solubility product, and sometimes given the symbol Tsp)- An expression for may be formulated simply by multiplying the activity... 

Electroanalysis is a powerful means of obtaining solubility constants for solutes in which the amount of one or more of the ions can be determined electrochemically. To obtain a(ion), we will either employ an ISE or perform a calculation with the Nemst equation. 

A major part of this chapter considered the ways used to calculate concentrations or activities by using variants of the Nemst equation. For example, we saw how the solubility constant Ks can be measured potentiometrically. 

To learn that the solubility constants (products), of sparingly soluble salts can be obtained from a potentiometric titration the activity of one constituent ion is determined directly from the emf at the end point, and the salt stoichiometry then allows to be calculated. 

Figure 4.9 Gran plot of electrode potential E against volume of silver ion (O), used to determine the solubility constant of AgCl. E is obtained from the emf of the cell, reference electrode Ag ISE , where the ion-selective electrode is a solid-state ISE based on AgjS. The ISE is immersed in a stirred solution of KCl (of initial concentration 5 X 10 mol dm ) the volume values on the jc-axis relate to the aliquots of added AgN03 (of concentration 2 x 10 mol dm ). The antilog trace ( ) is clearly proportional to the volume of AgNOs added. From Christian, G.D., Analytical Chemistry, 5th Edn, Wiley, 1994. Reprinted by permission of John Wiley Sons, Inc.

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