Principle of solubility product

The principle of solubility product is the major factor in governing the gravimetric analysis. Justify the statement adequately with appropriate examples. 

The industrial process by which large quantities of sodium hydroxide are made consists in treating a 10 per cent solution of sodium carbonate with an excess of calcium hydroxide (milk of lime). After the reaction is complete the mixture is filtered to remove the precipitated calcium carbonate and excess of calcium hydroxide. This process involves a most important application of the principle of solubility product calcium hydroxide continues to dissolve and calcium carbonate to precipitate according to the reaction... 

This reaction, combined with subsequent leaching of the bicarbonate salts from the soil surface, slowly depletes the carbonate buffering capacity of the soil, and ultimately the soil pH may be lowered. However, the carbonate buffer capacity of many calcareous soils is so large that it would take centuries of acid inputs (natural and anthropogenic) to have any effect on pH. From the principle of solubility products, these carbonates must be completely dissolved out of the soil before the pH can drop. 

Solubility product principle The solubility product constant expression for a slightly soluble compound is the product of the concentrations of the constituent ions, each raised to the power that corresponds to the number of ions in one formula unit. 

The principle of cheese production by ultrafiltration is that the proteins are concentrated by UF in the soluble form, i.e. before the enzyme treatment. The concentration is controlled in such a way that the composition of the concentrate as regards fat, protein, salts and water, is equivalent to the composition of the finished cheese. It is at this point the enzyme is added, causing the cheese to set in the form, into which it has been poured. The whey proteins, which were previously wasted during the traditional process, remain in the finished cheese, resulting in increased production and therefore higher profits. I shall revert to this later. 

Unfortunately, like all easy to use principles, the solubility product principle is not generally applicable. At higher concentrations, electrical interactions, complex formation, and solution nonideality make the prediction of the effect of ionic species on the solubility of other ionic species much more complicated. 

In principle it is possible to use ffie Kgp value of a salt to calculate solubility rmder a variety of conditions. In practice, great care must be taken in doing so for the reasons indicated in "A Closer Look" on the limitations of solubility products in Section 17.5. Agreement between measured solubility and that calculated from Kgp is usually best for salts whose ions have low charges (1+ and 1—) and do not hydrolyze. Figure 17.14 summarizes the relationships among various expressions of solubility and Kgp. 

The solubility product principle is generally valid only for saturated solutions in which the total concentration of ions of the slightly soluble compound is no more than about 0.01 M. Compounds with a less than lO" have extremely low solubility. Examine the table of solubility product constants in Appendix H. Which compound appears to be the most soluble Calculate its molar solubility. Which compound appears to be the least soluble Calculate its molar solubility. 

Kittrick, J. A., and M. L. Jackson, 1955. Application of solubility product principles to the variscite-kaolinite system. Proc. Soil Sci. Soc. Am. 19 455. 

In reaction (7), all of the molecular species involved in the equilibrium are in the solution as dissolved species. Though the equilibrium relationship that exists among the concentrations is a little more complicated than in the solubility product expressions, the guiding principles are the same. 

In a catalytic asymmetric reaction, a small amount of an enantio-merically pure catalyst, either an enzyme or a synthetic, soluble transition metal complex, is used to produce large quantities of an optically active compound from a precursor that may be chiral or achiral. In recent years, synthetic chemists have developed numerous catalytic asymmetric reaction processes that transform prochiral substrates into chiral products with impressive margins of enantio-selectivity, feats that were once the exclusive domain of enzymes.56 These developments have had an enormous impact on academic and industrial organic synthesis. In the pharmaceutical industry, where there is a great emphasis on the production of enantiomeri-cally pure compounds, effective catalytic asymmetric reactions are particularly valuable because one molecule of an enantiomerically pure catalyst can, in principle, direct the stereoselective formation of millions of chiral product molecules. Such reactions are thus highly productive and economical, and, when applicable, they make the wasteful practice of racemate resolution obsolete. 

An important application of the solubility product principle is to the calculation of the solubility of sparingly soluble salts in solutions of salts with a common... 

Factor 1, which is concerned with the completeness of precipitation, has already been dealt with in connection with the solubility-product principle, and the influence upon the solubility of the precipitate of (i) a salt with a common ion, (ii) salts with no common ion, (iii) acids and bases, and (iv) temperature (Sections 2.6-2.11). 

It must be pointed out that the above calculation is approximate only, and may be regarded merely as an illustration of the principles involved in considering the precipitation of sulphides under various experimental conditions the solubility products of most metallic sulphides are not known with any great accuracy. It is by no means certain that the sulphide ion S 2 is the most important reactant in acidified solutions it may well be that in many cases the active precipitant is the hydrogensulphide ion HS , the concentration of which is considerable, and that intermediate products are formed. Also much co-precipitation and post-precipitation occur in sulphide precipitations unless the experimental conditions are rigorously controlled. 

The silver ions involved are derived from the silver chloride, and by the solubility product principle (Section 2.6), the activity of these ions will be governed by the chloride-ion activity... 

Like many other antibodies, the activity of antibody 14D9 is sufficient for preparative application, yet it remains modest when compared to that of enzymes. The protein is relatively difficult to produce, although a recombinant format as a fusion vdth the NusA protein was found to provide the antibody in soluble form with good activity [20]. It should be mentioned that aldolase catalytic antibodies operating by an enamine mechanism, obtained by the principle of reactive immunization mentioned above [15], represent another example of enantioselective antibodies, which have proven to be preparatively useful in organic synthesis [21]. One such aldolase antibody, antibody 38C2, is commercially available and provides a useful alternative to natural aldolases to prepare a variety of enantiomerically pure aldol products, which are otherwise difficult to prepare, allovdng applications in natural product synthesis [22]. 

Intelligent engineering can drastically improve process selectivity (see Sharma, 1988, 1990) as illustrated in Chapter 4 of this book. A combination of reaction with an appropriate separation operation is the first option if the reaction is limited by chemical equilibrium. In such combinations one product is removed from the reaction zone continuously, allowing for a higher conversion of raw materials. Extractive reactions involve the addition of a second liquid phase, in which the product is better soluble than the reactants, to the reaction zone. Thus, the product is withdrawn from the reactive phase shifting the reaction mixture to product(s). The same principle can be realized if an additive is introduced into the reaction zone that causes precipitation of the desired product. A combination of reaction with distillation in a single column allows the removal of volatile products from the reaction zone that is then realized in the (fractional) distillation zone. Finally, reaction can be combined with filtration. A typical example of the latter system is the application of catalytic membranes. In all these cases, withdrawal of the product shifts the equilibrium mixture to the product. 

The solubility product principle states that the solubility product expression for a slightly soluble compound is the product of the concentrations of its constituent ions, each raised to the power that corresponds to the number of ions in one formula unit of the compound. The quantity, K, is constant at constant temperature for a saturated solution of the compound, when the system is at equilibrium. The significance of the solubility product is that it can be used to calculate the concentrations of the ions in solutions for such slightly soluble compounds. 

The common-ion effect is an application of Le Chatelicr s principle to equilibrium systems of slightly soluble salts. A buffer is a solution that resists a change in pH if we add an acid or base. We can calculate the pH of a buffer using the Henderson-Hasselbalch equation. We use titrations to determine the concentration of an acid or base solution. We can represent solubility equilibria by the solubility product constant expression, Ksp. We can use the concepts associated with weak acids and bases to calculate the pH at any point during a titration. 

The principle of differential solubility is also applied conversely, namely, when the by-product can be separated from the just-satur-ated solution of the substance because of its low solubility in an appropriate solvent. Since, in this case, the solution always remains saturated with respect to the by-product, it is never possible by this method to obtain a substance in one operation, as may be possible by the first method. 

A different application of visible microscopy was pioneered by Gomori. In 1941 he showed that alkaline phosphatase could be specifically located by its hydrolysis of soluble phosphate esters (initially glycerophosphate). If calcium ions were present in the medium in which the sections were incubated, insoluble calcium phosphate precipitated as a result of the action of the hydrolase. The site of the precipitate could be visualized if cobalt or lead salts were subsequently added to replace calcium and the sections exposed to hydrogen sulfide. In principle many hydrolases and other enzymes could be studied using the appropriate substrates and precipitants. It was important to ensure that the products of the enzyme reactions did not diffuse from the sites where the enzymes were located. It was also essential that the reagents could reach the enzyme site. 

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