Slightly soluble substance

Destructive solid sample preparation methods, such as digestion and mineralisation, are well known as they have been around for some time they are relatively cheap and well documented [13-15]. Decomposition of a substance or a mixture of substances does not refer so much to the dissolution, but rather to the conversion of slightly soluble substances into acid- or water-soluble (ionogenic) compounds (chemical dissolution). 

Efflorescence. The solvent properties of water also causes efflorescence, a phenomenon whereby soluble or slightly soluble substances migrate from the interior of porous solids to the surface, where they precipitate. Efflorescence is an important factor in the decay and disintegration of many rocks, and of human-made porous materials such as ceramics, and even of some types of glass. On archaeological objects, efflorescence generally occurs mostly as a white, powdery, but sometimes consolidated accretion on the surface of the objects. Calcite, a form of calcium carbonate, is one of the most common substances to effloresce on archaeological ceramics. 

Lead chloride (PbCl2) is the most soluble, next is silver chloride (AgCl), and the least soluble is mercury I chloride (Hg2Cl2). Solubility of slightly soluble substances can be determined from Ksp values. 

As shown in Equation (2.164b), the solubility of slightly soluble substances is simply related to the solubility product (Ksp). However, the solubility is dependent on the ionic strength of a solution. A slightly soluble salt dissolves in water ... 

In the method developed by Exerowa, Cohen and Nikolova [144] the insoluble (or slightly soluble) monolayers are obtained by adsorption from the gas phase. A special device (Fig. 2.28) was constructed for the purpose a ring a in the measuring cell of Scheludko and Exerowa for formation of microscopic foam films at constant capillary pressure (see Section 2.1.2.). The insoluble (or slightly soluble) substance from reversoir b is placed in this ring. Conditions for the adsorption of the surfactant on either surface of the bi-concave drop are created in the closed space of the measuring cell. The surfactant used was n-decanol which at temperatures lower than 10°C forms a condensed monolayer. Thus, it is possible to obtain common thin as well as black foam films. The results from these studies can be seen in Section 3.4.3.3. 

This process of solution of a slightly soluble substance through formation of a complex by one of its ions is the basis of some of the most important practical applications of complex formation. Several examples are mentioned later in this chapter. 

In accurate calculations employing activity coefficients, the total ionic strength for all solutes, including the contribution of the slightly soluble substance, determines the solubility (Section 2-6). 

Dissociation of water Heterogeneous equilibrium between a slightly soluble substance and its ions in a saturated solution... 

Such a solution is said to be saturated. Saturation occurs at very low concentrations of dissolved species for slightly soluble substances and at high concentrations for very soluble substances. When imperfect crystals are placed in saturated solutions of their ions, surface defects on the crystals are slowly patched with no net increase in mass of the solid. Often, after some time has passed, we see fewer but larger crystals. These observations provide evidence of the dynamic nature of the solubility equilibrium. After equilibrium is established, no more solid dissolves without the simultaneous crystallization of an equal mass of dissolved ions. 

Determination, by Conductance Measurements, of the Solubilities of Slightly Soluble Substances, The solubilities of slightly soluble salts can, in many cases, be obtained from determinations of the specific conductance, l, of their saturated solutions. The calculation involves equation (8a) of Chapter 3, which, for this case, may be put in the form... 

Reagent immobilisation is generally accomplished by using slightly soluble substances or by anchoring specific chemical species on a solid support. 

Another type of eqnilibrinm, which we will consider in the second half of this chapter, involves the dissolution and precipitation of slightly soluble substances. These processes are examples of heterogeneous equilibria—that is, they pertain to reactions in which the components are in more than one phase. 

In Chapter 16 we discussed the solubility product of slightly soluble substances. Using the solubility product of silver chloride at 25°C (1.6 X 10 °), calculate AG° for the process... 

Solubility has been established as a factor in adsorption, but it is important to recognize the true nature of its influence, which is that of a restraining force—a brake against the pull of the carbon. Even great solubility, however, does not prevent the adsorption of a substance that is strongly attracted to the carbon surface, e.g., the very soluble chloroacetic acid is well adsorbed. Conversely, a slightly soluble substance will be adsorbed only if and when an attraction exists for the carbon. A correlation with solubility is more clearly defined when comparing similar molecular structures, but even here the relation is sometimes absent. 

The mechanism involved can be illustrated by citing a common producer of haze, namely a supersaturated solution of a slightly soluble substance. When organic colloids are present in such a system, precipitation is retarded or even prevented but if and when it does occur, the precipitation is seldom complete and some degree of supersaturation still remains in solution. 

External mass transfer, such as diffusion to particles or to the outside of pipes or cylinders, requires different correlations from those for internal mass transfer, because there is boundary-layer flow over part of the surface, and boundary-layer separation is common. The mass-transfer coefficients can be determined by studying evaporation of liquid from porous wet solids. However, it is not easy to ensure that there is no effect of internal mass-transfer resistance. Complications from diffusion in the solid are eliminated if the solid is made from a slightly soluble substance that dissolves in the liquid or sublimes into a gas. This method also permits measurement of local mass-transfer coefficients for different points on the solid particle or cylinder. 

A weak electtolyte is only partially dissociated. A slightly soluble substance is a strong electrolyte because the portion that dissolves is totally ionized. 

When a substance dissolves in water, it will often partially or completely dissociate or ionize. Partially dissociated electrolytes are called weak electrolytes, and completely dissociated ones are strong electrolytes. For example, acetic acid only partially ionizes in water and is therefore a weak electrolyte. But hydrochloric acid is completely ionized and thus is a strong electrolyte. (Acid dissociations in water are really proton transfer reactions HOAc + H2O HsO + OAc ). Some substances completely ionize in water but have limited solubility we call these slightly soluble substances. Substances may combine in solution to form a dissociable product, for example, a complex. An example is the reaction of copper(II) with ammonia to form the CulNHs)/ species. 

The dissociation of weak electrolytes or the solubility of slightly soluble substances can be quantitatively described by equilibrium constants. Equilibrium constants for completely dissolved and dissociated electrolytes are effectively infinite. Consider the dissociating species AB ... 

Kohler theory was originally developed for inorganic salt solutes and, as in Section 17.2.5, can be readily adapted to an insoluble substance as well. Recently Kohler theory has been extended to soluble trace gases, slightly soluble substances, and solutes that... 

A.2 Modified Form of the Kohler Theory for a Slightly Soluble Substance... 

Thus, we write the concentration of the slightly soluble substance in the aqueous phase Css as... 

This expression is similar to (17.A.22) except for the new final term that accounts for the extra solute effect from the slightly soluble substance, and all terms involving of D p in (17.A.22) are replaced by (D — reflecting the subtracted volume owing to the... 

Laaksonen, A., Korhonen, P., Kulmala, M., and Charlson, R. J. (1998) Modification of the Kohler equation to include soluble trace gases and slightly soluble substances, J. Atmos. Sci. 55, 853-862. 

The presence of the slightly soluble substance changes the electrode system from one whose potential responds to changes in the activity of metal ion to one whose potential depends on the activity of another ion. These are called electrodes of the second kind. It is of analytical importance to be able to follow changes in ajj+ (for example, in pH measurements) or a f by means of these or similar electrode systems. 

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