THE CONCEPT OF SOLUBILITY

Solubility of a substance is defined as the amount of the substance that will dissolve in a particular solvent. Let s consider an example in which sucrose is added to water. When we add sucrose and stir, it dissolves in the water. Let s say we keep on adding more and more sucrose to the solution. Since more and more sucrose is dissolving, the solution is not saturated or it is called an unsaturated solution. 

It reaches a point where additional amount of sucrose will not dissolve in that solution. At that point the solution is said to be saturated. We have yet another category in this tradition of categorizing solutions. In some cases, certain solutes become more soluble if the solution is heated. Such solutions are called supersaturated solutions. If we carefully and slowly cool down a supersaturated solution without disturbing its contents, normally we will still have a supersaturated solution. At this stage, even the slightest addition of the solute will result in crystallization. 

---

Once the concept of solubility is understood, students look at animations that show two solutions being mixed resulting in the exchange of ions and formation of an insoluble compound (see the screen captures in Figs. 6.2, 6.3 and 6.4). Students generally do not consider how precipitates are formed, so the animation showing how the ions (at the sub-microscopic level) attract each other and aggregate to form a precipitate (at the macroscopic level) will help them to understand the interactions of the ions involved. 

Finally, first attempts were made to extend the concept of soluble hyperbranched polymers to dendronized sohd-phase materials. Recently, the first dendronized sohd phase, accessible in only one reaction step was reported (Fig. 7.4) [36]. The coupling of hyperbranched polyglycerol to Merrifield resin yields a new type of high-loading sohd-phase hybrid material with loading capacities of ca. 3 mmol g and good swelling properties even in protic solvents (see also Section 3.4). 

To overcome this issue Kureshy et al. [55, 56] reported dimeric form of Jacobsen s catalysts 3, 4. They used the concept of solubility modification by altering the molecular weight of the catalyst so that in a post catalytic work-up procedure the catalyst is precipitated, filtered and used for subsequent catalytic runs. The complexes 3, 4 (0.2 mol % of Co(lll)-salen unit) (Figure 2) were effectively used for HKR of racemic epoxides, e.g., styrene oxide, epichlorohydrin, 1,2-epoxypropane, 1,2-epoxyhexane, 1,2-epoxyoctane, and 1,2-epoxydodecane to achieve corresponding epoxides and 1,2-diols in high optical purity and isolated yields. In this process, once the catalytic reaction is complete the product epoxides were collected by reduced pressure distillation. Addition of diethylether to the residue precipitated the catalyst which was removed by filtration. However, the recovered catalyst was required to be reactivated by its treatment with acetic acid in air. The catalysts were reused 4 times with complete retention of its performance. 

Thus the expression solubility of nitrocellulose in a certain solvent has a different meaning from the concept of solubility as applied to a crystalline substance able to form a saturated solution. 

The properties of the stationary phase manifest themselves in the activity coefficient in eqn.(3.6). A very simple expression for the activity coefficient can be obtained from the concept of solubility parameters (see section 2.3.1). This expression can be seen as a special form of Hildebrand s regular mixing rule, and it reads [303]. 

In Eq. (2), R is the universal gas constant and T is the absolute temperature in degrees Kelvin. The concept of solubility parameter can be used to predict the partition coefficient qualitatively in the selection of solvents.22 We can write K as... 

Flory, P. J. "Principles of Polymer Chemistry" Cornell Unlv. Press Ithaca, N.Y. 1953. (The concept of solubility parameters is not explicitly referred to in this book, but the concomitant regular solution concept is employed.)... 

While the concept of solubility parameter has a physical basis, it is essentially an empirical parameter that may be related to the Flory-Huggins parameter. As such it has value in understanding polymer blends in that the conditions for phase separation may be rationalized. 

The concept of solubility parameters is an attempt to quantify the old rule-of-thumb, like dissolves like. It must of necessity fail when the interaction forces differ greatly in nature. Recently the solubility parameter has been separated into three component parameters in order to refine the quite crude process of trying to predict the possible mixability of a polymer and a solvent. The three components describe the interaction between dispersion, dipole, and hydrogen-bonding forces ... 

The ideas of Burrell have been extended by others to make their use more quantitatively precise. Unfortunately, these extensions almost invariably make the concept of solubility parameters more difficult to use in practice. The simple initial concept of Burrell outlined above is still a very useful one for the paint chemist and technologist. 

Bonding The use of solvents (mostly with a cement made of a viscous solution of the same polymer) is common for easily soluble amorphous polymers like acrylics, polystyrene, cellulose, and PVC. However, this method does not apply to most crystalline polymers. The proper choice of solvent (or mixture of solvents) also takes into account the desired rate of diffusion. In this matter, the concept of solubility parameters may be exploited when there is a similarity between polymer and solvent. Various glues may also be used (contact glue, epoxy) in order to bind plastics to each other, including crystalline polymers or thermosets. 

The thermodynamic affinity between components of a solution is important for quantitative estimation of mutual solubility. The concept of solubility parameters is based on enthalpy of the interaction between solvent and polymer. Solubility parameter is the square root of the cohesive energy density, CED ... 

Despite restrictions, the theory of regular solutions and the concept of solubility parameters is convenient in practical applications. ... 

Thus, for a priori evaluation of plasticizer s effectiveness in decreasing the glass transition temperature of a polymer, it is desirable to estimate the thermodynamic compatibility of a polymer and a plasticizer using, for example, the concept of solubility parameters. " In the case when results suggest that polymer is compatible with plasticizer in the whole range of concentrations, it is possible to use one of the above given equations. 

Polymer dissolution is a necessary step in many of the polymer processing methods, such as blending, separation, coating, casting, etc. The developments in physical chemistry of non-electrolyte solutions relate the capabilities of solvents to dissolve materials with their physical properties. The relationships were developed within the framework of the concept of solubility parameters. 

The concept of solubility parameters (Hansen, 1967) was first introduced by Charles M. Hansen in 1967 in his PhD thesis where he evaluated whether one material would... 

In the same year Nemst also considered the equilibrium between a sparingly soluble salt and its saturated solution. He introduced the concept of solubility product and used it to explain precipitation processes. 

The concept of solubility parameters as it relates to the internal energy of solutions and solutes was first proposed by Hildebrand in 1916 [1]. Internal pressure is the energy required to vaporize one cubic centimeter of a sub-... 

To understand the concept of solubility, consider the process of dissolving sodium chloride in water. Sodium chloride is an ionic substance and it dissolves in water as Na and Cl ions. If you could view the dissolving of sodium chloride at the level of ions, you would see a dynamic process. Suppose you stir 40.0 g of sodium chloride crystals into 100 mL of water at 20°C. Sodium ions and chloride ions leave the surface of the crystals and enter the solution. The ions move about at random in the solution and may by chance collide with a aystal and stick, thus returning to the aystalline state. As the sodium chloride continues to dissolve, more ions enter the solution, and the rate at which they return to the aystalline state increases (the more ions in solution, the more likely ions are to collide with the crystals and stick). Eventually, a dynamic equilibrium is reached in which the rate at which ions leave the crystals equals the rate at which ions return to the crystals (see Figure 12.2). You write the dynamic equilibrium this way ... 

The transport rates of the reactants generally influence the reaction rates. The transport of a component from one phase into another is determined by two different factors the phase equilibrium and the transport rate coefficients in each of the phases. The phase equilibrium describes the concentration ratio at either side of the interface. For describing these we use the concepts of solubility, volatility Henry coefficient, distribution coefficient, etc.. 

The concept of solubility parameters as it relates to the internal energy of a solution and solute was first introduced by Hildebrand (1916, 1970). Internal pressure is defined as the energy needed to vaporize one cubic centimeter of a substance. In Hildebrand s theory molecules with similar internal pressures will attract and interact with each other. Internal energy is described by the cohesive energy density (CED). The theory predicts that dissolution of a solute will occur in a solvent or solvent blend having similar CED value. Solubility parameters in the originally stated theory have the units of (cal/cm ). In modern SI convention the units are as follows ... 

So is called the intrinsic solubility of M. It is also often called the solubility of MX. It is expressed in mol/L. It must not be confused with the solubility product. Note that in order to apply the notion of solubility, MX may be a dissociable molecule. It can also be an ion pair. When MX is nondissociable, of course, the concept of solubility product can no longer be applied. 

The concept of solubility product, as we ve already mentioned, is legitimate because of... 

The theory of solubility parameters was developed by Scatchard in 1931 and further refined by Hildebrand (5). Originally, the concept of solubility parameters was developed to describe the enthalpy of mixing of simple liquids. Afterwards it has been extended to polymers. 

Hildebrand and others " utilized the concept of solubility parameter, 8, to show why some pairs of materials mix more readily than others. The solubility parameter is related to the internal pressure or cohesive-energy density ... 

---