Solubility making predictions

Because solubility and viscosity are non-equilibrium properties, the measured values are dependent upon measurement conditions, sample preparation, and past sample history. Because of this, it is difficult or sometimes even impossible to compare data, to generalize the data and make predictions, and to interpret the data in terms of the basic molecular forces. 

Many interrelated factors affect the solubility of substances in water. This makes it challenging to predict which ionic substances will dissolve in water. By performing experiments, chemists have developed guidelines to help them make predictions about solubility. In Investigation 9-A, you will perform your own experiments to develop quidelines about the solubility of ionic compounds in water. 

He then proceeded to break 15) the solvent bulk parameter into respective dispersion forces Keesom, or polarity forces hydrogen bonding forces and London forces. He did the same for the polymers which were under his consideration. He con ared these parameters for solvents and polymers term-wise, and analyzed their differentials in order to make predictions concerning their solubility interactions. In conducting 10,000 interaction experiments involving solvents and polymers, he found that he could make accurate predictions in 971 of the cases using his C.E.D. refinements. 

The steroids as a group tend to be poorly soluble in water. Their complex stmcture makes prediction of solubility somewhat difficult, but one can generally rationalise, post hoc, the solubility values of related steroids. Table 5.6 gives solubility data for 14 steroids. As examples, the substitution of an ethinyl group has conferred increased solubility on the estradiol molecule, as would be expected. Estradiol benzoate with its 3-OH substituent is much less soluble than the parent estradiol because of the loss of the hydroxyl and its substitution with a hydrophobic group. The same relationships are seen in testosterone and testosterone propionate. As both estradiol benzoate and testosterone propionate are oil soluble, they are used as solutions in castor oil and sesame oil for intramuscular and subcutaneous injection (see Chapter 9). 

The factors that determine whether or not an ionic compound will be soluble in water are complex, making predictions difficult. As a result, a series of statements or rules have come into being that guide predictions. These rules are called the solubility rules. As with most general rules, exceptions exist, but they are correct most of the time. The following rules are organized in a hierarchal structure—that is, the first rule takes precedence over the second, the second over the third, and so forth. 

How do you know whether a precipitate will form Readily available solubility tables, such as Table 7.1, make prediction rather easy. 

It is, therefore, seen that only when Fab—Faa and Fab—Fbb will coexistence or compatibility be possible. Obviously, if it is possible to obtain some measure of these forces, it should be possible to make predictions about polymer solubility. What then is a suitable measure of the forces holding like molecules together One would expect the latent heat of vaporization, L, to exceed the cohesion energy by an amount corresponding to the work done by evaporation, an amount approximating to RT, where R is the gas constant and T the absolute temperatore. Such a diagram of (L—RT) might be a sufficient measure if all of the molecules were of about the same size. 

Extensive use of the three-dimensional solubility parameters for predicting adhesion seems not to have been made, although its additional flexibility should make it successful over a wider range of conditions than the single-parameter approach. Some recent studies involving dental adhesion employed the method with success. Asmussen and Uno fl40 successfully correlated the shear bond strength of various dental adhesive resins, characterized in terms of their three-... 

Here is a rule of thumb that can help us predict solubility in order to have a high water-solubility, there should be no more than 5 carbon atoms per OH group. A compound with two OH groups and 7 carbon atoms will be very soluble in water. A compound with one OH group and 7 carbon atoms will NOT be very soluble in water. There are, of course, many exceptions to this simplified rule of thumb, but the rule can be helpful whenever we need to make a quick prediction about the solubility of an alcohol. 

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