Intermolecular forces solubility

Solubility, intermolecular forces, partial pressure of a solute gas, temperature... 

From the standpoint of thermodynamics, the dissolving process is the estabHsh-ment of an equilibrium between the phase of the solute and its saturated aqueous solution. Aqueous solubility is almost exclusively dependent on the intermolecular forces that exist between the solute molecules and the water molecules. The solute-solute, solute-water, and water-water adhesive interactions determine the amount of compound dissolving in water. Additional solute-solute interactions are associated with the lattice energy in the crystalline state. 

There have been many attempts to divide the overall solubility parameter into components corresponding to the several intermolecular forces. For example, a so-called three-dimensional solubility parameter concept is built on the assumption that the ced is an additive function of contributions from dispersion (d), polar (p), and H-bonding (h) forces. It follows that... 

Insoluble in water but soluble in nonpolar solvents such as CCl4 or benzene. Iodine is typical of most molecular substances it is only slightly soluble in water (0.0013 mol/L at 25°C), much more soluble in benzene (0.48 mol/L). A few molecular substances, including ethyl alcohol, are very soluble in water. As you will see later in this section, such substances have intermolecular forces similar to those in water. 

Most nonpolar substances have very small water solubilities. Petroleum, a mixture of hydrocarbons, spreads out in a thin film on the surface of a body of water rather than dissolving. The mole fraction of pentane, CsH12, in a saturated water solution is only 0.0001. These low solubilities are readily understood in terms of the structure of liquid water, which you will recall (Chapter 9) is strongly hydrogen-bonded. Dissimilar intermolecular forces between C5H12 (dispersion) and H2O (H bonds) lead to low solubility. 

Polar molecules attract other polar molecules through dipole-dipole intermolecular forces. Polar solutes tend to have higher solubilities in polar solvents than in nonpolar solvents. Which of the following pairs of compounds would be expected to have the higher solubility in hexafluorobenzene, Cf,I... 

At the opposite extreme, molecular solids contain individual molecules bound together by various combinations of dispersion forces, dipole forces, and hydrogen bonds. Conforming to like dissolves like, molecular solids dissolve readily in solvents with similar types of intermolecular forces. Nonpolar I2, for instance, is soluble in nonpolar liquids such as carbon tetrachloride (CCI4). Many organic compounds are molecular solids that dissolve in organic liquids such as cyclohexane and acetone. 

The best solvent for a molecular solid Is one whose Intermolecular forces match the forces holding the molecules in the crystal. For a solid held together by dispersion forces, good solvents are nonpolar liquids such as carbon tetrachloride (CCI4) and cyclohexane (Cg H12) For polar solids, a polar solvent such as acetone works well. Example provides some practice in recognizing solubility types. 

Solvent selectivity is a measure of the relative capacity of a solvent to enter into specific solute-solvent interactions, characterized as dispersion, induction, orientation and coaplexation interactions, unfortunately, fundamental aiq>roaches have not advanced to the point where an exact model can be put forward to describe the principal intermolecular forces between complex molecules. Chromatograidters, therefore, have come to rely on empirical models to estimate the solvent selectivity of stationary phases. The Rohrschneider/McReynolds system of phase constants [6,15,318,327,328,380,397,401-403], solubility... 

The conformation of a polymer in solution is the consequence of a competition between solute intra- and intermolecular forces, solvent intramolecular forces, and solute-solvent intermolecular forces. Addition of a good solvent to a dry polymer causes polymer swelling and disaggregation as solvent molecules adsorb to sites which had previously been occupied by polymer intra- and intermolecular interaction. As swelling proceeds, individual chains are brought into bulk solution until an equilibrium solubility is attained. 

We have already mentioned that silver chloride is readily soluble in liquid ammonia. Because it is slighdy less polar than water and has lower cohesion energy, intermolecular forces make it possible for organic molecules to create cavities in liquid ammonia. As a result, most organic compounds are more soluble in liquid ammonia than they are in water. Physical data for liquid ammonia are summarized in Table 10.2. 

The increased solubility and amorphous nature of this polymer is ascribed to reduced intermolecular forces between the polymer chains owing to the introduction of fluorine atoms and to looser packing owing to the highly distorted diphenylhexafluoroisopropylidene units in the polymer backbone. 

Organic compounds that have the same functional group often have similar physical properties, such as boiling points, melting points, and solubilities. Physical properties are largely determined by intermolecular forces, the forces of attraction and repulsion between particles. Three types of intermolecular forces are introduced below. You will examine these forces further in Chapter 4. 

The Composition of T, All of the T parameters represent a difference in intermolecular forces (imf). This difference results from a transfer of some substrate from one phase p to another. For partition the change is from (aq) to (nonaq). For solubility it is from CP(s) to jP(sqln), while for chromatographle quan titles it is from p (mobile) to (P(fixed). Thus,... 

Physical properties of polymers, including solubility, are related to the strength of covalent bonds, stiffness of the segments in the polymer backbone, amount of crystallinity or amorphousness, and intermolecular forces between the polymer chains. The strength of the intermolecular forces is directly related to the CED, which is the molar energy of vaporization per unit volume. Since intermolecular attractions of solvent and solute must be overcome when a solute (here the polymer) dissolves, CED values may be used to predict solubility. 

---