What is the insoluble nature of compounds

The process of dissolution between solute and solution involves intermolecular forces. When it comes to the properties of solutes and solutions, solutions are generally divided into two types, polar and non-polar. What we know as the "similar compatibility principle" is essentially about the forces between molecules.

When a non-polar gas is dissolved in a solvent, it mainly depends on the dispersion between solute and solvent molecules. Even in polar solvents, the contribution of induction is very small. Thus, as the polarizability of the gas molecules increases, the solubility increases accordingly. The influence of solvent properties is more complex. When the solvent polarizability increases, although it is conducive to the interaction between solute and solvent, the interaction between solvent molecules is also enhanced, which is not conducive to dissolution.

In general, the solubility of polar substances in non-polar solvents is relatively small, while the solubility of polar solvents is larger. On the contrary, non-polar substances are more easily dissolved in non-polar solvents, and the solubility in polar solvents is smaller. The solution formed by polar and non-polar substances is usually positively deviated, and the vapor pressure is higher than the ideal solution value, and the boiling point is lower.

The formation of hydrogen bond has significant effect on the properties of the mixture. For example, chloroform and acetylene dissolve well in ether and acetone, because they essentially form a complex. For some substances, however, it depends on differences in the formation of complexes and their self-association strength. For example, chloroform can be dissolved in methanol well because the effect of chloroform and methanol is stronger than the self-association of methanol.

But chloroform is hard to dissolve in water because water is so self-associative. But dioxane (1, 4-dioxane) dissolves in water, suggesting that it is strong enough to compete with water as a proton acceptor. The formation or destruction of hydrogen bond will cause the vapor pressure and boiling point of solution to deviate from the ideal.

For example, ethanol self-association is very strong, when dissolved in carbon tetrachloride, due to dilution, the degree of association is reduced, so the vapor pressure is increased, and the formation of a low constant boiling point. Acetone and chloroform form complex, the vapor pressure is reduced, forming a high constant boiling point.

But things get a little more complicated when you mix things, like dioxane and acetic acid, and on the one hand they form an intermolecular hydrogen bond that lowers the vapor pressure, and on the other hand the dissociation of the self-associated acetic acid raises the vapor pressure, and in this case, the vapor pressure still drops as a result of competition between the two, creating a high constant boiling point. Of course, hydrogen bonding is only one of the reasons, and the influence of other types of intermolecular forces should also be considered.