Interaction of Aqueous Ions: A Correlation between the Hydration and Solubility Properties of Inorganic, Organic, and Polymeric Salts Having Mono- or Polyatomic Ions

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Abstract
It is concluded that the solubility of many salts in water is determined by the interaction of hydrated water molecules on the anion and cation. In other words, the solubility sequences of salts can be explained by using previously developed models for hydrated ions and calculated values of the effective dielectric constant (D±) even though such sequences cannot be explained on the bases of polarization of the ions. Salts were divided into three groups: Group I represents those salte which have no tightly bound water (A regions) on their ions. Group II contains salts which consist of one ion having an A region and a counterion which does not. Group III consists of salts where both anion and cation have an A region. The solubility of salts in groups I and n depends primarily on the value of D± of the B region. If both ions have high or if both have low values of D±, then the stability of the hydrates are similar and the solubility of the salt is relatively low compared to dissimilar D± values. For group in salts the solubility of the salt is determined primarily by the strength of the induced, dipole on the positively hydrated water. A comparison of the maximum solubility of the salt with its theoretical maximum molarity based on values of the hydrated radii substantiates the conclusions. From cationic sequence it is possible to determine whether the value of D− for the anion is greater or less than of water and whether positive or negative hydration exists. From anionic sequence it should be possible to determine what cationic groups on protein molecules bind counterions and what cations have positive hydration (A regions). Some polyatomic ions can form chelation structures with the counterion. Such complexes reduce the solubility of the salt if a two-or three-dimensional network can be formed or increase the solubility if such a network cannot be formed.