For which salt in each of the following groups will the solubility depend on pH? a. \(\mathrm{AgF}, \mathrm{AgCl}, \mathrm{AgBr}\) b. \(\mathrm{Pb}(\mathrm{OH})_{2}, \mathrm{PbCl}_{2}\) c. \(\operatorname{Sr}\left(\mathrm{NO}_{3}\right)_{2}, \operatorname{Sr}\left(\mathrm{NO}_{2}\right)_{2}\) d. \(\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2}, \mathrm{Ni}(\mathrm{CN})_{2}\)

Understanding why some salts are more soluble at certain pH levels requires a basic knowledge of acid-base chemistry. Salts are composed of cations and anions, which can interact with H⁺ or OH^- ions in solution, altering their solubility.

For instance, salts that contain the conjugate base of a weak acid will become more soluble in acidic solutions. This is because the excess H⁺ ions in an acidic solution will react with the conjugate base, forming the weak acid, and thereby shifting the equilibrium to dissolve more salt. Conversely, salts containing weak bases will increase in solubility in basic conditions due to the consumption of OH^- by the weak base.

Thus, the pH-dependence of solubility is significant for understanding many biological and environmental processes, as well as for practical applications in pharmaceuticals and chemical synthesis. Salts composed of species derived from strong acids and bases typically show little pH-dependence because their conjugate partners are non-reactive with H⁺ or OH^- ions.

The role of conjugate bases in the solubility of salts is a topic of great significance in chemistry. When an acid donates a proton (H⁺), it forms its conjugate base. The strength of an acid is inversely related to the strength of its conjugate base. That means strong acids have weak conjugate bases, and weak acids have relatively strong conjugate bases.

When a salt contains the conjugate base of a weak acid, such as CN^- from HCN, it has the potential to react with H⁺ ions in solution. This reduces the concentration of the conjugate base and shifts the equilibrium towards the dissolution of more salt to replenish the conjugate base, thereby increasing the solubility of the salt in solution.

Contrastingly, salts derived from strong acids, like Cl^- from HCl, have conjugate bases that are virtually non-reactive with H⁺, making their solubility largely unaffected by pH changes. Recognizing the nature of the conjugate bases in salts is crucial when predicting or explaining their pH-dependent solubility behavior.

Solubility, the tendency of a substance to dissolve in a solvent, is governed by a complex interplay of factors, including temperature, pressure, polarity, and especially, in the case of ionic compounds, the composition of the solvent such as its pH.

The basic principle dictating solubility is 'like dissolves like', where polar substances tend to dissolve in polar solvents, while non-polar substances dissolve in non-polar solvents. Solubility can be quantitatively expressed by the solubility product constant (K_sp), which defines the equilibrium between dissolved ions and the undissolved solid in a saturated solution.

For salts, solubility can vary widely. Some are highly soluble in water, like sodium chloride (NaCl), while others have very low solubility, such as silver chloride (AgCl). The pH of the solution can alter the solubility of salts that can react with H⁺ or OH^-. By manipulating the pH, one can often precipitate or dissolve salts selectively, a technique widely used in chemical analysis and separation methods such as selective precipitation and extraction.