Influence of pH and complexing

Any substance in solution which reacts with one of the ions created in Reaction 1 will shift the equilibrium to the right side and therefore increase the solubility of the solid. So pH will affect the solubility in a range in which one of the ions has important Bronsted acid or base properties. The solubility of NaCl, for instance, should not be influenced

through pH, but when the anion is the conjugate base of a weak acid solubility will raise at low pH. Metal hydroxides and oxides dissolve in acid solution, and on the other hand such type of solids may be precipitated from a solution consisting of a metal ion as the pH is increased. The solubility range relies on the K_sp value: for an instance, Fe(OH)₃ is precipitated at much lower pH than the more soluble Fe(OH)₂. On high pH the acidity of the hydrated metal ion might come into play and amphoteric substances like Al(OH)₃ will dissolve in alkaline solution to provide [Al(OH)₄]^-. Occasionally the conjugate acid of the anion is volatile, or decomposes to generate a gas. So action of an acid on a sulfide will liberate H₂S and on a carbonate CO₂ from the breakdown of carbonic acid. Every = ligand that complexes with the metal ion will also raise solubility. AgCl dissolves in aqueous ammonia through the formation of [Ag(NH₃)₂]⁺. Addition of Cl^-, which initially reduces the solubility of AgCl by the common ion influence (see above), will at high concentrations raise the solubility by forming [AgCl₂]^-. The solubility of a number of amphoteric oxides and hydroxides at high pH can be interpreted as a identical complexing effect with OH^- acting like the ligand.