A change in pH can significantly affect the formation of complex ions in a chemical equilibrium system. Complex ions are formed when a central metal ion is surrounded by ligands, which are molecules or ions that can donate a pair of electrons to the metal ion. The formation of complex ions can be influenced by the acidity or alkalinity of the solution, as the pH affects the concentration of H+ and OH- ions in the system.When the pH of a solution changes, it can alter the equilibrium between the complex ions and their constituent species. This can lead to either the formation or dissociation of complex ions, depending on the specific reaction and the direction of the pH change.There are two main ways in which pH changes can affect complex ion formation:1. Protonation or deprotonation of ligands: Some ligands can either gain or lose a proton H+ depending on the pH of the solution. When the pH changes, the ligands may become protonated or deprotonated, which can affect their ability to form complex ions with metal ions. For example, consider the formation of a complex ion between a metal ion M and a ligand L that can be protonated:M + L <-> MLIf the pH decreases i.e., the solution becomes more acidic , the concentration of H+ ions increases, and the ligand L may become protonated to form LH+. This protonated ligand is less likely to form a complex ion with the metal ion, causing the equilibrium to shift to the left and decreasing the concentration of the complex ion ML .2. Competition between H+ or OH- ions and ligands: In some cases, H+ or OH- ions can compete with ligands for binding to the metal ion. When the pH changes, the concentration of H+ or OH- ions in the solution may increase or decrease, affecting the formation of complex ions. For example, consider the following equilibrium involving a metal ion M , a ligand L , and H+ ions:M + L + H+ <-> MLH+If the pH decreases i.e., the solution becomes more acidic , the concentration of H+ ions increases, causing the equilibrium to shift to the right and promoting the formation of the MLH+ complex ion. Conversely, if the pH increases i.e., the solution becomes more alkaline , the concentration of H+ ions decreases, causing the equilibrium to shift to the left and promoting the dissociation of the MLH+ complex ion.Examples:1. The formation of the hexaaquacopper II ion, [Cu H2O 6]2+, can be affected by pH changes. When the pH decreases, the H+ ions can compete with water molecules for binding to the copper ion, leading to the formation of the hydroxocopper II ion, [Cu H2O 5OH]+. This causes the equilibrium to shift and the concentration of the hexaaquacopper II ion to decrease.2. The complexation of iron III ions with EDTA ethylenediaminetetraacetic acid is affected by pH changes. At low pH, the EDTA ligand is protonated and less able to form a complex ion with the iron III ion. As the pH increases, the EDTA ligand becomes deprotonated and more able to form a complex ion with the iron III ion, leading to an increase in the concentration of the Fe EDTA complex ion.In summary, changes in pH can significantly affect the formation of complex ions in a chemical equilibrium system by altering the protonation state of ligands and the competition between H+ or OH- ions and ligands for binding to metal ions. This can lead to either the formation or dissociation of complex ions, depending on the specific reaction and the direction of the pH change.