Changing the pH of a solution can affect the equilibrium constant Kf for the formation of Fe CN 6 4- complex ion in a solution containing Fe3+ and CN- ions. To understand this, let's first look at the chemical reaction for the formation of the complex ion:Fe3+ + 6CN- <=> Fe CN 6 4-The equilibrium constant Kf for this reaction is given by:Kf = [Fe CN 6 4-] / [Fe3+][CN-]^6 Now, let's consider the effect of pH on this reaction. The pH of a solution is a measure of the concentration of H+ ions, which can affect the concentrations of the reactants and products in the reaction.1. Effect of pH on Fe3+ ions:Fe3+ ions can hydrolyze in water to form Fe OH 3 and H+ ions:Fe3+ + 3H2O <=> Fe OH 3 + 3H+When the pH of the solution is increased more basic , the concentration of H+ ions decreases, which shifts the equilibrium of this reaction to the right, forming more Fe OH 3 and decreasing the concentration of Fe3+ ions. This, in turn, affects the equilibrium of the complex ion formation reaction.2. Effect of pH on CN- ions:CN- ions can react with H+ ions to form HCN:CN- + H+ <=> HCNWhen the pH of the solution is increased more basic , the concentration of H+ ions decreases, which shifts the equilibrium of this reaction to the left, increasing the concentration of CN- ions.Now, let's combine these effects on the equilibrium constant Kf for the formation of the Fe CN 6 4- complex ion. When the pH is increased, the concentration of Fe3+ ions decreases, and the concentration of CN- ions increases. According to the expression for Kf, this will result in an increase in the concentration of Fe CN 6 4- complex ion, and thus an increase in the value of Kf.In summary, changing the pH of a solution can affect the equilibrium constant Kf for the formation of Fe CN 6 4- complex ion in a solution containing Fe3+ and CN- ions. Increasing the pH making the solution more basic will generally result in an increase in the value of Kf, due to the decrease in Fe3+ ion concentration and the increase in CN- ion concentration.