A change in pH can affect the formation of the complex ion Fe III -thiocyanate by altering the concentrations of the reactants and the stability of the complex. The formation of the Fe III -thiocyanate complex can be represented by the following equation:Fe + SCN FeSCNIn acidic conditions low pH , the concentration of H ions is high. This can lead to the protonation of the thiocyanate ion SCN to form HSCN:H + SCN HSCNAs a result, the concentration of free SCN ions decreases, which can shift the equilibrium of the Fe III -thiocyanate complex formation to the left, reducing the formation of the complex.On the other hand, in basic conditions high pH , the concentration of OH ions is high. This can lead to the formation of Fe OH precipitate:Fe + 3OH Fe OH s This reaction removes Fe ions from the solution, which can also shift the equilibrium of the Fe III -thiocyanate complex formation to the left, reducing the formation of the complex.Now, to determine the equilibrium constant K for this reaction at a pH of 2.5, we need to know the concentrations of the reactants and products at equilibrium. Unfortunately, without this information, it is not possible to calculate the exact value of K. However, it is important to note that the optimal pH range for the formation of the Fe III -thiocyanate complex is typically between 1 and 2. Since the pH of 2.5 is close to this range, the equilibrium constant should still be reasonably high, indicating a significant formation of the complex.