The formation of a complex ion between Fe3+ and SCN- can be represented by the following equilibrium reaction:Fe3+ aq + SCN- aq FeSCN2+ aq The equilibrium constant for this reaction is given by:K = [FeSCN2+] / [Fe3+][SCN-] When the pH of the solution is increased, the concentration of H+ ions decreases. This can affect the formation of the complex ion in several ways.1. Formation of hydroxide complexes: As the pH increases, the concentration of OH- ions increases. This can lead to the formation of hydroxide complexes with Fe3+ ions, such as Fe OH 2+ and Fe OH 2+. The relevant reactions are:Fe3+ aq + OH- aq Fe OH 2+ aq Fe3+ aq + 2OH- aq Fe OH 2 aq These reactions will decrease the concentration of free Fe3+ ions in the solution, shifting the equilibrium of the FeSCN2+ complex formation to the left, and thus reducing the formation of the complex ion.2. Deprotonation of SCN-: As the pH increases, SCN- can undergo deprotonation to form HSCN:SCN- aq + H2O l HSCN aq + OH- aq This reaction will decrease the concentration of free SCN- ions in the solution, also shifting the equilibrium of the FeSCN2+ complex formation to the left, and reducing the formation of the complex ion.3. Formation of other complexes: At higher pH values, other metal ions present in the solution may form complexes with SCN-, further reducing the concentration of free SCN- ions and decreasing the formation of the FeSCN2+ complex.In summary, increasing the pH of the solution can lead to a decrease in the formation of the FeSCN2+ complex ion due to the formation of hydroxide complexes with Fe3+, deprotonation of SCN-, and the formation of other complexes with SCN-. This can be observed as a decrease in the intensity of the red color associated with the FeSCN2+ complex.