Changing the pH of a solution containing both Fe and CN ions will affect the formation of the complex ion Fe CN . The formation of this complex ion is governed by the following equilibrium reaction:Fe aq + 6CN aq Fe CN aq The equilibrium constant for this reaction, Kf, is given by:Kf = [Fe CN ] / [Fe][CN] Now, let's consider the effect of pH on this equilibrium. The CN ion is the conjugate base of the weak acid HCN:HCN aq + HO l HO aq + CN aq The equilibrium constant for this reaction, Ka, is given by:Ka = [HO][CN] / [HCN]As the pH of the solution changes, the concentration of HO ions changes as well. When the pH decreases more acidic conditions , the concentration of HO ions increases. This will shift the HCN equilibrium to the left, decreasing the concentration of CN ions in the solution. With a lower concentration of CN ions, the complex ion formation equilibrium will also shift to the left, resulting in a lower concentration of Fe CN complex ions.Conversely, when the pH increases more basic conditions , the concentration of HO ions decreases. This will shift the HCN equilibrium to the right, increasing the concentration of CN ions in the solution. With a higher concentration of CN ions, the complex ion formation equilibrium will shift to the right, resulting in a higher concentration of Fe CN complex ions.In summary, decreasing the pH more acidic conditions will decrease the formation of the Fe CN complex ion, while increasing the pH more basic conditions will increase the formation of the Fe CN complex ion. This can be explained by the effect of pH on the concentration of CN ions, which in turn affects the position of the complex ion formation equilibrium.