Increasing the pH of a solution containing iron III and cyanide ions will favor the formation of the iron III -cyanide complex ion. This is because cyanide ions CN- act as a ligand and can form coordination complexes with metal ions, such as iron III ions Fe3+ . The formation of the iron III -cyanide complex ion can be represented by the following equilibrium reaction:Fe3+ + 6CN- <=> Fe CN 6^3-As the pH of the solution increases, the concentration of hydrogen ions H+ decreases. Cyanide ions can react with hydrogen ions to form hydrogen cyanide HCN , as shown in the following reaction:CN- + H+ <=> HCNWhen the pH increases, this reaction is shifted to the left, resulting in a higher concentration of cyanide ions CN- in the solution. The increased concentration of cyanide ions will then shift the equilibrium of the iron III -cyanide complex formation to the right, favoring the formation of the complex ion Fe CN 6^3-.