Cobalt chloride equilibrium. The flask on the left contains a cobalt (II) chloride solution that has a low concentration of chloride ions. The cobalt in the solution is complexed with water molecules and retains its natural aqueous pink colour. The flask on the right contains cobalt (II) chloride solution, that has a high concentration of chloride ions. The cobalt in the solution is complexed with chloride ions and so the solution changes colour to blue. This equilibrium is sensitive to temperature as well as concentration of solutes.