The position of the chemical equilibrium of a reaction can be influenced in accordance with Le Chatelier's principle. For example, one possibility is to alter the change in concentration of the reactants involved. In this experiment, students make a hexaaqua copper complex, convert it to a dichlorocopper complex by adding chloride ions, and then shift the equilibrium between the two complexes by adding water again and adding chloride ions again. Using the different colourations of the two copper complexes, students can easily observe the shift in equilibrium.