A solution of copper ions undergoes visible color changes when ligands such as chloride or ammonia are added. This demonstrates Le Châtelier’s Principle, as the equilibrium shifts to counteract changes in concentration of ligands.

1. Prepare a blue solution of copper(II) chloride in water.
2. Add sodium chloride or hydrochloric acid to increase chloride ion concentration. Observe the color change toward green or yellow as chloro-complexes form.
3. Add aqueous ammonia to the solution. Observe the shift to a deep blue color as ammine complexes form.
4. Dilute with water to reverse the reaction back toward hydrated copper complexes.
5. Optionally, adjust temperature (warming or cooling) to observe further equilibrium shifts.

LeChatelier's Principle Demo - Copper Complexes - Mr. Z Physical Science:

Le Chatelier's Principle: Part A - Copper(II) and Ammonia Equilibrium - Morgan Stock:

• Add different amounts of chloride or ammonia to observe intermediate equilibrium positions.
• Compare the effect of temperature changes on equilibrium.

• Safety goggles and gloves required.
• Handle ammonia solution in a well-ventilated area.
• Take care when handling hydrochloric acid or other strong acids.
• Dispose of copper-containing solutions with the appropriate waste.

• What color changes occur when chloride is added? (Shift toward yellow-green chloro complexes.)
• What happens when ammonia is added? (Formation of deep blue ammine complexes.)
• Why does dilution with water shift the equilibrium? (It reduces ion concentration, favoring hydrated copper complexes.)
• How does this experiment illustrate Le Châtelier’s Principle? (The equilibrium shifts to counteract the change in concentration of ligands.)
• What effect might temperature have on this equilibrium? (It may favor one complex over another depending on whether the forward reaction is endothermic or exothermic.)