Curriculum Notes 

This demo can be used to demonstrate Le Chatelier's principle. It can also be used when complex ion formation and equilibria are being discussed. Allow about 10 minutes for this demo.

One day of lead time is required for this project.

Discussion 

The simplest way of representing this system is:

$\ce{CuCl4^{2-}_(green) + 6 H2O <=> Cu(H2O)6^{2+}_(blue) + 4 Cl^{-} }$

This equilibrium is probably the best one to present for a discussion of Le Chatelier's principle in an intro Gen Chem class, but the system is probably more complicated, possibly involving the formation of mixed complexes. The addition of water pushes the equilibrium to the right, and the addition of concentrated hydrochloric acid shifts the equilibrium to the left. 

Materials 

• 500 mL three-necked round-bottom flask containing 200 mL of 0.1M copper(II) chloride dihydrate in 95% ethanol and a magnetic stir bar, 24/40 vertical ground glass joints.
• vented addition funnel w/stopper containing 150 ml of concentrated hydrochloric acid, 24/40 ground glass joints.
• addition funnel containing 150 ml of distilled water, 24/40 ground glass joints.
• ring stand and clamps to secure apparatus.
• magnetic stir plate.
• white background (optional)

Procedure 

• turn on stir plate
• add water until the solution turns pale blue
• add concentrated hydrochloric acid until the solution turns back green
• continue to alternate water and acid until the flask becomes close to full

Safety Precautions 

• Concentrated hydrochloric acid and the vapors that it emits are extremely caustic and corrosive. Avoid breathing the vapors. If concentrated hydrochloric acid comes into contact with your skin, flush with copious amounts of water. If you get some in you eyes, flush with water for at least 15 minutes and seek medical attention. Wear goggles.
• Copper(II) chloride is poisonous. In case of ingestion, induce vomiting immediately as directed by medical personnel. Never give anything by mouth to an unconscious person. Call a physician immediately. In case of skin contact, wipe off excess material from skin then immediately flush skin with plenty of water for at least 15 minutes. Remove contaminated clothing and shoes. Wash clothing before reuse. Call a physician. In case of eye contact, immediately flush eyes with plenty of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Get medical attention immediately