A solution of copper(II) chloride demonstrates equilibrium between aqua and chloride complexes of copper(II). By changing temperature, solvent, or ion concentration, the equilibrium shifts and visible color changes occur.

1. Prepare a test tube half filled with 1.5 M copper(II) chloride solution.
2. Use a dropper to divide the solution evenly into five test tubes.
3. To Tube 2, add solid calcium chloride in small amounts, dissolving each portion until no more dissolves, and note the color change.
4. To Tube 3, add enough ethyl alcohol to triple the solution’s volume, mix, and observe the color.
5. Place Tube 4 in a hot-water bath, heat until warm, and observe the color change.
6. Place Tube 5 in an ice-water bath, cool thoroughly, and observe the color change.

Colorful Copper Equilibrium - Tommy Technetium:

Effect of Temperature on Chemical Equilibrium using Copper Complexes - Chem Ed Xchange:

📄 Complex Ions of Copper(II) (Cu2+) (Page 4) - Science Learning Centre: https://www.chemedx.org/blog/effect-temperature-chemical-equilibrium-using-copper-complexes

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• Wear safety goggles and lab coat.
• Handle copper(II) chloride with care; it is toxic and harmful if ingested.
• Avoid skin contact with copper solutions and calcium chloride.
• Ethyl alcohol is flammable; keep away from flames or sparks.
• Use caution with hot water baths to avoid burns.
• Do not pour solutions down the drain.

• What are the colors of the different copper complexes? (CuCl4^2– is green, Cu(H2O)4^2+ is light blue.)
• How does adding chloride ions shift the equilibrium? (It favors CuCl4^2– formation, giving a green color.)
• Why does cooling the solution affect the position of equilibrium? (The equilibrium is temperature dependent; cooling favors one complex, heating favors the other.)
• How does adding ethyl alcohol affect the equilibrium? (It reduces the effective dielectric constant of the solvent, changing ion stabilization and shifting equilibrium.)