Green and Blue Copper Complexes

Purpose:

To demonstrate that different ligands exhibit different colors in a coordination complex.

Materials:

• Pipette
• Large graduated cylinder

Reagents:

• Concentrated ammonia (NH₃)
• Concentrated hydrochloric acid (HCl)
• 0.2M Copper sulfate (CuSO₄⋅H₂O_(s))

Hazards and PPE:

• Copper sulfate is a skin irritant and harmful if ingested. Handle with care.
• Hydrochloric acid is acutely corrosive and toxic. Avoid skin contact and inhalation of fumes.
• Concentrated ammonia can cause severe skin burns and respiratory irritation, and is an extreme aquatic toxin. Store and handle with care.
• Wear approved safety goggles and gloves.

Protocol:

Demonstration

1. Fill the graduated cylinder ~1/4 with CuSO₄ solution.
2. Add HCl until a pale green solution is formed.
3. Use pipette to add NH₃ until a deep blue color forms. The deep blue solution should sit above the green solution.

Disposal:

• Solutions should be placed in properly labeled waste containers.

Reactions:

• Cu(H₂O)₄²⁺_(aq) + 4Cl^- ⇌ CuCl₄^2-_(aq) + 4H₂O_(l)
• CuCl₄^2-_(aq) + 4NH₃ ⇌ Cu(NH₃)₄²⁺_(aq) + 4Cl^-_(aq)
• The tetraaquacopper (II) and tetraaminecopper (II) complexes have a square planar structure. The tetrachlorocopper (II) complex has a tetrahedron structure.

Citations:

1. Summerlin, L., Borgford, C., & Ealy j. Chemical Demonstrations: A Sourcebook for Teachers, Volume 2, Second Edition, 1988.

Videos:

• Simple Complex Ion Demo with Cu

  MrGrodskiChemistry

  This video features a different procedure than I describe, but the principles illustrated are the same.