Copper(II) Chloride
Properties
| State | Solid at room temperature |
| Color | Yellow-brown (anhydrous), blue-green (dihydrate) |
| Solubility | Very soluble in water (75.7 g/100 mL at 25°C) |
| Melting Point | 498°C (anhydrous) |
| Boiling Point | 993°C (decomposes) |
About Copper(II) Chloride
CuCl₂ is one of the cleanest demonstrations of crystal-field theory you can put on a benchtop. The anhydrous salt is a yellow-brown polymeric chain solid (CuCl₂ chains with bridging chlorides), the dihydrate CuCl₂·2H₂O is blue-green and forms the mineral eriochalcite, and a concentrated aqueous solution shifts from blue to green to yellow as you add chloride and the coordination sphere shifts from [Cu(H₂O)₆]²⁺ (octahedral, blue) to [CuCl₄]²⁻ (distorted tetrahedral, yellow). Diluting with water reverses the color back to blue — a textbook example of Le Chatelier and ligand-field strength happening over a few seconds. The Jahn-Teller distortion of d⁹ Cu(II) shows up everywhere: the four equatorial Cu–Cl distances are short and the two axial positions are elongated, which is why CuCl₂ rarely forms a true regular octahedron. In industry the biggest use is PCB etching: an acidified CuCl₂/HCl bath dissolves exposed copper through Cu + CuCl₂ → 2CuCl, then bubbled air or HCl + O₂ regenerates Cu(II) from Cu(I), so the same etchant runs continuously rather than being thrown out like ferric chloride baths. CuCl₂ also catalyzes oxychlorination of ethylene to 1,2-dichloroethane in vinyl chloride manufacture — millions of tonnes a year of PVC monomer flow through a CuCl₂/Al₂O₃ catalyst bed. In organic synthesis, CuCl₂ is a mild oxidant for converting α-methylene ketones to α-chloro ketones and for radical cyclization initiation.
Where you'll encounter it
If you've ever made a flame-test demonstration burn green-blue, you probably soaked a wooden splint in CuCl₂ solution — the green flame comes from CuCl* emission around 526 nm in the cool outer cone. If you've seen a printed circuit board being made, the etch tank is full of acidic CuCl₂ that turns from yellow-green to dark brown as it loads with dissolved copper, then gets regenerated by bubbling chlorine or HCl + air. The blue-to-green Le Chatelier color shift is one of the most-photographed undergraduate equilibrium demonstrations.
Common Uses
- Etchant for printed circuit boards via Cu + CuCl₂ → 2CuCl, regenerated continuously with HCl/O₂
- Oxychlorination catalyst for ethylene → 1,2-dichloroethane in PVC monomer manufacture
- Mild oxidant for α-chlorination of ketones and radical chain initiation in synthesis
- Lewis acid promoter in Diels–Alder and aldol-type reactions under mild conditions
- Mordant for fixing dyes onto cotton and wool in textile finishing baths
- Green-blue colorant for flame-test demonstrations and pyrotechnic compositions
- Source of Cu(II) for electroplating bath formulations and copper recovery streams
- Wood preservative component in copper-based timber treatments before chromated alternatives
Safety Information
GHS: H302 (harmful if swallowed), H315 (skin irritation), H319 (eye irritation), H410 (very toxic to aquatic life). OSHA PEL for copper dusts/mists 1 mg/m³ as Cu. Acidic CuCl₂ etch baths additionally evolve HCl vapor — local exhaust ventilation required, and contact with skin gives the characteristic copper-chloride green stain that needs prompt washing because of low-grade burns from both the acidity and the Cu²⁺ itself. Concentrated solution will pit stainless steel through pitting corrosion accelerated by chloride; use HDPE or glass containers.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.