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). Copper dusts and mists carry an occupational exposure limit expressed 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. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.