Iron(III) Chloride Hexahydrate
Properties
| State | Solid (crystalline, deliquescent) |
| Color | Yellow-brown to orange |
| Solubility | Very soluble in water (920 g/L at 20°C); soluble in ethanol and acetone |
| Melting Point | 37°C |
| Boiling Point | 280-285°C (decomposes) |
About Iron(III) Chloride Hexahydrate
Iron(III) chloride hexahydrate is the orange-yellow, deliquescent form of FeCl3 you actually get when you order ferric chloride from any chemical supplier — the anhydrous form is a pain to handle because it absorbs water from the air within seconds. Dissolved in water, FeCl3·6H2O gives a dark brown solution that's strongly acidic (pH around 1-2 for a 1 M solution) thanks to extensive hydrolysis of the [Fe(H2O)6]3+ cation. The hexahydrate is the etchant of choice for hobbyist and small-shop printed circuit board fabrication: a 40-45% w/w solution will dissolve copper at roughly 1-2 µm per minute at 50°C via 2FeCl3 + Cu → CuCl2 + 2FeCl2. It's also the standard primary coagulant in municipal wastewater treatment — Fe(III) hydrolyzes to a gelatinous Fe(OH)3 floc that captures suspended solids, phosphate (as FePO4), and dissolved metals. The catch with the hexahydrate: those six bound water molecules block the iron coordination sites, so it's useless as a Friedel-Crafts catalyst. For Lewis-acid chemistry you need anhydrous FeCl3.
Where you'll encounter it
If you've ever etched a PCB at home, treated swimming pool water, or watched a styptic pencil stop a shaving cut from bleeding, you've used FeCl3·6H2O. The hobbyist electronics scene runs on this stuff — drop a copper-clad board into a heated 40% solution and the orange liquid bubbles around the artwork mask, leaving sharp circuit traces in 10-15 minutes. Down at the municipal water plant a few blocks over, the same compound goes in by the truckload at 5-50 mg/L to coagulate the silt and bacteria out of raw river water before it reaches your tap. Dental hygienists keep small bottles of dilute FeCl3 solution to stop bleeding after deep cleanings — the Fe(III) ions denature blood proteins on contact, sealing capillaries faster than gauze pressure alone.
Common Uses
- Copper etchant for hobbyist and small-shop PCB fabrication at 40-45% w/w
- Primary coagulant in municipal wastewater treatment plants
- Phosphate removal in tertiary sewage treatment via FePO4 precipitation
- Hemostatic styptic in dental practice and consumer styptic pencils
- Drinking-water clarification at typical doses of 10-50 mg/L
- Industrial sludge dewatering aid
- Sour gas scrubbing in petroleum processing
Safety Information
Strongly corrosive in solution, with skin-contact pH around 1. GHS classifications: H290 (corrosive to metals), H302 (harmful if swallowed), H314 (causes severe skin burns and eye damage). Solutions stain skin a persistent dark yellow-brown for several days because Fe(III) binds keratin, and they will stain stainless steel, grout, and clothing permanently. OSHA PEL for soluble iron salts is 1 mg/m3 as Fe. Use nitrile gloves (latex degrades quickly), splash goggles, and a chemical apron. Spills neutralize with soda ash before water rinsing.
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.