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. Soluble iron salts carry a low airborne limit as Fe, so keep mist and dust down. 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. 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.