Ferric Chloride (FeCl2 or Fe2Cl6)

Preparation:

Anhydrous FeCl3 is obtained by passing dry Cl2 gas over red hot iron.
2Fe + 3Cl2 → 2FeCl3

Hydrated ferric chloride is obtained by dissolving iron in aquaregia or by dissolving Fe2O3 or Fe (OH)3 in HCl. On crystallization FeCl3 solution gives yellow crystals of FeCl3 6H2O.
2Fe + 9HCl + 3HNO3 → 2FeCl3 + 3NOCl + 6H2O
Fe2O3 + 6HCl → 2FeCl3 + 3H2O
Fe (OH)2 + 6HCl → FeCl3 + 3 H2O

FeCl3 (ag) crystallization → FeCl3.6H2O
Yellow crytals

Properties:

• Anhydrous FeCl3 is black amorphous solid while hydrated FeCl3 is yellow crysaline solid.

• At lower temperature (4000c) the vapor density of ferric chloxde corresponds to the molecular formula Fe2Cl6. Fe2Cl6 is chlorine bridged dimeric structure.

At higher temperature (7000c), Fecl3 decompose forming ferrous chloride.
FeCl3 above 700 → 2FeCl2 + Cl2

• Hydrolysis
  The aqueous solution of FeCl3 is acidic due to hydrolysis to form weak base and strong acid.
  FeCl3 + 3H2O → Fe(OH)3 + 3HCl
  Weak base strong acid

• Reaction with potassium Ferro cyanide:
  Ferric chloride reacts with potassium ferro cyanide forming a prussiara blue colouration of ferric ferro cyanide.
  4FeCl3 + 3 K4 [Fe (CN)6]0 → Fe4 [Fe (CN)6]3 + 12KCl
  Prussian blue ferroc ferro cyanide

• Reaction with ammonium thiocyanate:
  Ferric chloride gives a blood red coloration of Ferric thiocyanate with ammonium thiocyanate.
  FeCl3 + 3 NH4CNS → [Fe (CNS)3] + 3NH4Cl
  Ferric thiocyanate
  Blood red

• Reaction with ammonium hydroxide:
  Ferric chloride gives a reddish brown ppt of ferric hydroxide with Ammonium Hydroxide solution.
  FeCl3 + 3NH4OH → Fe (OH)3 + 3NH4Cl
  Ferric hydroxide
  Reddish brown

Uses:

1. It is used in medicine as astrigents and antiseptic.
2. It is used as mordant in dying.
3. It is used as a catalyst in friedal craft’s reaction.
4. It is used to etch metals like Cu, Ag, during making block.