Chemistry of Ferric Chloride 

Ferric chloride exists in three forms:

  • FeCl3 (Anhydrous form)
  • FeCl3.6H2O (Hydrous form)
  • Fe2Cl6 (Vapour and dimer form)

Preparation:

  • Preparation of anhydrous FeCl3: When hydrated ferric chloride is heated, anhydrous ferric chloride is obtained.
    $$\ce{FeCl3.6H2O->[\Delta]FeCl3 }$$
  • Preparation of hydrous FeCl3When haematite (Fe2O3)or hydrated ferric hydroxide is treated with dil. HCl, we get ferric chloride solution. The solution so obtained is heated to crystallization point to obtain hydrated ferric chloride.
    $$\ce{Fe2O3 + dil. 6HCl->2FeCl3 + 3H2O}$$
    $$\ce{Fe(OH) + dil. HCl ->3FeCl3 + 3H2O}$$
    $$\ce{FeCl3 (aq)->[\Delta]$\underset{\text{Hydrated ferric chloride}}{\ce{FeCl3.6H2O }}$}$$

Physical properties:

  •  It is a covalent compound.
  •  Anhydrous ferric chloride is black colored, deliquescent crystals but hydrated FeCl3 is yellow colored solid.

Chemical properties:

1. Action with heat: Ferric chloride when heated to 700oC gives monomeric ferric chloride and then into FeCl2 and Cl2.
$$\ce{Fe2Cl6->[\Delta]2FeCl3}$$
$$\ce{2FeCl3->[\Delta]2FeCl3 + Cl2 ^ }$$

2. Action with water: Ferric chloride is highly soluble in water. It forms hydrates which is acidic due to hydrolysis.
$$\ce{FeCl3 + 3H2O->Fe(OH)3 + 3HCl}$$

3.Action with SnCl2: It oxidizes SnCl2 to SnCl4.
$$\ce{2FeCl3 + SnCl4->SnCl4 + 2FeCl2}$$

4. Action with nascent hydrogen and H2S : FeCl3 get reduced when reacted with Nascent H2 and H2S gas.
$$\ce{FeCl3 + [H]->[Zn/HCl]FeCl3 + HCl}$$
$$\ce{FeCl3 + H2S->FeCl2 + HCl + H2O}$$

Uses:

  • It is used as a mordant in dye industry.
  •  It is used as an antiseptic in medicine.
  •  It is used as a catalyst in Fridel Craft reaction.

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