Laboratory Preparation of Phosphorus Pentachloride - QS Study
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Preparation: Phosphorus pentachloride (PCl5) is usually prepared by the action of an excess of chlorine on phosphorus trichloride.

PCl3 + Cl2 → PCl5

 

Physical properties

  • Phosphorus pentachloride is a yellowish white crystalline solid.
  • It sublimes on heating at 473 K and melts at 318 K under pressure.

 

Chemical properties

a. Phosphorus pentachloride dissociates on heating into phosphorus trichloride and chlorine.

PCl5 ↔ PCl3 + Cl2

b. It is violently hydrolysed by water giving phosphorus oxychloride or phosphoric acid depending upon the quantity of water.

  • PCl5 + H2O (insufficient of water) → POCl3 + 2HCl
  • PCl5 + 4H2O (Excess of water) → H3PO4 + 5HCl

c. It reacts with compounds containing hydroxyl groups forming chloro derivatives. In all these cases, the hydroxyl group is replaced by chlorine.

C2H5OH (Ethyl Alcohol) + PCl5 → C2H5Cl (Ethyl Chloride) + POCl3 + HCl

d. It reacts with metals on heating to give corresponding chlorides.

2Ag + PCl5→2 AgCl + PCl3

 

Structure

PCl5 molecule has trigonal bipyramidal shape in vapour state which arises from sp3d hybridization of phosphorus atom.

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