Phosphorus Pentachloride (PCl5) | Preparation, Structure, Physical and Chemical Properties
Preparation: Phosphorus pentachloride is usually prepared by the action of an excess of chlorine on phosphorus trichloride.
PCl3 + Cl2 gives PCl5
Physical properties
1. Phosphorus pentachloride is a yellowish white crystalline solid.
2. It sublimes on heating at 473 Kelvin and melts at 318 Kelvin under pressure.
Chemical properties
1. Phosphorus pentachloride dissociates on heating into phosphorus trichloride and chlorine.
PCl5 on dissociating gives PCl3 + Cl2
2. It is violently hydrolysed by water giving phosphorus oxychloride or phosphoric acid depending upon the quantity of water.
Phosphorus pentachloride plus insufficient water gives Phosphorus oxychloride plus Hydrochloric Acid.
Phosphorus pentachloride plus excess of water gives ortho phosphoric Acid plus Hydrochloric Acid.
3. It reacts with compounds containing hydroxyl groups forming chloro derivatives. In all these cases, the hydroxyl group is replaced by chlorine.
Ethyl Alcohol plus Phosphorus pentachloride gives Ethyl Chloride plus Phosphorus oxychloride plus Hydrochloric Acid.
4. It reacts with metals on heating to give corresponding chlorides.
Silver plus Phosphorus pentachloride gives silver chloride plus Phosphurus trichloride.
Structure
Phosphorus pentachloride molecule has a trigonal bipyramidal shape in vapour state which arises from sp3d hybridisation of phosphorus atom.