Give the preparation of phosphorus trichloride and phosphorus pentachloride.

Explanation

Preparation of phosphorus trichloride (`PCl_3`) : It is obtained by passing dry chlorine over heated white phosphorus
`P_(4) + 6Cl_(2) to 4PCl_(3)`
It is also obtained by the action of thionyl chloride with white phosphorus.
`P_(4) + 8SOCl_(2) to 4PCl_(3) + 4SO_(2) + 2S_(2)Cl_(2)`
Preparation of phosphorus pentachloride (`PCl_(5)`) : Phosphorus pentachloride is prepared by the reaction of white phosphorus with excess of dry chlorine.
`P_(4) + 10Cl_(2) to 4PCl_(5)`
It can also be prepared by the action of `SO_(2)Cl_(2)` on phosphorus:
`P_(4) + 10SO_(2)Cl_(2) to 4PCl_(5) + 10SO_(2)`
Phosphorus also forms trihalides with bromine and iodine however pentahalide with iodine is not known because of large size of iodine atom, the effective overlapping of orbitals donot take place to form a bond.