Phosphine, Phosphorus Trichloride, Phosphorus pentachloride

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chemistry 12th class cbse notes

Phosphorus forms two types of halides, PX3 (X = F, Cl, Br, I) and PX5 (X = F, Cl, Br).

  1. Phosphorus trichloride, PCl3
  2. Phosphorus pentachloride, PCl5

Phosphine, PH3Phosphorus Trichloride, PCl3Phosphorus pentachloride, PCl5
ExplainPhosphine is a highly poisonous, colourless gas and has a smell of rotten fish.This is a type of halides.
It is a colourless oily liquid.
It is molecular in gas and liquid phase, but in solid state exists as [PCl4]+  PCl6] containing tetra and hexa-coordinated phosphorous species.
Phosphorus pentachloride
PreparationPhosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.
Phosphine
It is obtained by passing dry chlorine over heated white phosphorus or by the action of thionyl chloride with white phosphorus.
Phosphorus Trichloride
Phosphorus pentachloride is prepared by the reaction of white phosphorus with excess of dry chlorine or can be prepared by the action of SO2Cl2 on phosphorus.
Phosphorus pentachloride
PropertiesIt is insoluble in water and is a weaker base than ammonia. Like ammonia, it gives phosphonium compounds with acids. For example:
PhosphinePH3 is non-inflammable when pure but becomes inflammable owing to the presence of P2H4 or P4 vapours.
In water, PH3 decomposes in the presence of light to give red phosphorus and H2.
It has a pyramidal shape, in which phosphorus is sp3 hybridised.
It gets hydrolysed in the presence of moisture.
Phosphorus Trichloride
In gaseous and liquid phases, its has a trigonal bipyramidal structure.Phosphorus pentachloridePCl5 is a yellowish white powder and in moist air, it hydrolyses to POCl3 and finally gets converted to phosphoric acid.Phosphorus pentachlorideWhen heated, it sublimes but decomposes on stronger heating.

Phosphorus pentachloride

Comparison between Phosphine and Ammonia


PropertyPhosphineAmmonia
ColourColourlessColourless
Decomposition by electric sparkDecomposes into elementsDecomposes into elements
Action with chlorineReacts violently to form PCl5Reacts with chlorine to form nitrogen trichloride
Action with halogen acidsForms phosphonium saltsForms ammonium salts
CombustibilityBurns in air to form phosphoric acidBurns in air to form nitrogen and water.
SmellUnpleasant smell of rotten fish.Characteristic ammoniacal smell.
DensityHeavier than airLighter than air
SolubilitySparingly soluble in waterHighly soluble in water
NatureHighly poisonousNon- poisonous
Action towardsNeutralBasic
StabilityLess stableMore stable
Stability of saltsLessMore

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