Phosphine, Phosphorus Trichloride, Phosphorus pentachloride

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, PH3 Phosphorus Trichloride, PCl3 Phosphorus pentachloride, PCl5
Explain Phosphine 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
Preparation Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.
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
Properties It 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

Property Phosphine Ammonia
Colour Colourless Colourless
Decomposition by electric spark Decomposes into elements Decomposes into elements
Action with chlorine Reacts violently to form PCl5 Reacts with chlorine to form nitrogen trichloride
Action with halogen acids Forms phosphonium salts Forms ammonium salts
Combustibility Burns in air to form phosphoric acid Burns in air to form nitrogen and water.
Smell Unpleasant smell of rotten fish. Characteristic ammoniacal smell.
Density Heavier than air Lighter than air
Solubility Sparingly soluble in water Highly soluble in water
Nature Highly poisonous Non- poisonous
Action towards Neutral Basic
Stability Less stable More stable
Stability of salts Less More


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