Phosphorus Pentachloride

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What is Phosphorus Pentachloride?

Phosphorus pentachloride is a greenish-yellow crystalline solid, It is decomposed by water to form hydrochloric acid and phosphoric acid with the release of heat energy. It can also be prepared by the action of dry chlorine on phosphorus trichloride. The chemical formula for phosphorus pentachloride is PCl₅. In solid-state, it exists as [PCl₄]⁺ [PCl₆]⁻ .


Phosphorus pentachloride vaporizes without dissociation in an atmosphere phosphorus trichloride or chlorine gas. The dissociation equilibrium is shifted to the left side by the presence of the product.


Structure of Phosphorus Pentachloride

The hybridization in phosphorus pentachloride is sp³d and it has a trigonal bipyramidal geometry in gaseous and liquid states. It has two axial P−Cl bonds and three equatorial P−Cl bonds.

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Properties of Phosphorus Pentachloride

Formula of phosphorus pentachloride

PCl₅

Molecular Weight

208.24 g/mol

Density

2.1 g/cm³

Melting Point

160.5 ⁰C

Boiling Point

166.8 ⁰C

phosphorus pentachloride shape

Trigonal bipyramid

Odour

Irritating odour


Uses of Phosphorus Pentachloride (PCl₅)

  • It is used as a chlorinating agent.

  • It is used for the manufacture of penicillin and cephalosporin in the pharmaceutical industry.

  • Used to produce acid chlorides. 

  • Used as a catalyst in the manufacture of acetyl cellulose and also a catalyst for condensation reactions and cyclization.

Methods of Preparation of Phosphorus Pentachloride (PCl₅)

  • P₄ + 10SO₂Cl₂ → 4PCl₅ + 10SO₂ 

  • P₄ + 10Cl₂ → 4PCl₅

  • PCl₃ + Cl₂ → PCl₅

Chemical Properties of Phosphorus Pentachloride (PCl₅)

  • Phosphorus pentachloride dissociates as: PCl₅ ⇌ PCl₃ + Cl₂

  • Reaction with water: PCl₅ + 4H₂O → H₃PO₄ + 5HCl

  • Reaction with metal: Zn + PCl₅ → ZnCl₂ + PCl₃

  • Reactions with phosphorus pentoxide: 6PCl₅ + P₄O₁₀ → 10POCl₃ 

  • Reactions with sulfur dioxide: SO₂ + PCl₅ → POCl₃ + SOCl₂ 

Harmful Effects of Phosphorus Pentachloride

Phosphorus Pentachloride is a Reactive Chemical. Direct exposure to Phosphorus Pentachloride can cause weakness, nausea, headache, dizziness, and vomiting. It may damage the liver and kidneys.

FAQ (Frequently Asked Questions)

Question: Why PCl₅ Has Trigonal Bipyramidal Shape Whereas IF₅ Is the Square Pyramidal in Shape?


Answer: In PCl₅ P atom is surrounded by 5 bond pairs and has no lone pairs in it, On the other hand in IF₅, the iodine atom is surrounded by 5 bond pairs and one lone pair, therefore the shape is different in both cases. Also, the hybridization in PCl₅ is sp³d and in IF₅ it is sp³d².

Note: The lone pair - lone pair causes maximum repulsion than lone pair-bond pair repulsion,

And lone pair-bond pair repulsion is more than bond pair-bond pair repulsion.

Question: PCl₅ -  is it Acidic or Basic in Nature?

Answer:  Phosphorus Pentachloride PCl₅ contain empty d orbitals in the valence shell. Hence it can act as Lewis acid. (According to Lewis’s concept of acid, It is the substance with an empty orbital in a valence shell so that it can accept electron pairs.

Question: What Happens When PCl₅ is Heated?

Answer: When Phosphorus pentachloride (PCl₅) is heated, It will decompose into phosphorus trichloride(PCl₃) and chlorine gas (Cl₂). If placed in water, it will form phosphoric acid (H₃PO₄) and hydrochloric acid (HCl) with the release of heat energy.