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# Phosphorus Pentachloride - PCl5

## What is Phosphorus Pentachloride?

Phosphorus pentachloride is a pale greenish-yellow solid with the formula PCl5.

Phosphorus pentachloride is known to have a salt-like structure in the crystalline state and to be partly dissociated in solution, especially in polar solvents such as nitrobenzene. It can be prepared by the action of dry chlorine on phosphorus trichloride.

As per the law of mass action, Phosphorus pentachloride vaporises almost without dissociation in an atmosphere of chlorine gas or phosphorus trichloride, the dissociation equilibrium is shifted to the left by the presence of the product.

Other names – Phosphorus(V) chloride, Pentachloro Phosphorane

 PCl5 Phosphorus Pentachloride Density 2.1 g/cm³ Molecular Weight/ Molar Mass 208.24 g/mol Boiling Point 166.8 °C Melting Point 160.5 °C Chemical Formula PCl5

## Physical Properties of Phosphorus Pentachloride – PCl5

 Odour Irritating odour Appearance Greenish-yellow crystalline solid Covalently-Bonded Unit 1 Molecular Geometry Trigonal bipyramid Complexity 37.1 Solubility Soluble in water

### Solid PCl5 Exists as

In the solid-state, PCl5 prefers to exist as oppositely charged ions like [PCl4]+ and [PCl6] as ionic bonding enhances the crystalline nature. The shape is more stable in the ionic form as it forms the tetrahedral and octahedral shapes.

## Chemical Properties of Phosphorus Pentachloride – PCl5

• Phosphorus pentachloride dissolves in water forming phosphoric acid and hydrogen chloride. The chemical reaction is given below.

PCl5 + 4H2O → H3PO4 + 5 HCl

• Phosphorus pentachloride reacts with sulphur dioxide to form phosphoryl chloride and thionyl chloride which is not a redox reaction. The oxidation states of elements did not change during the reaction.
$$\begin{array}{l}SO_{2} + PCl_{5} \rightarrow SOCl_{2} + POCl_{3}\end{array}$$

## Uses of Phosphorus Pentachloride – PCl5

• Used as a chlorinating agent and catalyst in making organic chemicals, intermediates, dyestuffs, etc.
• Used as a catalyst in the manufacture of acetyl cellulose, the plastic film on which motion pictures are printed.
• In the pharmaceutical industry it is used in the manufacturing of penicillin and cephalosporin.
• Used to produce acid chlorides and as a catalyst for cyclization and condensation reactions.

## Frequently Asked Questions – FAQs

### How is PCl5 is formed?

Phosphorus Penta chloride is prepared by passing an excess of dry chlorine into liquid trichloride. he chemical equation for the same is given as:

$$\begin{array}{l}PCl_{3}+ Cl_{2}(g)\to PCl_{5}\end{array}$$

### What are the uses of PCl5?

Used as a chlorinating agent and catalyst in making organic chemicals, intermediates, dyestuffs, etc. Used as a catalyst in the manufacture of acetyl cellulose, the plastic film on which motion pictures are printed.

### What happens when phosphorus pentachloride reacts with water?

Phosphorus pentachloride reacts vigorously with water to generate gaseous HCl. Based on a scenario where the chemical is spilled into an excess of water, half of the maximum theoretical yield of Hydrogen Chloride gas will be created in 0.54 minutes.

### Is PCl5 trigonal pyramidal?

PCl5 has the shape of a trigonal bipyramid and not a trigonal pyramid.

### Why is PCl5 more reactive?

In PCl5, in addition to equatorial bonds which lie in the same plane,there are axial bonds. Since axial bonds suffers more repulsion, they are longer than the other bonds. Also these are weak bonds and therefore these bonds can break easily . Because of these reasons,PCl5 is very reactive.

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