What is Phosphorus Pentoxide?
Phosphorus Pentoxide is a chemical compound whose empirical formula is P2O5 and whose molecular formula is P4O10. At ambient temperatures, this compound exists as a white solid that is crystalline in nature. Phosphorus pentoxide is an acid anhydride that is obtained from phosphoric acid. It is highly hygroscopic and is, therefore, used as a dehydrating agent and as a desiccant.
P2O5 (or P4O10) can be prepared by burning elemental P4 (tetra-phosphorus) in an environment containing a sufficient amount of oxygen. The chemical reaction for the preparation of P2O5 is provided below.
P4 + 5O2 → P4O10
This compound is a source of pure phosphoric acid.
Structure of Phosphorus Pentoxide
The structure of a phosphorus pentoxide molecule is illustrated below.
It can be noted that the P=O bond length in this compound is 143 picometers and the P-O bond length is 160 picometers.
Properties of Phosphorus Pentoxide
- Phosphorus pentoxide is a white solid which does not have any distinct odour.
- The chemical formula of this compound is P4O10. However, it is named after its empirical formula, which is P2O5.
- The molar mass of phosphorus pentoxide corresponds to 283.9 g/mol.
- The density of this solid is 2.39 g/cm3.
- The melting point of this P2O5 is 613K. Its boiling point corresponds to 633K (however, it undergoes sublimation at this temperature).
- Phosphorus pentoxide undergoes violent hydrolysis when exposed to water. This reaction is highly exothermic.
- This compound crystallizes in four different polymorphs.
- It is highly corrosive and must, therefore, be kept away from metals.
Uses of P2O5
- This compound is a very potent dehydrating agent (since it undergoes hydrolysis in an exothermic manner).
- Phosphorus pentoxide is also used in some organic synthesis reactions. For example, it is used in the preparation of nitriles from primary amides.
- It is a vital component of the Onodera reagent, which is widely used in the oxidation of alcohols.
- This compound can also be used to convert certain mineral acids into their anhydrides. For example, N2O5 can be prepared from HNO3 with the help of P2O5.
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