While the compound P4O10 has many names, its most common name is phosphorus pentoxide. This compound is made up of four phosphorus atoms and 10 oxygen atoms bonded together with covalent bonds.
How Was P4O10 Named?
The name may be confusing to some, since the prefix "pent-" refers to five, and there are 10 oxygen atoms in the compound. Phosphorus pentoxide gets its name from the empirical formula of the compound, which is P2O5. Molecules of P2O5 are unstable and associate with each other to form the larger molecules of P4O10.
Physical Properties of P4O10
At room temperature, phosphorus pentoxide is a solid, white waxy substance and is typically a powder. The molecule has a hexagonal shape and is held together with weak van der Waals forces. This compound is unique in that it exists in four different polymorphs. The most common is two molecules of P2O5 joined together to form the larger P4O10. All of phosphorus pentoxide's polymorphs are based around the tetrahedral arrangement of the phosphorus and oxygen atoms make up the compound.
It melts at 340C and boils at 360C. Because the melting point and boiling points are so close together, phosphorus pentoxide often skips melting and sublimates from solid to gas.
Chemical Properties of P4O10
Phosphorus pentoxide is a polar compound. It is a noncombustible compound, meaning that it does not react with oxygen to produce a flame. However, it is highly reactive with water and forms phosphoric acid when combined with water. It can cause a fire if it comes in contact with water-containing materials, such as cotton or wood. When exposed to metal, it causes corrosion and forms various metal oxides. It's also corrosive to skin and other tissues, leading to chemical burns and respiratory inflammation. These irritations and injuries occur even in small concentrations. Proper safety measures are required when handling phosphorus pentoxide.
Production of P4O10
Phosphorus pentoxide is typically produced through the combustion of phosphorus and oxygen. Burning tetraphosphorus with a large amount of oxygen produces the compound. White phosphorus is necessary as the starting material. Although adding water to phosphorus pentoxide produces phosphoric acid, the reaction does not work in reverse. It's not possible to produce phosphorus pentoxide by dehydrating phosphoric acid.
Uses for P4O10
Phosphorus pentoxide is commonly used in the production of phosphoric acid. Because it reacts so easily with water, it's also used as a desiccant and dehydrating agent. It draws moisture out of the air to keep an area free from moisture. Phosphorus pentoxide has a tendency to form a protective layer around the outside during storage, which prevents it from drawing in any more moisture. Because of this, it's often used in its granular form for drying.
As an industrial desiccant, this compound plays an intermediate role in turning acids into their anhydride counterparts. For example, it's used to convert nitric acid (HNO3) into nitrogen pentoxide (N2O5). Phosphorus pentoxide is also used in the manufacture of glass, rubber, and some laboratory procedures.
Other Names for P4O10
While phosphorus pentoxide is the most common name for P4O10, it does go by other names, including:
- Diphosphorus pentoxide
- Phosphorus(V) oxide
- Phosphoric anhydride
- Tetraphosphorus decaoxide
- Tetraphosphorus decoxide