What is P4O10?

What is P4O10? P4O10 is named phosphorus pentoxide. Its molecular formula is P4O10 and the empirical formula is P2O5. The name of the compound is generally taken from its empirical formula and hence named phosphorus pentoxide. P4O10 has a physical form of white crystalline powder and very deliquescent.

Structure of P4O10

Phosphorus pentoxide (P4O10) exists in four crystalline forms that are referred to as polymorphs of phosphorus pentoxide. The most important form is metastable polymorph having formula P4O10 that is phosphorus pentoxide.

Van der Waals forces

  • Forces of attraction present in the polymorphs that keep the molecules together are van der Waals forces. In contrast to the typical crystals, the crystal packing is not close although it’s highly symmetrical.

  • The structure of P4O10 is related to the anhydrides of phosphorus acid (P4O6). Phosphorus acid doesn’t have the oxo groups and has a density of 2.3 g/cm3. Its boiling point is at 423.0 °C and if heated abruptly, sublimation can occur.

Phosphorus acid preparation

  • The phosphorus acid can be obtained by condensation of the vapors of phosphorus pentoxide. The resultant compound obtained after the condensation is a solid that is highly hygroscopic.

  • Other polymorphic forms are the polymers but, in all polymers, phosphorus atoms are linked with oxygen atoms in a tetrahedral form.

Macromolecular form

  • If the compound (P4O10) is heated in a closed tube for many hours and the molten form is maintained at an increased temperature that inhibits the cooling of the compound, the macromolecular structure is obtained.

1. Orthorhombic form

  • This slightly stable orthorhombic form with a density of 2.7 g/cm3 and a melting temperature of 562.0°C then makes layers and that layered form contains interrelated rings of P6O6 rings.

2. Stable form

  • The stable form has a high density as compared to the metastable form. Moreover, it has an orthorhombic structure and a three-dimensional form with a density of 3.5 g/cm3. The rest of the polymorph has either glass or amorphous form, it can be made by melting any other form.

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Properties of P4O10

Phosphorus pentoxide (P4O10) is a chemical compound that is a dehydrating agent and has an excessively corrosive nature. General properties of phosphorus pentoxide (P4O10) have been tabulated below:

:one: Name Phosphorus pentoxide
:two: Another name Phosphorus oxide diphosphonate
:three: Molecular formula P4O10
:four: Empirical formula P2O5
:five: Melting point 613 K
:six: Boiling point 360 °C
:seven: Molecular weight 141.922 g/mole
:eight: Physical form Dry powder, deliquescent
:nine: Isotopes :x:
:keycap_ten:Density 2.4 g/cm3

How can P4O10 be prepared?

Phosphorus pentoxide (P4O10) is synthesized by burning the phosphorus with enough amount of oxygen. It generates the following chemical equation:

P4 + 5 O2 → P4O10

1. Thermal process

Mostly during the 20th century, the P4O10 has been used to produce the concentrated phosphoric acid by a thermal process. In this process, the P4O10 that is obtained by burning white phosphorus was dissolved in dilute phosphorus acid to produce concentrated acid.

2. Wet process

With the advent of time, as the filtration technology has been advanced, so now the modern processes are replacing the old ones. Wet-process phosphoric acid is now a trending product in which the initializing ingredient is white phosphorus.

3. Phosphoric acid dehydration

Although dehydration of the phosphoric acid can lead to phosphorus pentoxide, yet is impossible to perform and obtain P4O10 because the heating will induce boiling before the dehydration.

Phosphorus pentoxide and water

As far as the question is concerned about reaction of P4O10 with water after the understanding that what is P4O10? Phosphorus pentoxide (P4O10) reacts vigorously with water and undergoes hydrolysis. This hydrolysis process generates heat and phosphoric acid.

1. Contact with the body surface

If the reaction between water and P4O10 occurs at the body surface, the generation of HCl and H2SO4 may cause corrosion of the skin. Signs and symptoms of P4O10 corrosion are:

  • Extreme irritation
  • Skin redness
  • Severe burns and pain

2. Inhalation of P4O10

  • If phosphorus pentoxide (P4O10) is inhaled by a person, it can impart severe damage to the mucous membrane and respiratory pathway.

  • Signs and symptoms of this damage may be including the irritated nose and throat majorly being the forced respiration.

  • Inhalation of phosphorus pentoxide may lead to pulmonary edema that requires emergency treatment immediately.

3. Ingestion of P4O10

As phosphorus pentoxide is highly corrosive when comes in contact with moisture either on the external body surface or internal. It leaves a burning effect on the mucosa of the digestive tract with serious signs and symptoms. Signs and symptoms of corrosion by phosphorus pentoxide may involve the following:

  • Pain in throat

  • Severe body pain

  • Nausea, vomiting, and diarrhea

  • Brownish and yellowish marks around the mouth

  • Macroglossia (swollen tongue) leading to difficult breathing

  • Chemical induced pneumonia if aspired to lungs

  • May lead to death

4. Reactions of P4O10 to eyes

Vapors and powdered particles of phosphorus pentoxide impart corrosive reactions to the eyes if come in contact. It may burn or permanently damage the eyes.

5. Long term exposure to P4O10

If phosphorus pentoxide is ingested or inhaled for longer durations, it may cause irreversible damage to internal systems due to its corrosive nature. It is referred to as phosphate poisoning and can cause the following abnormalities:

  • Hepatic injury

  • Renal injury

  • Hematic disorders

  • Heart problems

  • Abnormalities of the oral cavity including jaws and teeth

In short :writing_hand:
Phosphorus pentoxide (P4O10) is a chemical compound that is vastly used as a dehydrating agent. It has a corrosive nature when comes in contact with water and damages surface and mucus membranes if inhaled, touched, or ingested.

P4O10 ionic or covalent?

  • To understand whether phosphorus pentoxide is ionic or covalent, we must look into the bonds that the atoms are making with each other and the chemical nature of elements that are present in the compound.

  • As phosphorus and oxygen both are non-metallic elements and both are bound together by covalent bond, hence it is obvious that phosphorus pentoxide has a covalent nature.

  • Moreover, upon hydrolysis, there is no ionic specie generated which is another indication of the covalent nature of phosphorus pentoxide.

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Uses of phosphorus pentoxide

Phosphorus pentoxide (P4O10) is mainly and vastly used as drying as it reacts with water molecules and produces phosphoric acid with a lot of heat production.

1. Dehydrating agent

It is used as granules to be used as a dehydrating agent. The exothermic nature of phosphorus pentoxide (P4O10) while reacting with water or moisture is its real capability to act as a dehydrating agent. Reaction with water can be given as:

P4O10 + 6 H2O → 4 H3PO4 (–177 kJ)

  • While minus sign shows that the reaction is exothermic and the value 177 kJ indicates the amount of heat released during the reaction.

  • Phosphoric acid that is produced as a product of hydrolysis is also a hygroscopic compound that further absorbs the moisture.

  • Dehydrating capacity is less because of the formation of a protective coating that hinders the further reaction.

For example

Dehydration of amide compounds to produce nitriles is performed by phosphorus pentoxide. Other uses of phosphorus pentoxide are listed below:

2. Acts as initiating material

Phosphorus esters that are utilized as surfactants and extraction reactions are prepared by using phosphorus pentoxide as the starting material.

3. P4O10 as a synthetic agent

Phosphorus pentoxide (P4O10) is used as a synthetic agent for several pharmaceutical agents and pesticide compounds.

4. Synthesis of glass

One of the important uses of phosphorus pentoxide (P4O10) is that it is used in the manufacturing of optical and heat resistant glass.

Summary :writing_hand:
Phosphorus pentoxide is the dehydrating compound and has a corrosive nature when undergoes hydrolysis. It is used as a drying agent, starting material in various reactions and in the synthesis of glass.

Why is phosphorus pentoxide named so?

  • The molecular formula of the compound is P4O10.it can be simplified by converting it to an empirical formula.

  • A molecular formula expresses the total number of molecules that are forming the compound while the empirical formula is the simplest whole-number ratio of atoms in a compound.

  • The name of the compound is mostly inferred from its empirical formula and the same is in the case of phosphorus pentoxide.

  • As there are 5 oxygen atoms in the empirical formula of phosphorus pentoxide hence the name “pentoxide”.

Hazards of P4O10

  • After discussing that what is P4O10, now its the time to talk about it’s hazards. Phosphorus pentoxide (P4O10) is not combustible by its self. It undergoes a strong reaction when comes in contact with water, moisture, or any other water containing agents such as cotton.

  • This reaction generates a lot of heat and hence an exothermic reaction. If the reactions occur at the body tissues when it comes in contact with skin, it can cause skin burns, damage to eyes, and mucous membranes.

Frequently asked questions

The chemical study is such a large topic that there are a lot of questions popping out in one’s mind when it’s concerned about phosphorus pentoxide. Some of them have been answered below:

1. Why P4O10 is phosphorus pentoxide?

  • Phosphorus pentoxide is the dehydrating agent with a molecular formula of P4O10 which is simplified to generate empirical formula P2O5.

  • Mostly, the name of a compound is inferred from its empirical formula and the empirical formula of phosphorus pentoxide is P2O5. This is the reason for giving the name phosphorus pentoxide.

2. Is P4O10 acidic or basic?

  • Phosphoric pentoxide P4O10 is acidic. To elaborate that what is P4O10, it is a chemical compound with a large capability of dehydration. Another striking property of phosphorus pentoxide is its corrosive nature.

  • When phosphorus pentoxide P4O10 undergoes hydrolysis, it generates phosphoric acid and causes the corrosion of body tissues. Moreover, it reacts vigorously with bases and hence it indicates the acidic nature of P4O10.

3. How P4O10 is formed?

  • Phosphorus pentoxide (P4O10) is synthesized by the burning of phosphorus in an excess amount of oxygen. It’s a white-colored, crystalline powder and used vastly as a dehydrating agent.

  • P4O10 is obtained when water is eliminated from H3PO4 and undergoes hydrolysis when comes in contact with water. This hydrolysis generates a lot of heat and phosphoric acid.

  • Phosphoric acid hence produced is also hygroscopic and absorbs remaining moisture.

4. What happens when phosphorus reacts with oxygen?

  • Phosphorus undergoes a reaction with molecular oxygen and generally produces two types of oxides. Oxide production depends upon the availability of oxygen.

  • When oxygen is present in a limited amount, the oxide that is produced is P4O6. When oxygen is present in ample amount, then P4O10 is generated that is named as phosphorus pentoxide P4O10.

  • However, both of these oxides react with water and undergo hydrolysis to produce oxoacids.

5. Why is phosphorus called Devil’s element?

  • Brand, who was the discoverer of phosphorus, discovered it as a white powder, that undergoes a reaction with oxygen present in the air. This reaction produces the greenish-white colored light.

  • Some may think that the emission or production of that light is due to the process of phosphorescence but it can’t be phosphorescence.

  • According to a few texts, the phosphorus element is known as the devil’s element because of this strange and frightening light.


  • What is P4O10? It is a common question related to chemistry. P4O10 is known as phosphorus pentoxide and the name is inferred from its empirical formula that is P2O5.

  • Phosphorus pentoxide P4O10 is used as a strong dehydrating agent and used as a desiccant in the granular form.

  • Being highly corrosive, phosphorus pentoxide P4O10 when comes in contact with the water an exothermic reaction occurs with the generation of heat and phosphoric acid.


Phosphorus pentoxide | chemical compound | Britannica
Phosphorus Pentoxide - an overview | ScienceDirect Topics

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