Phosphorus was discovered and isolated in 1669 by the German chemist H. Brand. In nature, this element is found only in the form of compounds. The main minerals are phosphorite Ca3 (PO4) 2 and apatite 3Ca3 (PO4) 2 • CaF2 or Ca5F (PO4) 3. In addition, the element is part of proteins, and also found in teeth and bones. Phosphorus most easily interacts with oxygen and chlorine. With an excess of these substances, compounds with an oxidation state (for P) of +5 are formed, and with a deficiency, compounds with an oxidation state of +3. Phosphorus oxide can be represented by several formulas that display different chemicals. Among them, the most common are P2O5 and P2O3. Other rare and poorly studied oxides include: P4O7, P4O8, P4O9, PO and P2O6.
The oxidation of elemental phosphorus with oxygen proceeds slowly. Its various sides are interesting. Firstly, in the dark you can clearly see the glow with which it is accompanied. Secondly, the oxidation of this chemical always occurs with the formation of ozone. This is due to the preparation of an intermediate compound — phosphoryl PO — according to the scheme: P + O2 → PO + O, and then: O + O2 → O3. Thirdly, oxidation is associated with a sharp change in the electrical conductivity of the surrounding air due to its ionization. The release of light without noticeable heating, during chemical reactions, is called chemiluminescence. In humid environments, green chemiluminescence is due to the formation of an intermediate, PO.
Oxidation of phosphorus occurs only at a certain oxygen concentration. It should not be lower than the minimum and above the maximum thresholds of the partial pressure O2. The interval itself depends on temperatures and a number of other factors. For example, under standard conditions, the rate of oxidation of pure phosphorus oxygen increases to reach 300 mm Hg. Art. Then it decreases and drops to almost zero when the partial pressure of oxygen reaches 700 mm Hg. Art. and higher. Thus, the oxide does not form under ordinary conditions, since phosphorus is practically not oxidized.
Phosphorus pentoxide
The most characteristic oxide is phosphoric anhydride, or higher phosphorus oxide , P2O5. It is a white powder with a pungent odor. When determining its molecular weight in pairs, it was found that P4O10 is a more correct record of its formula. This non-combustible substance, it melts at a temperature of 565.6 ° C. P2O5 anhydride is an acid oxide with all its characteristic properties, but it eagerly absorbs moisture, therefore it is used as a desiccant for liquids or gases. Phosphorus oxide can take away water, which is part of chemicals. Anhydride is formed as a result of the combustion of phosphorus in an atmosphere of oxygen or air, with a sufficient amount of O2 according to the scheme: 4P + 5O2 → 2P2O5. It is used in the production of H3PO4 acid. When interacting with water, it can form three acids:
- metaphosphoric: P2O5 + H2O → 2HPO3;
- pyrophosphoric: P2O5 + 2H2O → H4P2O7;
- phosphoric: P2O5 + 3H2O → 2H3PO4.
Phosphorus pentoxide reacts violently with water and substances containing water, such as wood or cotton. This generates a large amount of heat, which can even lead to a fire. It causes metal corrosion and is very annoying (severe burns to the eyes, skin) of the respiratory tract and mucous membranes, even at such low concentrations as 1 mg / m³.
Phosphorus trioxide
Phosphorous anhydride, or phosphorus trioxide, P2O3 (P4O6) is a white crystalline substance (looks like wax) that melts at a temperature of 23.8 C and boils at a temperature of 173.7 C. Like white phosphorus, P2O3 is a very toxic substance . It is an acid oxide with all its inherent properties. Phosphorus oxide 3 is formed due to the slow oxidation or combustion of the free substance (P) in an environment where there is a lack of oxygen. Phosphorus trioxide slowly interacts with cold water to form an acid: P2O3 + 3H2O → 2H3PO3. This phosphorus oxide reacts vigorously with hot water, and the reactions proceed differently, resulting in the formation of red phosphorus (an allotropically modified product), phosphorus hydride, and also acids: H3PO3 and H3PO4. The thermal decomposition of P4O6 anhydride is accompanied by the removal of phosphorus atoms, and mixtures of P4O7, P4O8, P4O9 oxides are formed. In structure, they resemble P4O10. The most studied of them is P4O8.