Phosphorus Oxide
Phosphorus was discovered and isolated in 1669 by the Germanchemist H. Brand. In nature, this element occurs 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 the protein, and also contained in the teeth and bones. Phosphorus most easily interacts with oxygen and chlorine. With an excess of these substances, compounds with an oxidation degree (for P) +5, and in case of a deficiency, with a degree of oxidation +3, are formed. Phosphorus oxide can be represented by several formulas that represent different chemical substances. Among them, the most common are P2O5 and P2O3. Other rare and poorly studied oxides are: P4O7, P4O8, P4O9, PO and P2O6.
The reaction of oxidation of elemental phosphorusoxygen flows slowly. Its various aspects are interesting. Firstly, in the dark, the glow that accompanies it is clearly visible. Secondly, the oxidation of this chemical always occurs with the formation of ozone. This is due to the preparation of the intermediate - phosphoryl PO - according to the scheme: P + O2 → PO + O, and then: O + O2 → O3. Third, oxidation is associated with a sudden change in the electrical conductivity of the ambient air due to its ionization. The release of light without noticeable heating, when chemical reactions occur, is called chemiluminescence. In wet environments, green chemiluminescence is caused by the formation of an intermediate substance PO.
Oxidation of phosphorus occurs only whena certain concentration of oxygen. It must not be below the minimum and above the maximum thresholds for 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 by pure oxygen of phosphorus increases to 300 mm Hg. Art. Then it decreases and falls almost to zero, when the oxygen partial pressure reaches 700 mm Hg. Art. and higher. Thus, oxide under normal conditions is not formed, since phosphorus is practically not oxidized.
Phosphorus pentoxide
The most typical oxide is phosphoricanhydride, or higher phosphorus oxide, P2O5. It is a white powder with a pungent odor. When determining its molecular weight in pairs, it is established that the more correct record of its formula is P4O10. It is a non-flammable substance, it melts at a temperature of 565.6 ° C. Anhydride P2O5 is an acid oxide with all the characteristic properties, but it greedily absorbs moisture, so it is used as a dehumidifier for liquids or gases. Phosphorus oxide can take away water, which is a part of chemical substances. 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, three acids can form:
- Metaphosphoric: P2O5 + H2O → 2HPO3;
- pyrophosphoric: P2O5 + 2H2O → H4P2O7;
- orthophosphoric: P2O5 + 3H2O → 2H3PO4.
Phosphorus pentoxide reacts violently with water andsubstances containing water, such as wood or cotton. This generates a large amount of heat, which can even lead to a fire. It causes corrosion of the metal and is very irritating (serious burns to the eyes, skin), respiratory tract and mucous membranes, even at concentrations as low as 1 mg / m³.
Phosphorus trioxide
Phosphorous anhydride, or phosphorus trioxide, P2O3(P4O6) is a white crystalline substance (superficially similar to wax), which melts at 23.8 ° C and boils at a temperature of 173.7 ° C. Like white phosphorus, P2O3 is a very poisonous substance. It is an acidic oxide, with all the inherent properties. Phosphorus oxide 3 is formed due to the slow oxidation or combustion of the free substance (P) in a medium where there is a lack of oxygen. Phosphorus trioxide slowly reacts with cold water, forming an acid: P2O3 + 3H2O → 2H3PO3. This phosphorus oxide reacts vigorously with hot water, the reactions proceeding in different ways, as a result, red phosphorus (an allotropically modified product), phosphorus hydride, and also acids: H3PO3 and H3PO4. Thermal decomposition of P4O6 anhydride is accompanied by the splitting off of phosphorus atoms, and mixtures of oxides P4O7, P4O8, P4O9 are formed. In structure, they resemble P4O10. The most studied of them is P4O8.
