Phosphorus was discovered and isolated in 1669 by the German chemist J. Brand.In nature, this element occurs only in the form of compounds.The main minerals - phosphorite Ca3 (PO4) 2 and apatite 3Ca3 (PO4) 2 • CaF2 or Ca5F (PO4) 3.Furthermore, the element part of the protein, and is also found in teeth and bones.Phosphorus is most easily reacts with oxygen and chlorine.With an excess of these substances are formed compounds in the oxidation state (for P) +5, and with a lack of - with the +3 oxidation state.Phosphorus oxide can be represented by several formulas, display different chemicals.Among them, the most common - it P2O5 and P2O3.Other rare and little known oxides are: P4O7, P4O8, P4O9, PO and P2O6.
The oxidation of elemental phosphorus oxygen is slow.Interesting its various aspects.Firstly, in the dark, luminescence can be clearly seen that it is accompanied.Secondly, the process of oxidation of the chemical always occurs to form ozone.This is due to afford intermediate - phosphoryl PO - scheme: P + PO + O2 → O, then: O + O2 → O3.Thirdly, the oxidation due to the sharp change in the conductivity of the ambient air due to its ionization.Isolation of light without significant reheating, when chemical reactions, called chemiluminescence.In humid environments, green chemiluminescence due to the formation of the intermediate PO.
phosphorus oxidation occurs only at a certain concentration of oxygen.It should not be below the minimum and above the maximum thresholds of the partial pressure of O2.Himself interval depends on temperature and other factors.For example, under standard conditions, the rate of oxidation reaction of phosphorus pure oxygen increases until reaching 300 mmHg.Art.It then decreases and drops to nearly zero when oxygen partial pressure reaches 700 mm Hg.Art.and higher.Thus, under normal conditions of oxide is formed, since phosphorus is hardly oxidized.
phosphorus pentoxide
most typical oxide is phosphorus pentoxide or higher oxides of phosphorus, P2O5.It is a white powder with a pungent odor.When determining in pairs of its molecular weight, it was found that a proper record is its formula P4O10.This incombustible material, it melts at 565.6 C. The anhydride -kislotny P2O5 oxide, with all the characteristic properties, but it is avidly absorbed moisture, so is used as a desiccant for liquids or gases.Phosphorus oxide can take water that is part of the chemical.The anhydride is formed by the combustion of phosphorus in oxygen or air, a sufficient amount of O2 under the scheme: 4P + 5O2 → 2P2O5.It is used in the production of acid H3PO4.In contact with water may form a three acid:
- metaphosphoric: P2O5 + H2O → 2HPO3;
- pyrophosphoric: P2O5 + 2H2O → H4P2O7;
- orthophosphoric: P2O5 + 3H2O → 2H3PO4.
phosphorus pentoxide reacts violently with water and substances containing water, such as wood or cotton.This produces a lot of heat, which can even lead to a fire.It is corrosive to metals and very annoying (there are serious burns to eyes, skin) and respiratory mucous membranes, even at concentrations as low as 1 mg / m³.
trioxide phosphorus
Phosphorous anhydride or phosphorus trioxide, P2O3 (P4O6) - is a white crystalline solid (looks like a wax), which melts at a temperature of 23.8 C and boils at 173.7C. As white phosphorus, P2O3 is very poisonous.It is an acidic oxide, with all its 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 deficiency of oxygen.Phosphorus trioxide reacts slowly with cold water to form acid: P2O3 + 3H2O → 2H3PO3.This phosphorus oxide reacts vigorously with hot water, and the reactions occur differently, resulting in red phosphorus can be formed (modified allotropic podukt), phosphorus hydride and acid: H3PO3 and H3PO4.Thermal decomposition is accompanied by cleavage of the anhydride P4O6 phosphorus atoms, wherein the mixed oxides are formed P4O7, P4O8, P4O9.According to the structure, they resemble P4O10.The most studied of them P4O8.
