Equator Phosphorus is a chemical element with symbol P and atomic number 15. This word is made up of the Greek words phos (light) and foras (holder), which literally means holder of light. This phosphate is found in rocks. Its valency is 1, 3 and 5. In the periodic table of elements, it comes in the group of earth elements.
Phosphorus is a reactive element, hence it is not found in free state. Phosphates of metals are found in some minerals. 56% calcium phosphate is found in animal bones. It is an essential element for animals and plants. Its existence is found in many biological components. In 1669, Hamburg businessman Henning Brand discovered phosphorus.
There are 5 allotropes of phosphorus –
white or yellow phosphorus
White phosphorus is a soft waxy substance. It has a garlic like smell and when left in light it gradually turns yellow, that is why it is also called yellow phosphorus. Its melting point is 44.1 C and boiling point is 280.5 C. It is insoluble in water and soluble in carbon disulfide (CS2). It is a poisonous substance.
When white phosphorus is heated at 250°C in the presence of nitrogen or carbon dioxide gas, it gets transformed into red phosphorus. It is a red colored solid substance whose density is 2.5 and boiling point is 582. By vaporizing it in the presence of Ti2/N2 or Ps2/CO2 gas at 550 degree centigrade and suddenly cooling it, it gets transformed back into white phosphorus.
Apart from this, other alloforms of phosphorus are not important.
Phosphorite powder is prepared by heating it with sand and coke in an electric furnace at 1000°C. Calcium silicate comes out as slag –
Ca3(PO4)2 → 3CaSiO3 + P2O5
P2O5 + 5C → 2P+ 5CO
Properties of phosphorus
By reacting with respiratory air it forms two types of oxides –
4P + 3O2 → 2P2O3
4P + 5O2 → 2P2O5
Which shows that phosphorus has both 3 and 5 valency. Similarly, by reacting with chlorine it also forms two types of chlorides –
2P + 3Cl2 → 2PCl3
2P + 5Cl2 → 2PCl5
Phosphine gas is produced when white phosphorus is heated with caustic soda (NaOH) –
4P + 3NaOH → 3NaH2PO2 + PH3
When white phosphorus is kept in a dark room, light can be seen emanating from it, which comes out as a result of its slow combustion. This property is called phosphorescence.
Earlier phosphorus was obtained from animal bones. In this method, after reacting gelatin-free or roasted bones with sulfuric acid in a big tank, the liquid is filtered and evaporated. And when the relative density of this liquid becomes 1.45, then 20% coal or burnt stone coal (coke) is added to it and it is heated in shallow pans. When six percent moisture remains in it, then it is kept in closed mouth vessels and heated in the furnace till it turns red. In this way, by continuously heating for three to four days, the present phosphorus gets distilled and gets collected in water in another vessel, from where it is taken out and re-distilled, then pure phosphorus is obtained. But this is a very painful method. Even at high cost, very little phosphorus is obtained from it; Therefore, now electric furnaces and air furnaces have started being used and commercial manufacturing of phosphorus has also become easy and cheap. In this new system, a mixture of rock phosphate, silica and carbon (coke) is melted in a furnace in a reducing environment and then the phosphorus vapor is collected and converted into various types of compounds. In this method, sulfuric acid is not required and more phosphorus is also obtained from it.