white phosphorus: Preparation, Properties, Structure, and uses

White Phosphorus

Phosphorus is a catalytic element. It is easily oxidized by the presence of oxygen in the air. Therefore, it is not found in an independent state. In nature, it is found mainly in its phosphate compounds(PO₄^3-). Some of the main minerals in which Phosphorus is present.

Phosphorus is an essential component of all organisms. Phosphorus is a major component of bones and teeth in the form of calcium phosphate (Ca₃(PO₄)₂).

Phosphorus Preparation:

Phosphorus is mainly made from the bone-ashes or Phosphate Rock. There are two main methods of making Phosphorus from bone-ashes or Phosphate Rock.

1. Retort Process
2. Electrothermal Process

Retort process is the old method and Electrothermal Process is the modern method. Both of these methods give white Phosphorus and Phosphorus.

Retort Process

In this method, heats the fine powder of bone ash or phosphorite with sulfuric acid. On doing this, orthophosphoric acid and Calcium sulfate are formed.

Ca₃(PO₄)₂ + 3H₂SO₄ → 2H₃PO₄ + 3CaSO₄↓

Continuous Calcium Sulfate is filtered and taken apart. And the filtered solution evaporates, converting orthophosphoric acid into Meta phosphoric acid. It is heated in a soil made of fireproof Retort with coke.

Meta phosphoric acid is reduced by coke to form phosphorus. The phosphorus evaporates and begins to exit from the retort. These vapors flow into the water and cool it, which makes the phosphorus collect as a solid on the lower surface in the water.

H₃PO₄ → HPO₃ + H₂O

4HPO₃ + 10C → 4P (P₄) +10CO + 2H₂O

Electrothermal Process:

In this method, the fine powder of Bone-ash or phosphorus is mixed with coke and sand and heated in an electric furnace. In the electric furnace, this mixture is slowly poured from the top with the help of a rotating screw. The electric furnace generates high heat (1500-3500⁰C) by generating an electric arc between two carbon electrodes.

Ca₃(PO₄)₂ + 3SiO₂ → 3CaSiO₃ + P₂O₅

P₂O₅ + 5C → 2P + 5CO

Calcium Silicate accumulates in the form of a slag under the reactors in the electric furnace. Which is removed in due course of the exit gate.

The phosphorus made of the agent evaporates out of the furnace by the drainage. The phosphorus is cooled by caring for it in water. In this way, phosphorus gets deposited at the bottom of the pot filled with water.

Purification of Phosphorus:

The phosphorus obtained from the above methods has some impurities. To remove them, impure phosphorus is heated lightly with a dilute solution of acidic potassium dichromate. By doing this the impurities get oxidized. And exits as gas or a second layer forms at the bottom of the fluid.

Some phosphorus is also oxidized and destroyed. The remaining phosphorus is separated with the aid of an exit door at the bottom of the pot filled with fluid. And cool it. In this way pure phosphorus is obtained.

Physical Properties:

Ordinary phosphorus or white phosphorus is a soft solid. It can be sliced with a knife. It is colorless or white. But due to the effect of light, its color gradually turns yellow. It smells like garlic. Its melting point is 44⁰C and the boiling point is 287⁰C. It is insoluble in water.

And soluble in Benzene, carbon disulfide and turpentine oil. By 1000⁰C it has an atom of form P₄. But at higher temperatures than it has Molecular Form P₂. White phosphorus is a highly toxic substance. It is also fatal in low volume (0.15gm). When in contact with its vapor, it makes the bones strangled.

Phosphorus is a more productive element. It reacts with many substances only at ordinary temperatures.

Sodium

3Na + P → Na₃P

Calcium

3Ca + 2P → Ca₃P₂

Sulphur

3S + 2P → P₂S₃

Chlorine

2P + 3Cl₂ → 2PCl₃

2P + 5Cl₂ → 2PCl₅

Oxygen

4P + 3O₂ → 2P₂O₃

4P + 5O₂ → 2P₂O₅

When phosphorus is left open in the air, it reacts with oxygen of the air to form P₂O₃ and P₂O₅. Initially, this process of oxidation of phosphorus is slow. In this activity, heat is generated and temperature increases. After some time, when the temperature exceeds 30⁰C, phosphorus starts burning. For this reason, do not keep it open in the air. But they keep it in water.

Energy is produced in its action with oxygen. And some part of the energy is released as green-yellow light. It glows when the inner phosphorus is kept open in the dark. This property of phosphorus is called phosphorescence.

Reaction with Acid:

It is oxidized to phosphoric acid when heated with concentrated sulfuric or nitric acid.

2P + 5H₂SO₄ → 2H₃PO₄ + 5SO₂ + 2H₂O

P + 5HNO₃ → H₃PO₄ + 5NO₂ + H₂O

Alkali action:

This phosphine gas is formed when heated with a concentrated solution of alkalis.

4P + 3KOH + 3H₂O → 3KH₂PO₂ + PH₃↑

4P + 3NaOH + 3H₂O → 3NaH₂PO₂ + PH₃↑

Reducing properties:

It reduces the salts of copper, gold etc.

It reduces the copper sulfate in cold solution to copper and in hot solution to copper phosphide.

5CuSO₄ + 2P + 8H₂O → 5Cu + 2H₃PO₄ + 5H₂SO₄

3CuSO₄ + 4P + 6H₂O → Cu₃P₂ + 2H₃PO₃ + 3H₂SO₄

Structure of White Phosphorus:

A molecule of white phosphorus has four atoms. Each atom is sp³ hybridized and forms three single bonds with the other three phosphorus atoms. Thus a single electron pair is left on each phosphorus atom.

The structure of the white phosphorus molecule is tetrahedral. A phosphorus atom is located on the four vertices of the tetrahedron.

According to sp³ hybridization in the phosphorus molecule, the p -p -p bond angle should be around 109⁰ 28’ while the bond angle is actually 60⁰. Due to this the phosphorus molecule is strained. Due to this deformation, phosphorus is very active and reacts with many elements at ordinary temperatures.

Allotropy of Phosphorus

Phosphorus exhibits allotropy. White phosphorus is the major among them. Generally, white phosphorus is called phosphorus. The following is a brief description of other forms of phosphorus.

Red Phosphorus:

Red phosphorus is obtained by heating white phosphorus in the presence of iodine or any inert gas at about 280⁰C.

White phosphorus + I₂ or other inert gas -240⁰C→ Red Phosphorus + 4.22Kcal

For the industrial manufacture of red phosphorus, the white phosphorus is mixed with a small amount of iodine and heated to about 280⁰C.

Thus, the majority of white phosphorus is converted to red phosphorus by heating. The mixture obtained is heated with a NaOH solution to separate red phosphorus from white phosphorus.

White phosphorus dissolves in NaOH as it is more reactive. And red phosphorus remains indestructible. After filtering this solution, wash the residue with water and dry it and get red phosphorus in a pure condition.

Sinduri Phosphorus

When white phosphorus is heated for 10 hours with a phosphorus tribromide solution, Sinduri phosphorus is obtained. It burns rapidly in the air like white phosphorus. In other properties, it is similar to red phosphorus.

α-Black Phosphorus

When red phosphorus is heated to 530⁰C in a closed drain, α-black phosphorus is obtained. It is not oxidized by oxygen of air at ordinary temperature.

β-Black Phosphorus

When white phosphorus is heated to 200 temperature and very high pressure, it turns into β-black phosphorus. It does not burn up to 400 in the air. Its structure is similar to that of graphite and it is the conductor of electricity.

Phosphorus Uses

Following are the major uses of phosphorus

Red phosphorus is used in making matches.

Phosphorus is used to make a useful Egyptian metal called Phosphor bronze. The Phosphor bronze consists of copper, tin, and phosphorus.

Phosphorus is used in making explosives, smoke screens, and fireworks.

Phosphorus is used to make some useful chemicals like hypophosphorous acid, phosphorus pentachloride, and Phosphoric Acid. hypophosphorous acid is also used in medicine.