Red Phosphorus

Red phosphorus is one of the allotropes of phosphorus. It is a derivative of the P4 molecule. Its name comes from its deep red colour and powdery texture.

It was discovered by Austrian chemist Anton von Schrotter in 1847.

Anton von Schrotte discovered Red Phosphorus.
Anton von Schrotter (Source)

Chemical Properties of Red Phosphorus

Chemical FormulaP4
Molar Mass30.974 g mol-1
Density2.34 g cm-3
Melting Point586.85℃
Sublimation Point≈416–590℃

This allotrope of phosphorus exists in a polymeric chain consisting of tetrahedrally structured P4 molecules. Breaking off one of the bonds results in a polymer-like structure, as the broken molecules proceed to bond with the neighbouring phosphorus atoms.

Red phosphorus is odourless and has a deep red colour. It is not harmful or poisonous to humans. It is not as chemically reactive as white phosphorus.

It is kinetically most stable of all the allotropes of phosphorus. It does not ignite in the air at temperatures below 240℃.

Red phosphorus does not have the phosphorescence characteristic, unlike the its white allotrope.

Production of Red Phosphorus

There are basically two ways of producing this chemical

1. From white phosphorus

White phosphorus basically undergoes a gradual transformation to produce its red allotrope in the presence of light and energy in the form of heat. This can be achieved by heating white phosphorus to 300℃. This reaction takes place in the absence of air. It can also be formed by exposing white phosphorus to sunlight.

2. From bone-ash or phosphorus-rich rocks

Rocks/bones that are rich in phosphorus are turned into fine ground powder. This powder is treated with sulfuric acid to give phosphoric acid and calcium sulfate. Heating phosphoric acid with charcoal then results in white phosphorus, which upon further heating yields red phosphorus.

Applications of Red phosphorus

  • It is used as a very effective flame retardant.
  • It can also be used as an elemental photocatalyst for forming hydrogen from water.
  • It finds the largest application in making matches.
  • In some cases, it is used in powerful insecticides.
  • It is also used in flares used for emergency signals.
  • This red chemical can be used as a smoke device, upon mixing with magnesium and a binder.
  • It is also used in the production of the drug methamphetamine(which is also commonly known as meth).

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