P-Block Element and Their Compound – I: Allotropic Form of Phosphorus (For CBSE, ICSE, IAS, NET, NRA 2022)

Glide to success with Doorsteptutor material for NTSE/Stage-I-State-Level : get questions, notes, tests, video lectures and more- for all subjects of NTSE/Stage-I-State-Level.

Nitric Acid,


In laboratory, Nitric acid can be prepared by heating or with concentrated in a glass retort and condensing the vapours coming out of the retort.

In Industry, it is manufactured by the catalytic oxidation of ammonia which involves following reaction (Outward process) .



  • It is a colorless liquid of density at .
  • Nitric acid is freely miscible with water forming a constant boiling mixture containing of, .


In aqueous solution, nitric acid is a strong acid and dissociates to give hydronium and nitrate ions.

It is neutralized by appropriate alkalis to yield nitrates.

On heating it gives

It is a good oxidizing agent and oxidizes non-metals, metals and organic compounds, for example


In the gaseous state exists as a planar molecule with the structure: (fig)

In the Gaseous State


  • It is used as an oxidizing agent in laboratory, e. g. Fe (II) gets oxidized to Fe (III) .
  • Conc. is a constituent of aqua regia .
  • is a constituent of rocket propellant.

Allotropic Form of Phosphorus

  • There are three allotropic forms known as white, red and black phosphorus.
  • White phosphorus is formed as a soft, waxy solid whenever phosphorus vapour is condensed; structurally it contains tetrahedral units held together by van der Waals՚ forces.
  • White phosphorus very slowly changes into the red allotropic form by heating in the absence of air to 270°C for several days.
  • Black phosphorus obtained by subjecting white phosphorus to high pressures at 200°C in the absence of air.
  • White and red phosphorus normally encountered in the laboratory.

Phosphorus Halides

Phosphorus Trichloride,

  • The trichloride, is obtained by passing chlorine over white phosphorus.
  • It is attacked by air and water necessary to displace the air from the apparatus with a stream of carbon dioxide and to include a soda-lime drying tube.

Phosphorus trichloride is readily hydrolyzed by water to phosphonic acid, and hydrogen chloride.

It readily combines with oxygen and chlorine (reversibly) , the phosphorus atom increasing its covalency from three to five:

Phosphorous Pentachloride,

  • Phosphorus pentachloride is prepared by passing chlorine through a flask into which phosphorus trichloride is dripping.
  • This experimented is conducted in an ice-cooled apparatus because it dissociates into the trichloride and chlorine under normal condition.

It is attacked by compounds containing the hydroxyl group. e. g.

The Acid of Phosphorus and Its Properties

The Acid of Phosphorus and Its Properties

Structure of Oxyacid՚s of Phosphorus

Structure of Oxyacid՚s of Phosphorus

Developed by: