P-Block Elements and Their Compounds-II: Allotropic Form of Sulphur (For CBSE, ICSE, IAS, NET, NRA 2022)

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Uses of Ozone՚s

  • Water purification: Ozone is a powerful germicide and it can purify a water spray effectively.
  • Air purification: Ozone is also used to purify air in tunnels, wells and crowded subways and cinema halls.
  • Refining oils: If ozone is bubbled through oil, all growing bacteria present in the water content of oil are destroyed.
  • Dry bleach: Ozone is also used to bleach waxes, flour, sugar and starch.
  • In Industry and in the Laboratory: It is widely used in certain organic preparation.

Allotropic Form of Sulphur

Rhombic Sulphur

  • This form of Sulphur is normally encountered and consists of structural units packed together to give crystals.
  • Large Crystals can be obtained by allowing a solution of powdered Sulphur in carbon di Sulphide to evaporate slowly.
  • They are yellow, transparent and have a density of .

Monoclinic Sulphur

  • This form of Sulphur is formed when molten Sulphur is allowed to crystallize above 95.6°C.
  • It also consists of structural units, but these are arranged differently than rhombic sulphur in their crystal lattices.
  • Transition temperature for Monoclinic Sulphur is above 95.6°C, below which rhombic Sulphur is more stable allotropic form.

Rhombic Sulphur Monoclinic Sulphur

Crystals of monoclinic Sulphur are amber-yellow in colour and have a density of .

Amorphous Sulphur

  • This forms of Sulphur which possess no regular crystalline form can be obtained when Sulphur is liberated in chemical reactions.
  • For example, by the action of dilute hydrochloric acid on a solution of sodium this-sulphate:

Plastic Sulphur

  • This form can be obtained by pouring nearly boiling Sulphur into cold water.
  • It has completely random arrangement of chains of Sulphur atoms.
  • On standing, it slowly changes over into rhombic Sulphur, as the chains of Sulphur atoms break and reform the Cyclic unit.

Sulphur Dioxide

Priestley obtained this gas by heating mercury with concentrated sulphuric acid and called it vitriolic acid air.


By the reduction of sulphuric acid: It is prepared in the laboratory by reducing hot concentrated sulphuric acid with copper turnings.

By the action of alias on Sulphide or bisulphites:

By burning Sulphur or Sulphide ores:

It is commercially prepared by heating anhydrite with clay and coke at 1200°C.


  • It is a colorless gas with an odour well known as that of burning of Sulphur.
  • Its critical temperature is157.15°C and critical pressure 77.65 atm.
  • It is easily liquified by compression and liquid is colorless, boils at — 10°C and freezes at – 75 ′ 5°C .
  • Liquid Sulphur dioxide is a good solvent for iodine, Sulphur and phosphorus.
  • It is incombustible does not support combustion in the ordinary sense, but heated potassium, magnesium, tin and iron burn in the gas.

When heated to 1200°C it decomposes to an appreciable extent giving Sulphur trioxide and Sulphur.

It is highly soluble in water forming unstable sulphurous acid.

It combines with certain metallic dioxides yielding metallic sulphates, e. g.

It combines with oxygen and with chlorine.

In presence of moisture, it acts as a fairly strong reducing agent. for example

It also acts as an oxidizing agent. Such as

In presence of moisture it acts as a mild bleaching agent

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