Sulphur and Compounds


Sulphur exhibits allotropy:

  •  Yellow Rhombic ( – sulphur)
  • Monoclinic sulphur



Rhombic Sulphur 

(i) It is the common form of sulphur and is formed by slowly evaporating the solution of roll sulphur in CS2, when octahedral crystals of sulphur appear. 

(ii) Its specific gravity is 2.06 g cm3. 

(iii) Its melting point is 385.8 K. 

(iv) This is the most stable form of sulphur at room temperature and all other varieties of sulphur change into this form on standing.

 (v) It is insoluble in water but dissolves to some extent in benzene, alcohol and ether. However, it is readily soluble in CS2. 

(vi) It has low thermal and electrical conductivity. 

(vii) Its specific gravity is 2.07 g cm-3. 

(viii) It is bright yellow in colour. 

(ix) Rhombic sulphur exists as S8 molecules. The sulphur atoms are arranged in a puckered ring. 



Monoclinic sulphur  

(i) This form of sulphur is prepared by melting rhombic sulphur in a dish and cooling till a crust is formed. Two holes are made in the crust and the remaining liquid poured out. On removing the crust, colourless needle shaped crystals of B-sulphur are formed. 

(ii) It is dull yellow in colour and like rhombic sulphur, it is also soluble in carbon disulphide. 

(ii) It has specific gravity of 1.98 g cm-3. 

(iv) Its melting point is 393 K. 

(v) Monoclinic sulphur also exists as S8 molecules with puckered ring structures like rhombic sulphur. However, the two forms differ in the symmetry of their crystals. 

(vi) It is stable above 369K and transforms into α-sulphur below this temperature. Conversely, α-sulphur is stable below 369 K and transforms into β-sulphur above this temperature. Thus, at 369 K both the forms are stable and coexist. This temperature is called the transition temperature. 

Thus, both rhombic and monoclinic sulphur have S8 molecules. These Smolecules are packed to give different crystal structure . The S8 ring in both the forms is puckered and has a crown shape.


Sulphur dioxide 

It contains sulphur in + 4 oxidation state.



Sulphur dioxide is formed together with a little (6-8%) sulphur trioxide when sulphur is burnt in air or oxygen.


S(s) + O2(g) → SO2(g) 

Laboratory Preparation of Sulphur Dioxide

In the laboratory 

(1) Sulphur dioxide is prepared by treating a sulphite with dilute sulphuric acid.


Na2SO3(s) + H2SO4(aq) → SO2 (g) + Na2SO4 (aq) + H2

Sodium sulphite

(2) By heating copper turnings with concentrated sulphuric acid.

Cu + 2 H2SO4 → CuSO4 + SO2 + H2O

Industrially, it is produced as a by-product of roasting of sulphide ores such as iron pyrites or zinc blende.


Cu + 2H2SO4 → 2Fe2O3 + 8SO2

Iron pyrites

2ZnS + 3O 2ZnO + 2SO2

The gas is dried, liquefied under pressure and stored in steel cylinders.



Physical Properties of Sulphur Dioxide 

(i) It is a colourless, toxic gas with a pungent and suffocating odour. 

(ii) It is heavier than air. 

(iii) It is readily soluble in water. At 0°C, 1 volume of water can dissolve about 8 volumes of the gas.

 (iv) It can be easily liquefied at room temperature under a pressure of 2 atmosphere. The liquid is colourless, boils at 263 K and freezes at 197.5 K, giving a white snow-like mass. 

(u) Liquid sulphur dioxide is a good solvent for sulphur, phosphorus, iodine, etc.

Uses of Sulphur Dioxide

(1) It is used in the manufacture of important chemicals such as sulphuric acid , sodium hydrogen sulphite, calcium hydrogen sulphite etc. These bisulphites are used for preservatives for jams, pickles, jellies.

(2) It is used for refining of petroleum and sugar.

(3) It is used for bleaching delicate articles such as wool, silk , straw etc.

(4) It is used as a disinfectant and germicides.

(5) It is as an antichlor i.e. Foe removing excess chlorine from bleached articles.

(6) Liquid SO2 is used as a solvent to dissolve a number of organic and inorganic chemicals.

(7) Liquid SO2 is used as a refrigerant because it can be liquified and re-evaporated easily.


Oxoacids of Sulphur                                 


Oxoacids are acids that have oxygen in them. Sulfur is perceived to make an assortment of oxoacids, including H2SO4, H2SO3, and others. Whenever sulfur is composed of oxygen in oxoacids, it takes on a tetrahedral structure. Sulfur oxoacids as a rule have no less than one S=O bond and an S-OH bond. Notwithstanding S=S and S-OH, there exist terminal peroxide gatherings, terminal S=S, terminal and crossing over oxygen molecules, and chains of (- S-) n.

Sulfurous acid (H2SO3)

Sulphuric corrosive is a diprotic corrosive, meaning it ionizes two photons simultaneously. One sulfur particle is associated with two hydroxyl bunches in sulfurous corrosive, and one oxygen iota shapes a pie association with the sulfur molecule. Sulfur dioxide is broken down in the water and makes it.

Peroxodisulphuric acid (H2S2O8)

Sulfur in the oxidation state is available in Peroxodisulphuric corrosive. Thus, it is a strong oxidizer and exceptionally burnable in nature. Marshall’s corrosive is the normal name for it. It has one peroxide bunch, which goes about as a connection between the two Sulfur particles. Other than the peroxide bunch, each Sulfur molecule is coupled to one hydroxyl bunch (S-OH bond) in addition to two oxygen particles (S=O bond).

Pyrosulphuric Acid (H2S2O7)

Oleum is another name for pyrosulphuric acid. It has a molality of 178.13 g/mol. It’s a white, crystalline solid with a melting point of 36°C that’s an anhydride of sulphuric acid. Excess Sulphur trioxide can be made by reacting it with sulphuric acid. It interacts with bases to generate pyrosulphates, which are salts. It’s used in the production of explosives and dyes. It’s also utilized in the refinement of petroleum.


Sulphuric acid                     

By contact process




1.     Preparation:

2.     Exothermic reaction and therefore low temperature and high pressure are favourable.

3.     It is dibasic acid or diprotic acid.

4.     It is a strong dehydrating agent.

5.     It is a moderately strong oxidizing agent.