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Sulphur Dioxide


Table of Content

In the colored particle models, sulphur is yellow and oxygen is red.

 Four diverse ways scientists use to demonstrate a particle of sulfur dioxide

Fig. 1: Four diverse ways scientists use to demonstrate a particle of sulfur dioxide

Methods to Prepare Sulphur Dioxide Gas

Sulphur dioxide is set up in the laboratory by the activity of dilute sulphuric acid on sulphites

     Na2SO3        +       H2SO4            → Na2SO4                    + H2O           + SO2
Sodium sulphite         Sulphuric acid      Sodium sulphate      water          Sulphur dioxide

Laboratory preparation of sulfur dioxide

Fig. 2: Laboratory preparation of sulphur dioxide

Commercially, vast volumes of sulphur dioxide are set up by cooking a sulphide ore, for example, iron sulfide. The gas is liquefied subsequent to drying under 25 atm pressure and stored in steel barrels.


Fe2S3  +  4O2         →        FeO +  3SO2

              Liquefaction 25 atm
So2 (g)              →                       SO2(l)

Industrial preparation of sulfur

Fig. 3: Industrial preparation of sulphur

Sulphur dioxide is likewise obtained on an extensive scale by blazing sulphur in air.

S        +    O2      →        SO2

Physical Properties of Sulphur Dioxide

  • Sulphur dioxide is a dull gas with a pungent smell similar to smoldering sulphur.

  • It is one of the most straightforward gasses to melt, since it consolidates at room temperature under a pressure of 2 atm.

Chemical Properties of Sulphur Dioxide

  • It is an acidic oxide that is readily dissolvable in water.

  • It breaks up in water to give sulphurous acid.

       SO2             +       H2O     →     H2SO3
Sulphur dioxide           Water         Sulphurous acid

  • It reacts promptly with sodium hydroxide solution and structures sodium sulphite.

       SO2             +       2NaOH                   →     Na2SO3          + H2O
Sulphur dioxide            Sodium hydroxide         Sodium sulphate          Water

  • In the event that more sulfur dioxide is passed into this arrangement, sodium hydrogen sulphite is framed.

       SO2             +         Na2SO3                   →         H2O     +         2NaHSO3  
Sulphur dioxide            Sodium sulphate                      Water           Sodium hydrogen sulphate  

  • The sulphur particle in a sulphur dioxide atom is tetravalent. Subsequently, it can augment it's covalency to six by specifically consolidating with elements like O2 and Cl2 to shape the comparing addition compounds.

Example: It reacts with chlorine within the presence of charcoal as an impetus to give sulphuryl chloride (SO2Cl2).

         SO2             +           Cl2                →              SO2Cl2
Sulphur dioxide                 Chlorine       (Catalyst)      Sulphuryl Chloride

  • Within the sight of vanadium pentoxide as an impetus, it gives sulphur trioxide.

         2SO2             +           O2                →              SO3
Sulphur dioxide                 Oxygen                           Sulphur trioxide

  • Within the sight of moisture, it can start giving nascent oxygen, and, along these lines, go about as a reducing agent.

Example: It reduces ferric salts to ferrous salts, and halogens to halogen acids.

 2Fe3+  +  SO2     + 2H2O     →   2Fe2+     +  SO42-   +   4H+
Ferric     Sulphur       water           Ferrous
   salt        dioxide                               salt
X2           +   SO2     + 2H2O     →   SO42-     +  2X -   +   4H+
Halogen     Sulphur       water                                   halogen
                     dioxide                                                   acid

Identifying Tests for Sulphur Dioxide Gas

  • It decolorizes acidified KMnO4 solution

    5SO2     + 2KMnO4       + 2H2O  → K2SO4     +      2 MnSO4 + 2H2SO4
Sulphur       potassium                       potassium       Manganese       Sulphuric
dioxide       permanganate                     sulphate            sulphate           acid

  • It turns a filter paper moistened with acidified K2Cr2O7 solution green

    3SO2     +   K2Cr2O7       +    H2SO4          →  K2SO4     +      2Cr2(SO4)3 +     H2O
Sulphur       Potassium            Sulphuric             potassium        chromium      
dioxide           dichromate               acid               sulphate            sulphate      

  • It turns starch iodate paper blue

   5SO2   +    2KIO3   +  4H2O →  2KHSO4     +   3H2SO4     +   I2
Sulphur     potassium     Water      potassium       Sulphuric        Iodine
 dioxide        iodate                       hydrogen            acid

Structure of Sulphur Dioxide

It is angular shaped with an O-S-O bond edge of 119.50. Take note of that despite the fact that sulphur dioxide has two unique sorts of pi bonds, i.e. p pi - p pi and d pi - p pi.

The two sulphur-oxygen bond lengths are equivalent. This shows sulphur dioxide is a resonance hybrid of two canonical structures.

Resonance forms of sulfur dioxide

Fig. 4: Resonance forms of sulphur dioxide

 Bond angle of sulfur dioxide

Fig. 5: Bond angle of sulphur dioxide



The different uses of sulphur dioxide are:

1) In the assembling of sulphites, sulphuric acid,  and hydrogen sulphite.

2) In the sugar business, for refining and decolorizing sugar.

3) For refining lamp oil, and other petroleum items.

4) As a disinfectant.

5) As a fumigant.

6) For dying fragile articles.

7) As antichlor, to expel the overabundance chlorine from substances those have been faded by chlorine.

8) As a glue solvent.

9) As a refrigerant in refrigerators.

10) As an additive for wines, meat, dry natural products and so on.

Summary of the uses of sulfur

Fig. 6: Summary of the uses of sulphur

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Sulphur Dioxide


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