Sulphur Dioxide

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

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

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.

Roasting,

Fe₂S₃  +  4O₂         →        FeO +  3SO₂

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

Fig. 3: Industrial preparation of sulphur

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

                           Δ
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  
  (excess)

• 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 C_l2 to shape the comparing addition compounds.

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

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

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

                                                              V₂O₅
         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⁺     +  SO₄^2-   +   4H⁺
Ferric     Sulphur       water           Ferrous
   salt        dioxide                               salt
X₂           +   SO₂     + 2H₂O     →   SO₄^2-     +  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
                                                     sulphate

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.

Fig. 4: Resonance forms of sulphur dioxide

Fig. 5: Bond angle of sulphur dioxide

Uses:

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.

Fig. 6: Summary of the uses of sulphur

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Sulphur Dioxide