The p-Block Elements

Sulphur Dioxide

What happens when sulphur and oxygen, which are in the same group of the periodic table, react? They form sulphur dioxide. But how is this possible? How is this compound formed? What are its properties and uses? Do you want to find out? Then keep reading the article further.

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What is Sulphur Dioxide?

Sulphur dioxide is a common gas that has a pungent smell. We will look at the significance and methods of preparation of this gas in this chapter.

Methods of Preparation of Sulphur Dioxide Gas

We can create sulphur dioxide in the laboratory by the action of dilute sulphuric acid on sulphites

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

sulphur dioxide

(Source: YouTube)

Commercially, chemists produce vast volumes of sulphur dioxide by heating a sulphide ore, for example, let’s say iron sulphide. They, then, liquefy this gas subsequent to drying under 25 atm pressure. It is usually stored in steel barrels. The process of roasting involves the following reaction:

Fe2S3  +  4O2      →     FeO +  3SO2

Liquefaction at 25 atm gives takes place as given below:

So2(g)      →       SO2(l)

We can obtain Sulphur dioxide likewise, on an extensive scale by blazing sulphur in the air.

S    +    O2      →      SO2

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Physical Properties of Sulphur Dioxide

  • Sulphur dioxide is a dull gas.
  • It has a very pungent smell. Its odour resembles smoulder sulphur.
  • It is one of the most straightforward gases to melt. This is because it consolidates at room temperature under a pressure of 2 atm.

Chemical Properties of Sulphur Dioxide

  • It is an acidic oxide.
  • It is readily dissolvable in water.
  • Sulphur dioxide breaks up in water and gives out sulphurous acid.

SO2             +       H2O     →     H2SO3
Sulphur dioxide           Water         Sulphurous acid

  • It reacts vigorously with sodium hydroxide solution and forms sodium sulphite.

SO2       +    2NaOH        →     Na2SO3      + H2O

  • In the cases that we pass more sulphur dioxide into this arrangement, we get sodium hydrogen sulphite.

SO2        +      Na2SO3      →      H2O     +     2NaHSO3

  • The sulphur particle in a sulphur dioxide atom is tetravalent. Subsequently, it can improve it’s covalency to six by specifically reacting with elements like O2 and Cl2 to shape the comparing addition compounds. For example, it reacts with chlorine under the influence of charcoal as a catalyst to give sulphuryl chloride (SO2Cl2).

SO2       +       Cl2       →       SO2Cl2

  • Within the sight of vanadium pentoxide(V2O5) as an impetus, it gives sulphur trioxide.

2SO2      +     O2       →         SO3

  • In the presence of moisture, it can start giving nascent oxygen, and, along these lines, go about as a reducing agent. For example, it reduces ferric salts to ferrous salt, and halogens to halogen acids.

2Fe3+    +    SO2     +    2H2O     →   2Fe2+     +    SO42-    +     4H+

X2        +      SO2     +     2H2O     →     SO42-     +     2X –   +   4H+

Identifying Tests for Sulphur Dioxide Gas

How do we test for the presence of sulphur dioxide gas? Well, it’s easy! We can perform some simple steps to identify this gas. We will talk about them below.

1) It decolorizes acidified KMnO4 solution

It reacts with potassium permanganate to give potassium sulphate, manganese sulphate and sulphuric acid.

5SO2     + 2KMnO4       + 2H2O  → K2SO4     +      2 MnSO4 + 2H2SO4

2) It turns a filter paper moistened with acidified K2Cr2O7 solution green

It reacts with potassium dichromate and sulphuric acid to give potassium sulphate and chromium sulphate.

3SO2     +   K2Cr2O7       +    H2SO4          →  K2SO4     +      2Cr2(SO4)3 +     H2O

3) It turns starch iodate paper blue

It reacts with potassium iodate to give potassium hydrogen sulphate and iodine and sulphuric acid.

5SO2   +    2KIO3   +  4H2O →  2KHSO4     +   3H2SO4     +   I2

Structure of Sulphur Dioxide

It has an angular shape with an O-S-O bond edge of 119.50. We must note 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 similar or equivalent. This signifies that sulphur dioxide is a resonance hybrid of two canonical structures.

Solved Example for You

Q: Mention some common uses of sulphur dioxide gas.

Ans: The different uses of sulphur dioxide include:

  • We use it in the assembling of sulphites, sulphuric acid, and hydrogen sulphite.
  • It is a common ingredient in the sugar industry. It finds its use in the refining and decolourising of sugar.
  • We use it to refine lamp oil and other petroleum items.
  • It is a common disinfectant and a popular fumigant.
  • We use it for dying fragile articles.
  • As an antichlor, we use it to expel the overabundance chlorine from substances those have been faded by chlorine.
  • It is a glue solvent.
  • We use it as a refrigerant in refrigerators.
  • It is used as an additive for wines, meat, dry natural products etc.
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