Preparation of Sulphur dioxide:

In the laboratory, Sulphur dioxide is prepared by the reaction of metallic sulphite or metallic bisulphite with dilute acid.

For example:

A reaction between the dilute sulphuric acid and sodium sulphite will result in the formation of SO2.

Na2SO3 +H2SO4        Na2SO4+H2O+SO2

Properties of Sulphur dioxide:

• Physical properties

• Chemical properties

Physical Properties:

• 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 dissolved in water.

• Sulphur dioxide breaks up in water and gives out sulphurous acid.

• SO2 + H2O2 SO3

• 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

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

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

• 2Fe3+ + SO2  + 2H2O   2Fe2+ + 4H+

• X2 + SO2 + 2H2O         SO42- + 2X-+ 4H+

Reactions of Liquid Sulphur Dioxide (SO2):

Different types of reactions can occur in the presence of liquid Sulphur dioxide as medium and sometimes solvent. Some reactions also shows SO2 in a product, they are given below are;

1. Acid-base reactions

2. Redox reactions

3. Solvolysis  reactions

4. Metathetical reactions

5. Solvation reactions

6. Precipitation reaction

7. Complex Formation reaction

1. Acid-Base Reactions:

In liq.SO2, acid-base reaction is that in which a compound containing or making available SO22+ as a byproduct combines with a compound containing or making available SO32- ion to form the salt and the solvent.

1. SOCl2(acid)+ Cs2SO3(base) 2CsCl(salt) + 2SO2(solvent)

Actually the reaction takes place through the following steps:

SOCl2(acid) SO2+ + 2Cl-

Cs2SO3(base) 2Cs + SO2+2

SOCl2+ Cs2SO3 2Cs Cl- + SO2++ SO2+3

2. SO(SCN)2(acid)+ K2SO3(base) 2K(SCN)(salt) + 2SO2(solvent)

In this reaction acid SO(SCN)2 and base K2SO3 react to form salt of K(SCN) and two molecules of Sulphur dioxide as a solvent.

3. SOBr2(acid) + [N(CH3)4]SO3(base)2[N(CH3)4]Br(salt) + 2SO2(solvent)

This is another acid base neutralization reaction taking place in between acid of SOBr2 and base of [N(CH3)4]SO3.

4. SOCl2+ Na2SO3 2NaCl +2SO2

This reaction is acid base. SO2 is an acid in SOCl2 and SO32- is acting as a base in Na2SO3. So when both react with each other in aqueous medium of SO2 it results the formation of two molecules of Sulphur dioxide SO2 and table salt.

5. HCl + NaOH NaCl + H2O

In this reaction HCl is an acid and NaOH is base. These strong acid and base react in the medium SO2 in aqueous condition to form liquid water and salt.

Preparation of Sulphur dioxide: