1. Learning Objectives:
After studying this Power Points Presentation, you will be able to-
Explain sulphur dioxide and oxoacids of
sulphur.

2. Sulphur Dioxide
Sulphur dioxide is a colourless gas, about 2.5 times as heavy as air, with a suffocating smell, faint sweetish odour.
Occurrence: Sulphur dioxide occurs in volcanic gases and thus traces of sulphur dioxide are present in the atmosphere. Other sources of sulphur dioxide is the combustion of the iron pyrites which are contained in coal.
Sulphur dioxide also results from various metallurgical and chemical processes.

3. Preparation of Sulphur Dioxide
Sulphur dioxide is prepared by burning sulphur in oxygen or air.
S + O2 → CO2
Sulphur dioxide is usually made in the laboratory by heating concentrated sulphuric acid with copper turnings.
Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O
Industrially, it is produced as a by-product of the roasting of
sulphide ores.
4FeS2 + 11O2 → 2Fe2O3 + 8SO2

4. Properties of Sulphur Dioxide
Sulphur dioxide is a colourless liquid or pungent gas, which is the product of the combustion of sulphur on air.
Its melting point is deg C, its boiling point is -10 deg C and its relative density is 1.43.
The molecule of SO2 is angular. It is a resonance hybrid
of the two canonical forms:

5. Chemical Properties
Sulphur dioxide, when passed through water, forms a solution of sulphurous acid.
SO2 + H2O H2SO3 (aq)
It reacts readily with sodium hydroxide solution, forming sodium sulphite, which then reacts with more sulphur dioxide to form sodium hydrogen sulphite.
2NaOH + SO2 → Na2SO3 + H2O
Na2SO3 + H2O + SO2 → 2NaHSO3

6. Sulphur dioxide reacts with chlorine in the presence of charcoal (which acts as a catalyst) to give sulphuryl chloride, SO2Cl2. It is oxidised to sulphur trioxide by oxygen in the presence of vanadium(V) oxide catalyst.
SO2 (g) + Cl2 (g) → SO2Cl2
2SO2 (g) + O2 g SO3 (g)
When moist, sulphur dioxide behaves as a reducing agent. For example, it converts iron(III) ions to iron(II) ions and decolourises acidified potassium permanganate(VII) solution; the latter reaction is a convenient test for the gas.

7. Uses
Sulphur dioxide is a reducing agent and is used for bleaching and as a fumigant and food preservative.Large quantities of sulphur dioxide are used in the contact process for the manufacture of sulphuric acid.
Sulphur dioxide is used in bleaching wool or straw, and as a disinfectant.
Liquid sulphur dioxide has been used in purifying petroleum products.

8. Oxoacids of Sulphur
Sulphuric oxoacids is very important industrial chemical. A state manufacturing potency can be judged by the measure of sulphuric acid it produces and consumes. It is need for the construct of hundreds of additional compounds and also in many industrial processes. The bulk of sulphuric acid produce is used in the manufacture of fertilizers.Sulphur forms a number of oxoacids such as H2SO3, H2S2O3, H2S2O4, H2S2O5, H2SO6, H2S2O7, H2SO4. A number of these acids are not fixed and cannot be isolated.