Sulphur Chemistry

Sulphur Oxides and Oxy-acid
Sulphur forms several oxides of which sulphur dioxide (SO2) and sulphur trioxide (SO3 ) are important.

Sulphur dioxide:
Preparation: It is formed by burning sulphur in air or roasting metal sulphides in the presence of air

S8 + 8 O2 —> 8 SO2

4FeS2 + 11O2 —> 2Fe2O3 + 8SO2

Properties:

1. As reducing agent

(i) Action on halogens :

SO2 + Cl2 +2H2O —> H2SO4 + 2HCl

(ii) Action on FeCl3 :

2FeCl3 + SO2 + 2H2O —> H2SO4 + 2FeCl2 + 2HCl

2. Reaction with acidified KMnO4 :

2KMnO4 + 5SO2 + 2H2O —> K2SO4 + 2MnSO4 + 2H2SO4

3. Reaction with acidified K2Cr2O7 :

K2Cr2O7 + 3SO2 + H2SO4 —> K2SO4 + Cr2(SO4)3 + H2O

4. Oxidising property

(i) 2H2S + SO2 —> 2H2O + 3S

(ii) SO2 + 2Mg —> 2MgO + S

Sulphur trioxide:
Preparation: (i) By catalytic oxidation of sulphur dioxide

(ii) By dehydration of H2SO4

H2SO4 SO3 + H2O

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