1. Sulphur and its Compounds
Chapter 42

2. General properties Group VIA (1s22s22p63s23p4) m.p. 113oC, b.p. 445oC
Allotropes:
(1) Rhombic sulphur, S8 (room to 96oC)
(2) Monoclinic sulphur, S8 (stable btn oC)
(3) Plastic sulphur, long polymeric chains.

3. Range of sulphur compounds
Chemical formulae
Oxidation state
S2-, H2S -2 S8
SCl2, S2O32- +2
SO2, SO32-, H2SO3 +4
SO3, SO42-, H2SO4 +6

4. Burning of sulphur
Sulphur burns with a dull blue flame to form sulphur dioxide, trace of misty sulphur trioxide are also formed.
S + O2  SO2

5. Sulphur dioxide A colourless gas with choking smell
An acidic gaseous pollutant
Readily liquefied under pressure
Very soluble in water and reacts to form sulphuric(IV) acid
Can be further oxidized to SO3, which dissolves in water to form sulphuric(VI) acid, H2SO4

6. Oxidizing properties of SO2
2Mg + SO2  2MgO + S
2H2S + SO2  2H2O + 3S
Aqueous SO2  SO32-(aq)
2MnO4- + 5SO H+  2Mn2+ + 5SO H2O
Cr2O SO H+  2Cr3+ + 3SO H2O

7. Oxidizing properties of SO2
Br2+ SO32- + H2O  2Br- + SO H+
Dye + SO32- + H2O  Dye-O + SO H+

8. Sulphuric(VI) Acid Contact Process
S + O2  SO2 (or 4FeS2 + 11O2  2Fe2O3 + 8SO2)
2SO2 + O2  2SO3 (450oC, V2O5 as catalyst)
SO3 + H2SO4  H2S2O7 (then H2S2O7 + H2O  2H2SO4)

9. A flow diagram Catalytic chamber Heat exchanger drySO2+air SO3
Purifier
and
drier
Air
Heat
exchanger
Catalytic
chamber
Absorption
tower
Sulphur
burner
H2SO4 store
water
98% H2SO4
c.H2SO4
oleum
drySO2+air
SO3

10. Chemical properties of H2SO4
Dilute H2SO4, a typical acid
Zn + H2SO4  ZnSO4 + H2
2NaOH + H2SO4  Na2SO4 + H2O
CuO + H2SO4  CuSO4 + H2O
MgCO3 + H2SO4  MgSO4 + H2O + CO2
2NaHCO3 + H2SO4  Na2SO4 + H2O + CO2

11. Chemical properties of H2SO4
Concentrated H2SO4
As an oxidizing agent
Cu + 2H2SO4  CuSO4 + SO2 + 2H2O
C + 2H2SO4  CO2 + 2SO2 + 2H2O
As a dehydrating agent
Reaction with HX
2HBr + H2SO4  Br2 + SO2 + 2H2O
8HI + 2H2SO4  4I2 + H2S + 4H2O

12. Uses of sulphuric(VI) acid
Manufacture of detergents, dyestuffs, polymers, fibres, paints, fertilizers

13. Test for sulphate(VI) ions
Can be tested by adding a solution of BaCl2 acidified with dil. HNO3
Ba2+ + SO42-  BaSO4, a white ppt.
Note:
Ba2+ +CO32-  BaCO3
Ba2+ +SO32-  BaSO3
BaCO3 + 2HNO3  Ba(NO3)2 + H2O + CO2
BaSO3 + 2HNO3  Ba(NO3)2 + H2O + SO2