Summary notes for CIE IGCSE Chemistry Topic 12: Sulphur
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Course
Chemistry
Institution
GCSE
Complete revision notes for Topic 12 of the CIE IGCSE Chemistry course: Sulphur. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Sulphur is found in its elemental state underground in the USA, Mexico and Poland.
It is also a by-product from the removal of sulphur from petroleum and natural gas.
Sulphur can also be obtained from sulphide ores.
Uses
The main use of sulphur is in making sulphuric acid which is a very important
chemical used in many industries
It is also used extensively in making rubber tyres more flexible (vulcanising), where
the rubber is heated with sulphur
Describe the manufacture of sulfuric acid by the Contact process, including essential
conditions and reactions
Sulfuric acid is synthesised by the Contact process which use sulphur and oxygen from air
and is done in three distinct stages.
Stage 1
Oxidation of sulphur: S + O2 → SO2
Stage 2
The main stage is the oxidation of sulphur dioxide to sulphur trioxide using a V 2O5 catalyst:
2SO2 + O2 ⇌2SO3
Temperature: 450oC
The reaction is exothermic, so increasing the temperature shifts the position of
equilibrium to the left in the direction of the reactants
Therefore the higher the temperature, the lower the yield of sulphur trioxide
The optimum temperature is a compromise between a higher rate of reaction at a
higher temperature and a lower equilibrium yield at a higher temperature
Pressure: 2 atmospheres
An increase in pressure shifts the position of equilibrium to the right in the direction
of a smaller number of gaseous molecules
However the position of equilibrium lies far to the right (the equilibrium mixture
contains about 96% sulphur trioxide)
So the reaction is carried out at just above atmospheric pressure because:
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