10. Chemistry of the environment
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Where can sulfur be found in its elemental state?
Sulfur is found in its elemental state underground in the USA, Mexico and Poland
How can sulfur be obtained as a by product?
It is also a by-product from the removal of sulfur from petroleum and natural gas
In what ores can sulfur be found?
Sulfur can also be obtained from sulfide ores
What are the main uses of sulfur?
• in making sulphuric acid • in making rubber tires more flexible (vulcanising)
Why is sulphuric acid important?
is a very important chemical used in many industries
What does vulcanising consist of?
the rubber tyre is heated with sulfur to make it more flexible
How can sulfur dioxide be made?
Sulfur dioxide can be made by the direct combination of sulphur with oxygen
What are 2 uses of sulfur dioxide?
As a bleach in the manufacture of wood pulp for paper As a preservative for foods and drinks by killing bacteria
How are sulfites used?
Sulfites are often added to foods and these release sulfur dioxide in acidic conditions
• How can sulphuric acid be made? contact process
Sulfuric acid is synthesised by the Contact process
• What is used in the contact process? contact process
which use sulfur and oxygen from air
• how many stages does the contact process have? contact process
3
• What is the first stage? Give CE contact process
The first stage is the oxidation of sulfur: S + O2 → SO2
• What is the second stage? Give CE contact process
The main stage is the oxidation of sulfur dioxide to sulfur trioxide 2SO2 + O2 ⇌2SO3
• What catalyst is used in the second stage? contact process
uses a V2O5 catalyst
• In which stage do the conditions need to be considered? contact process
The conditions for the main stage of production of sulfur trioxide need to be considered
• What temperature and pressure need to be kept in stage 2? contact process
Temperature - 450 degrees C Pressure - 2 atm
• Why, in terms of equilibrium, is the temperature 450ºC? contact process
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 sulfur trioxide
• What is 450ºC a compromise between? contact process
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
• Why, in terms of equilibrium, is the pressure 2atm? contact process
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% sulfur trioxide)
• Why, in terms of manufacture, is the pressure 2atm? contact process
So the reaction is carried out at just above atmospheric pressure because: a) it is not worth spending the extra energy or money required to produce high pressures b) a higher pressure would increase the problems of dealing with the corrosive mixture of gases
• What is produced during stage 3? Give CE contact process
Once stage 2 is completed, the sulfur trioxide is absorbed into a solution of 98% sulphuric acid to produce a thick liquid called oleum: SO3 + H2SO4 → H2S2O7
• Why is the sulfur trioxide dissolved into sulphuric acid and not, for example, water? contact process
It is not absorbed into water because a fine mist of sulfuric acid would be produced and this would be difficult to condense and is also highly dangerous
• Why is the sulfur trioxide dissolved into sulphuric acid and not, for example, water? contact process
It is not absorbed into water because a fine mist of sulfuric acid would be produced and this would be difficult to condense and is also highly dangerous