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Sulfur

Sulfur

 

Sulfur – mined from solid underground deposits of elemental sulphur, extracted from fossil fuels, received from metal sulphide ores when the metal is extracted. It is used in the manufacture of sulfuric acid.

 

Sulfur Dioxide – is prepared from when sulphur burns in air or oxygen (burns with a blue flame):

 

S(s) + O2(g) -> SO2(g)

  • Sulfur dioxide dissolves in water to form sulfurous acid (a weak acid) which can lead to the problem of acid rain

 

H2O(l) + SO2(g) -> H2SO3(aq)

  • Sulfur dioxide can cause bronchiospasm in asthmatics
  • It is used as a bleaching agent when paper is made from wood pulp
  • It is used as a preservative for food by killing
  • Sulphites and hydrogen sulphites are also used as preservatives because they liberate SO2 in solution

 

Sulfuric Acid – a typical acid used in fertilisers, paints, pigments, dyestuffs, chemical manufacture, soaps and detergents and fibres.

Contact Process – the industrial preparation of sulfuric acid. All reactions in it are exothermic.

  1. Sulfur is burned in air:

S(s) + O2(g) -> SO2(g)

  1. The SO2 is reacted with further oxygen over a catalyst bed (vanadium (V) oxide). The vanadium (V) oxide is a catalyst which speeds up the reaction without being used up. It melts at 400 °C, spreading to give a larger area. The yield of SO2 is sufficiently high for this stage to be carried out at atmospheric

V2O5

2 SO2(g) + O2(g) <- -> 2 SO3(g)

  1. The sulfur trioxide is reacted with 98% H2SO4 to form oleum, which then reacts with water to form more sulfuric acid. The SO3 must be reacted with sulfuric acid first and not immediately with water as it is too exothermic/violent to carry out

 

SO3(g) + H2SO4(l) -> H2S2O7(l)

H2S2O7(l) + H2O(l) -> 2 H2SO4(l)