Sulfur

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Sulfur

This is sulfur.

Symbol S
Atomic number 16
Atomic mass 32.06 amu

Sulfur is of ancient origin. It is a nonmetal which exists in a three different allotropic forms. Sulfur compounds are found in varying amount in all natural petroleum. This is a problem because most sulfur compounds have unpleasant odours, and on combustion produce sulfur dioxide, an atmospheric pollutant.

Forms

  1. Orthorhombic
    • The orthorhombic form is the most common crystalline form because it is the most stable form below 96°C. It is a yellow, brittle solid which occurs in S8 rings. It can be found in Sicily, Mexico, and some southern states of the USA.
  2. Monoclinic
    • Monoclinic sulfur is another crystalline form of sulfur. It has the same type of S8 rings, packed in different ways to form their crystals. Monoclinic sulfur is stable only between 96°C and 119°C. It forms naturally as molten sulfur and gradually cools through that temperature range. Below 90°C, monoclinic sulfur quickly returns to the orthorhombic form.
  3. Amorphous
    • When heated to above 120°C, sulfur becomes a liquid. When heated above 200°C it becomes dark-coloured and viscous. This change is due to the breaking open of the S8 rings to form chains and the atoms at the ends of the chains have electrons that are easily excited by absorption of light and cause the dark colour. The S8 chains join up to form long chains which coil around one another giving the increase in viscosity.

When the dark viscous liquid is quenched in cold water, the coiled molecules do not have time to re-form the S8 molecules and to arrange themselves in orthorhombic crystals. The product is a soft, elastic material and is an example of a super-cooled liquid. It is difficult to maintain in its amorphous form because it gradually reverts to the more stable orthorhombic form.

Usage

Most commercially available sulfur is used in the manufacture of sulfuric acid, H2SO4. This is the primary acid of chemical industry because it is one of the cheapest, and it is used in the manufacture of many other acids. Sulfuric acid is made at many locations across Canada by several companies. The largest Canadian producer is C.I.L. which makes most of its acid at Copper Cliff, Ontario. Sulfur dioxide from the roasting of iron sulfide ore in INCO's iron ore recovery plant is converted to sulfuric acid by the contact process.

Among the major uses of sulfuric acid are:

  • as an electrolyte in automobile batteries,
  • in the manufacture of fertilizers,
  • in the manufacture of sulfate and sulfide compounds,
  • in insecticides,
  • in dyes,
  • in the manufacture of vulcanized rubber,
  • in the processing of paper pulp,
  • in photoengraving, and
  • in etching of metals.

Effect on the environment

Much of the air pollution by sulfur dioxide in Southern Ontario comes from the combustion of coal or oil in Ontario Hydro's fossil fueled generating stations. These fuels contain some sulfur combined in organic compounds.

So2a.gif

A major source of atmospheric SO2 in the Sudbury region is the roasting of sulfide ores during the extraction of copper and nickel at the INCO (Thompson, Manitoba) and Falconbridge (Sudbury, Ontario)smelters. Local problems have been alleviated by the construction of very high stacks which enable the SO2 to be diluted with air before it reaches the ground near the smelters.

This contributes to the problem known as acid rain. SO2 is very poisonous to both animals and plants, and can also lead to asthma attacks.


So2b.gif

See also

Periodic table of the elements