Sulfur: the essentials
Sulphur (sulfur) is a pale yellow, odourless, brittle solid, which is insoluble in water but soluble in carbon disulphide. Sulphur is essential to life. It is a minor constituent of fats, body fluids, and skeletal minerals.
The spelling of sulphur is "sulfur" in the USA while sulphur is common elsewhere. IUPAC has does not have jurisdiction over language but has decided sulfur is preferred.
Sulphur is found in meteorites, volcanoes, hot springs, and as galena, gypsum, Epsom salts, and barite. It is recovered commercially from "salt domes" along the Gulf Coast of the USA.
Jupiter's moon Io owes its colours to various forms of sulphur. A dark area near the crater Aristarchus on the moon may be a sulphur deposit. Carbon disulphide, hydrogen sulphide, and sulphur dioxide should be handled extremely carefully. Hydrogen sulphide in very small concentrations can be metabolized, but in higher concentrations it can cause death quickly by respiratory paralysis. It is insidious in that it quickly deadens the sense of smell. Sulphur dioxide is a dangerous component in atmospheric air pollution and is one of the factors responsible for acid rain.
Sulfur: historical information
Sulphur was known in ancient times and referred to in Genesis as brimstone. Assyrian texts dated around 700-600 BC refer to it as the "product of the riverside", where deposits could be found. In the 9th century BC, Homer mentioned "pest-averting sulphur". In 424 BC, the tribe of Bootier destroyed a city's walls using a burning mixture of coal, sulphur, and tar.
Around the 12th century, the Chinese, probably, discovered gun powder (a mixture of potassium nitrate, KNO3, carbon, and sulphur).
Sulphur is one of the elements which has an alchemical symbol, shown below (alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold). Alchemists knew that mercury can be fixed with sulphur.
Possibly Antoine Lavoisier should be credited with convincing the scientific community that sulphur is an element (around 1777).
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for sulphur is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Sulfur: physical properties
Sulfur: orbital properties
Isolation: it is not normally necessary to make sulphur in the laboratory as it is so readily available. It is found as the native element in nature and extracted by the Frasch process. This is an interesting process since it means that sulphur can be extracted from underground without mining it. In the Frasch process underground deposits of sulphur are forced to the surface using superheated water and steam (160°C, 16 atmospheres, to melt the sulphur) and compressed air (25 atmospheres). This gives molten sulphur which is allowed to cool in large basins. Purity can reach 99.5%.
The process in energy intensive. Commercial success for this operation depends upon suitable geological conditions as well as access to cheap water and energy.
Hydrogen sulphide, H2S, is an important impurrity in natural gas which must be removed before the gas is used. This is done by an absorption and regeneration process to concentrate the H2S, followed by a catalytic oxidation (Claus process) using porous catalysts such as Al2O3 or Fe2O3.
8H2S + 4O2 → S8 + 8H2O
Over the years the Claus process has been improved and a modified process can yield 98% recovery.
In the laboratory, sulphur can be purified by recrystallisation from solutions in carbon disulphide, CS2. However the resulting crystals are contaminated with solvent, H2S, and SO2. One good way to purify sulphur is to use a quartz heater (700°C) immersed in liquid sulphur. Carbon impurities decompose to form volatile materials of solid carbon, which coat the heater. After a week or so, finishing with a distillation under vacuum, the result is sulphur with a carbon content of about 0.0009%.
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