Intro4u2u

Although sulphur is in the same group in the periodic table as oxygen, there are more differences in the chemical characteristics of these elements than there are similarities. Thus, while oxygen always displays a valency of two, sulphur displays valences of four (in sulphur dioxide, SO2), six (in thionyl chloride, socl2) and eight (in sulphur hexafluoride, SF8).

In the elemental state, sulphur exists in polymeric forms.

Sulphur is an essential element for living organisms, and is present in some amino-acids.
Discovery

* Sulphur has been known since the beginning of history, and is described in the Bible.

* Sulphur has been used by the Greeks and Romans as a fumigant and disinfectant.

Occurrence

* Sulphur is widely distributed as the free element and combined in compounds.
* Sulphur is found near volcanoes, where it is formed by the reaction of sulphur dioxide and hydrogen sulphide which are associated with the volcanoes.
* Sulphur also occurs in many metal ores, including
o gelena, PbS,
o zinc blende, ZnS,
o cinnebar, HgS,
o stibnite, Sb2S3,
o copper pyrites, Cu2S.Fe2S3, and
o iron pyrites, Fe2S.
* The important sulphate ores include
o gypsum, CaSO4, and
o heavy spar, BaSO4.

Extraction

* Sulphur is separated from the minerals in its ores by heating, when the liquid sulphur drains from the ore body. Normally, part of the sulphur in the ore is burned and the heat used to melt the remaining sulphur so that it leaches from the hot mass. This extraction procedure called the Gill Process, and it is widely used in Sicily.

* Sulphur is extracted from underground ore bodies in the United States using the Frasch Process, where superheated water is pumped underground to melt the sulphur which is then forces to the surface.

Preparation
Properties
Sulphur occurs in a large number of allotropic forms in the solid state. Several liquid forms are also known.

Rhombic Sulphur
Rhombic Sulphur which is also known as Octahedral Sulphur or alpha-Sulphur, is a yellow crystalline solid, which crystallises from a solution in carbon disulphide. X-ray investigation shows this form to consist of eight sulphur atoms in the molecule in a ring structure.

Monoclinic Sulphur
Monoclinic Sulphur which is also known as Prismatic Sulphur or beta-Sulphur, is a yellow crystalline solid, which is obtained by allowing molten sulphur to solidify, when long prismatic needles form on the walls of the container that can be separated from the still molten liquid by pouring off the latter. X-ray investigation shows this form to consist of eight sulphur atoms in the molecule in a ring structure, but arranged within the crystal in a different manner to that in rhombic sulphur.

Plastic Sulphur
Plastic Sulphur which is also known as gamma-Sulphur, is a tough elastic substance that is formed when molten sulphur is poured into cold water. On standing it slowly crystallises.

Amorphous Sulphur
Amorphous Sulphur is the insoluble white amorphous solid that remains when flowers of sulphur are extracted with carbon disulphide.

Colloidal Sulphur
Colloidal Sulphur which is also known as delta-Sulphur, is a yellow crystalline solid.
Reactions

* Sulphur burns readily in air forming sulphur dioxide.

S    +    O2    ==>    SO2

*

Sulphur reacts with hydrogen gas when the latter is bubbles
through molten sulphur near its boiling point.

S    +    H2    ==>    H2S

* Sulphur dissolves in caustic alkali solutions forming sulphides and thiosulphates.

4 S  +  6 NaOH  ==>  Na2S2O3  +  2 Na2S  +  3 H2O