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SULPHUR

Sulphur is a yellow non-metallic element belonging to the group VI of the periodic table. In the free state it is found in volcanic regions. In the combined state it occurs as sulphates and sulphides. It is characterised by the following;

1. Atomic number 16
2. Relative atomic mass 32.06
3. Relative density 2.07 for the rhombic form
4. Melting point 112.8OC
5. Boiling point 444.674OC
6. It is a pale yellow coloured solid. Ordinary sulphur is brittle and crystalline.
7. It is insoluble in water but soluble in organic solvents.
8. It a bad conductor of heat and electricity.

EXTRACTION AND PREPARATION

In order to extract underground sulphur, Frasch process is implied. In this process, three concentric pipes are sunk deep into the ground, where the sulphur source is present. Super heated water (170^OC) is forced down the outer pipe, into the sulphur. The sulphur melts. Now, compressed air is blown through inner pipe. This air forces the sulphur, which is in a liquid form, to the surface. The sulphur is now condensed and the purity of sulphur obtained is 99.5%.

ALLOTROPIC FORMS OF SULPHUR

Sulphur has the property to exist in allotropic forms. Below 95.6^OC it exists as a stable crystal form called as ‘rhombic sulphur’. Above this temperature, the rhombic form is transformed into the triclinic form. Both of these crystalline forms contain sulphur as S₈ molecules.

In the molten state sulphur is a yellow liquid consisting of rings (as in the solid form). At much higher temperatures, about 160^OC, the sulphur atoms form chains and the viscosity of the liquid increases, and the colour if the liquid becomes dark brown. In this form if sulphur is cooled suddenly a reddish brown solid called plastic sulphur is obtained.

If the sulphur at 160^OC is further (200^OC) heated then the viscosity again decreases and at the boiling point it vapourises. The sulphur vapours contain sulphur as S2, S4, S6 and S8 molecules. When these vapours are sublimed, then an allotropic form of sulphur called ‘flowers of sulphur’ is obtained.

USES

1. Sulphur is used as a fungicide for plants.

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