Combined state: occurs as sulphates and sulphides in the Earth’s crust. Sulphide ores such as copper pyrites(CuFeS2) and iron pyrites (FeS2). The sulphate ores include gypsum(CaSO4.2H2O)
Free state: occurs as free element in hot springs and volcanic regions in many parts of the world. This is the major source of sulphur.
Extraction of Sulphur
Sulphur deposits occur very deep down about 200 metres underground.
Sulphur is extracted by a method known as Frasch Process.
Main steps involved in the Frasch Process are:
A hole is drilled about 30cm in diameter with an oil drill from the surface down to the sulphur deposits.
Three concentric pipes are put down the hole.
Superheated water of about 170⁰C is forced through the outermost pipe to melt the underground sulphur.
Hot compressed air is passed simultaneously through the innermost pipe.
The compressed air and steam melts the sulphur and form a frothy mixture with the water.
The compressed air (high pressure air) helps to lift the mixture to the surface. As the molten sulphur is brought up to the surface, it solidifies due to the lower temperature at the surface. And separates from water because sulphur is not soluble in water.
Allotropes of sulphur
Allotropy is the existence of an element in two or more different physical forms in the same physical state.
Different physical forms of an element having the same chemical properties but different physical properties are called allotropes.
Crystalline allotropes of sulphur:
Rhombic sulphur
Monoclinic sulphur
Rhombic sulphur
It is also known as ꭤ-sulphur or octahedral sulphur.
It is a bright yellow crystalline solid with an octahedral shape.
It has a melting point of 114⁰C.
It has a density of 2.08g/cm3.
It is stable allotrope below 96⁰C. Above this temperature, it slowly changes into monoclinic sulphur.
Monoclinic sulphur
It is also known as beta (B-sulphur) or prismatic sulphur.
It has the shape of hexagonal prism.
It has a melting point of 119⁰C.
It has a density of 1.98g/cm3
It is stable above 96⁰C. Below this temperature it gradually changes to rhombic sulphur.
Amorphous allotropes of sulphur
Suphur also exists in non-crystalline (amorphous) forms namely, colloidal, plastic and powdery sulphur.
Plastic sulphur is obtained by heating powdered sulphur until it boils. Then the boiled sulphur is then poured in a thin continuous stream of into a container containing cold water.
This produces a long yellow thread of plastic sulphur. It does not dissolve in carbon disulphide. This suphur is elastic because it is coiled in a zig zag fashion.
Colloidal sulphur – it is a yellow crystalline solid
Powdery sulphur –it can be prepared by saturating distilled water with hydrogen sulphide
Note
Each molecule of sulphur consists of eight sulphur joined by covalent bonds., S8.
PROPERTIES OF SULPHUR
(a)Physical properties of sulphur
It is yellow solid at room temperature.
It is insoluble in water but soluble to non-polar solvents such as carbon disulphide and benzene.
The melting point of sulphur is 119⁰C and boiling point of 444⁰C with a density of 2.08g/cm3.
It is poor conductor of heat and electricity.
Chemical properties
Combustion reaction
Sulphur burns in air/oxygen with a blue flame forming sulphur dioxide.
S(s) + O2(g)→ SO2(g)
Reaction with metals
Sulphur combines with heated metals like iron, copper, magnesium and zinc to form metal sulphides.
Fe + S → FeS
Cu + S → Cu2S
Zn + S → ZnS
Mg + S → MgS
Reactions with acids.
It act as reducing agent when reacts with some concentrated acids.
(a) With concentrated sulphuric acid, sulphur is oxidized to sulphur dioxide and sulphuric acid is reduced to water.
S(s) + 2H2SO4(l) → 2H2O(l) + 3SO2(g)
(b) With Concentrated nitric acid, sulphur is oxised to sulphuric acid and nitric acid reduced to reddish brown gas nitrogen dioxide.
S(s) + 6HNO3 (l)→ H2SO4 (aq)+ 6NO2(g) + 2H2O(l)
(c) There is no chemical reaction with dilute acids and concentrated hydrochloric acid.
Reaction with hydrogen
In its molten state, sulphur reacts with hydrogen gas to produce hydrogen sulphide gas.
H2(g) + S(s) → H2S(g)
Uses of sulphur
It is used in the vulcanization of natural rubber. The process of making natural rubber hard for making tyres is called vulcanization.
It is used in the manufacture of drugs, ointments and fungicides.
It is used in the manufacture of sulphuric acid in the contact process.
It is used in the manufacture of gun powder, matches and fireworks.