Periodicity of sulphur
The element sulphur is found in Group VI of the Periodic Table (just as oxygen), Period 3. It has an atomic
number of 16 and mass number of 16; and its electronic configuration/structure is, 32 16 S: 1s 2 2s 2 2p 6 3s 2 3p 4 .
Occurrence and extraction of sulphur
Occurrence: As a free element, sulphur occurs in nature as a yellow element in huge underground deposits,
mainly in USA – Texas and Louisiana; and it often accompanies volcanic eruption.
In combined forms, it occurs in the form of sulphide ores, such as copper pyrite, CuFeS 2 ; iron pyrite, FeS 2 ;
zinc blend, ZnS; copper glance, Cu 2 S; and galena, PbS. It is also present in gypsum, hydrated calcium
tetraoxosulphate (VI); in traces in the atmosphere as hydrogen sulphide – mainly from the combustion of
fossil fuels.
Extraction: The extraction of sulphur is by a process designed by Herman Frasch (1891) so the process is
known as Frasch Process.
A hole is drilled through the soil layers to the sulphur bed
A sulpur pump of three steel pipes is then driven down the hole
Super-heated water is forced through the outermost tube to the sulphur bed to melt the sulphur
(melting point is 115 0 C)
Hot compressed air is then blown down the innermost tube to force the molten sulphur up through
the middle tube
The molten sulphur then solidifies in a large tank
Allotropes of sulphur
Sulphur exists in two allotropic crystalline states, known as Rhombic sulphur and Monoclinic or prismatic
(β) sulphur; and one amorphous state known as plastic sulphur.
Rhombic () sulphur, obtained by dissolving roll sulphur in liquid carbon (IV) sulphide (in fume cupboard),
is stable at 96°C, and melts at 114°C.
Monoclinic or prismatic (β) sulphur is prepared by dissolving roll sulphur in methylbenzene (toluene) and
warming the solution in water bath. It crystallizes out on cooling as transparent needle-like monoclinic
sulphur. It is stable above 96°C, and melts at 120°C.
Quick
Test:
96°C
is the
transition temperature of the two crystalline sulphur: Explain.
Plastic sulphur, is a non-crystalline (amorphous) and elastic sulphur obtained by pouring molten roll sulphur
into cold water continuously. It is only slightly soluble in carbon (IV) sulphide.
Physical Properties of sulphur
1. It is a yellow, non-metallic solid; and exhibits allotropy.
2. It sublimes to give flowers of sulphur.
3. It is a non-conductor of heat and electricity.
4. It is insoluble in water, but soluble in carbon (IV) sulphide.
Chemical properties of sulphur
1. Combustion in air: It burns with a blue flame to give sulphur (IV) oxide – a colourless gas with an
irritating smell, which turns moist blue litmus paper red:
S (s) + O 2 (g) → SO 2 (g)
2. Reaction with hydrogen: It reacts with hydrogen to give hydrogen sulphide – a colourless gas with a
characteristic rotten egg smell:
S (s) + H 2 (g) → H 2 S (g)
3. Reaction with carbon: When heated in mixture with carbon, it produces a vapour which condenses to
produce a very poisonous and flammable liquid – carbon (IV) sulphide:
2S (s) + C (s) → CS 2 (g)
4. Reaction with metals: It combines with metals to give anhydrous sulphides:
S (s) + Fe (s) → FeS (s)
5. As a reducing agent: When warmed with concentrated H 2 SO 4 , it reduces the acid to sulphur (IV) oxide,
while it gets oxidized to sulphur (IV) oxide
S (s) + H 2 SO 4 (aq) → 2H 2 O (l) + 3SO 2 (g)
When warmed with concentrated HNO 3 , it is oxidized to tetraoxosulphate (VI) acid:
S (s) + 6HNO 3 (aq) → H 2 SO 4 (aq) + 2H 2 O (l) + 6NO 2 (g)
Uses of sulphur
1. It is used in the manufacture of tetraoxosulphate (VI) acid.
2. In the vulcanization of rubber.
3. In the manufacture of carbon (IV) sulphide, gun powder, matches and dyes.
4. In the production of drugs, fungicides, germicides, insecticides and ointments.
5. In the manufacture of calcium hydrogentrioxosulphate (IV), Ca(HSO 3 ) 2 – used in the bleaching of wood-
pulp, for making newsprints.
Hydrogen Sulphide and Oxides of Sulphur
1. Describe the laboratory preparation of hydrogen sulphide.
2. Mention the physical properties of hydrogen sulphide.
3. State the chemical properties of hydrogen sulphide, using equations.
4. Describe how you would test for hydrogen sulphide in the laboratory.
6. Describe how you would test for sulphide ions in the laboratory.
7. Describe the laboratory preparation of sulphur (IV) oxide.
8. State the physical properties of sulphur (IV) oxide.
9. State the chemical properties of sulphur (IV) oxide, using equations.
10. Mention the uses of sulphur (IV) oxide.
Hydrogen sulphide, H 2 S
Hydrogen sulphide is produced naturally the action of bacteria on proteinous substances, such as rotten eggs.
Laboratory preparation of hydrogen sulphide
H 2 S is prepared in the laboratory by the action of concentrated HCl on ground iron (II) sulphide, as shown in
the diagram below:
FeS (s) + 2HCl (aq) → FeCl 2 (aq) + H 2 S↑
(gray) (colourless) (dirty green) (colourless)
The gas thus obtained is wet; and can be dried using fused CaCl 2 , as shown below: