Allotropes of Sulphur
1. Rhombic or Quadrahederal Sulphur
It is the most stable allotrope of Sulhphur. The element Sulphur exist in nature
in this Rhobic variety. All the other allotrope of sulphur can be converted to
this rhombic sulphur at ordinary room temperature but rhombic sulphur cannot be
converted to other form at room temperature.It is not conductor of heat and
electricity. It is not solube in polar solvent like water and soluble in carbon
disulphite , chloroform etc.It 's melting point is 114.5 C, boiling point is 445 C
and specific gravity is 2.06. It is transparent crystalline having pale yellow colour.
Preparation : When rool of sulphur is treated with carbon disulphite it dissolves, and
the solution thus obtained is transferred in a flat evaporating dish. Carbondisulphite
slowly escapes out as it is a volatile compound leaving behind crystals of sulphur known as
Rhombic sulphur.
2. Monoclinic or Prismatic Sulphur
It is crystalline form of sulphur consisting of S8 atom and the molecule in this type
of sulphur is compactly packed with each other to give needle like crystal lattice.
It has amber colour. It's specific gravity is 1.96, boling point is 440 C and melting point is 119 C. It is bad conductor
of heat and electricity. It is insolube in water and soluble in CS2. It is stable only
above 96 C and slowly converts into rhombic variety at room temperature.
Preparation : It is obtained by melting roll of sulphur and cooling it under a crust
is formed. Few holes are made on the crust and mother luquior is poured from it and
air is passed inside it through the hole. As a result Monoclinic sulphur is obtained.
3. Plastic Sulphur
It is amorphous form of sulphur.When roll of sulphur of sulphur in powder form is
heated abour 160 C in a hard glass TestTube it melts to form dark brown vicsious liquid.\
The hot soultion thus obtained is poured in a cold water in a beaker so that it solidifies
to form dark solid of sulphur havinf elastisity.This is called as plastic sulphur.
It has amber colour. It is non-conductor of heat and electricity. It is insoulbe both
in water and CS2. It's specific gravity is 1.95 and it has no sharp melting point as
it is supercooled solid.Since it is in amorphous form it has no fixed shape but it is
supposed to be remained in long zigzag shape by opening all the 8 atom of sulphur.
4. Milk of Sulphur
When roll of sulphur is treated with Calcium hydrooxide (Ca(OH) 2) it forms Calcium pentaoxide and Calcium thiosulpide and the brown solution thus obtained is filtrated and filtrate solution
is treated with conc Hydrochloric acid to form white colour precipitation of sulphur
know as milk of sulphur.
It is opaque, white solid. It is Insoulbe in water and solube in CS2.At ordinary temperature it also
slowly coverts into Rhombic variety.
0 comments: