Allotropes and extraction of sulphur

Introduction to Sulphur

Sulphur is a yellow non-metal found in Group 16 of the periodic table. In Nigeria, we mostly see sulphur as a yellow powder used in some medicines or for vulcanizing rubber. It can exist in different physical forms even though it is the same element.

Allotropy is simply when one element can live in different forms in the same physical state.

It means an element has the same chemical properties but different physical appearances.

Allotropes of Sulphur

Sulphur has two main solid forms: Rhombic sulphur and Monoclinic sulphur. There is also a liquid form called Plastic sulphur.

Rhombic sulphur (Alpha sulphur): This is the most stable form at room temperature. It looks like bright yellow crystals shaped like octahedrons.

Monoclinic sulphur (Beta sulphur): This form is stable only when the temperature is above 96 degrees Celsius. It looks like long, thin needles.

Plastic sulphur: This is formed when you heat sulphur until it boils and then suddenly pour it into cold water. It is stretchy like a gala wrapper but eventually turns back to rhombic sulphur.

Transition Temperature

There is a special temperature where rhombic sulphur changes into monoclinic sulphur. This is called the transition temperature.

For sulphur, this magic number is 96 degrees Celsius.

Extraction of Sulphur by the Frasch Process

Sulphur is found deep underground. We cannot use a shovel to dig it like we dig a borehole, so we use the Frasch Process. This process uses three pipes of different sizes fitted into each other.

1. Superheated water (at 170 degrees Celsius) is pumped down the outermost pipe to melt the sulphur underground.

2. Compressed air is blown down the innermost pipe. This air acts like a pump.

3. The pressure from the air forces the molten sulphur and water mixture to rise to the surface through the middle pipe.

Physical Properties of Sulphur

Sulphur is a yellow solid that does not dissolve in water (it is insoluble). However, if you use a liquid like carbon(IV) sulphide, it will dissolve easily. It does not conduct electricity, just like a plastic spoon.