SULPHUR


SULPHUR


Sulphur cover 13. Sulphur (ISBN 1- 869860-84-5)

Contents: Introduction; Properties of sulphur; The origin of sulphur; Crystals of sulphur; Minerals containing sulphur; Reactivity of sulphur; Extracting sulphur; Sulphur dioxide; Sulphur dioxide as a bleaching agent; Sulphur dioxide and the environment; Hydrogen sulphide; Sulphuric acid; Sulphates and sulphites; Copper sulphate; Reactions with copper sulphate; Vulcanising rubber; Sulphur in warfare; Sulphur for life; Key facts about sulphur; The Periodic Table; Understanding equations; Glossary of technical terms; Index



Sulphur

Sulphur is a bright yellow, tasteless solid and a very reactive element. It is found in a wide range of minerals and is one of the products of a volcanic eruption. Perhaps this is why many people of previous centuries associated sulphur (also known as brimstone) with the unpleasant afterlife known as Hell. In the New Testament, Hell is described as a "lake that burns with fire and brimstone".

The pure element sulphur has always been thought to have strange properties. A spinning ball of it was used in one of the world's first demonstrations of static electricity. It was found that when the ball was touched by a hand, the ball began to glow.

The element sulphur is a non-metal and will not dissolve in water. The pure element sulphur has very little smell. The smell you might associate with sulphur ­ bad eggs ­ is actually a compound of sulphur, the gas known as hydrogen sulphide. Sulphur compounds are also responsible for the smell in garlic, mustard, onions and cabbage. A sulphur compound even gives skunks their ferociously powerful and long-lasting smell. Indeed, sulphur is a part of all living tissues. Sulphur is fixed into proteins in plants, and acquired by animals who eat the plant materials.

Despite all of the unfortunate connections, sulphur has long had a beneficial medicinal role. It was used both externally, in the form of ointments for the skin and vapours to fumigate diseased places, or internally as the medicine called brimstone. "Brimstone and treacle" was commonly used in Victorian times, and was made famous in the stories of Charles Dickens. In the modern world, the group of drugs known as sulphonamides are used as antimicrobials, one of the more important groups of medicines available today to cure infections of the digestive system.

Because sulphur occurs in all living things,
it may be concentrated as tissues decay. This is why sulphur is a common (and unwelcome) component of coal, oil and, to a lesser extent, natural gas. By burning these fossil fuels, sulphur forms a range of gases, including sulphur dioxide, which may cause acid rain.

Sulphur dioxide is an important gas. As well as forming acid when dissolved in water, it is a bleaching agent used in many industrial processes.

Properties of sulphur A mustard-yellow solid, chemical symbol S
Melts at 119°C, just a little over the boiling point of water
Has no taste
Has no smell
Soft and can be scratched with a fingernail
Poor conductor of electricity and heat
Density 2 g/ml, about twice that of water
Can be found as native sulphur in crystalline form
A very reactive element that combines with almost all other elements
Insoluble in water
Atomic number 16,
atomic weight about 32

The main use of sulphur in large volumes is to produce sulphuric acid, a major starting material in
the production of many fertilisers.


Demonstration of properties of sulphur

Native, or pure, sulphur is a soft, yellow,
crumbly material. By heating it, many of the
special properties of this element are clearly seen.
P The "buckled" ring structure of a molecule of one form of sulphur, as seen from the side and above.
1 Sulphur is usually found in
a laboratory as a crumbly yellow powder. This is the starting material for the demonstrations on the book page.
2 Sulphur melts at 115°C. Despite this low melting temperature, it takes a long while for all of the sulphur to melt because sulphur is a poor conductor of heat.
3 Molten sulphur is an amber liquid that is quite runny (mobile). The reason for this is that sulphur atoms clump into "buckled" rings, each containing eight atoms. The energy of heating allows the rings to spread apart enough to slide over each other.

To imagine how this works, think of a can of spaghetti-rings. When cold, the contents of the emptied can will stand up in a saucepan (they act as a solid), but when heated, the rings start to slide around.

4 When more heat is applied the sulphur darkens and the liquid becomes stickier (more viscous). When it reaches 187°C, the tube can be turned over and the liquid will not move. The extra heating has ruptured the rings and they have formed into chains that are now entangled. (Compare the entangling to strands of spaghetti that have been stirred vigorously.)
5 Heat even further (to 444°C) and
the sulphur turns black. The liquid becomes mobile again because it has reached its boiling point. The extra heat energy has ruptured the chains and they now lie in short lengths that can easily move about. (Compare this to chopping up the strands of spaghetti.)
6. The liquid can now be poured into cold water. Pick it out of the water and it can be pulled about like plastic.
The "crash-cooling" has taken energy away quickly, causing the sulphur to form enormously long chains. As it is moulded,
it gets back some energy and returns to rings, gradually turning back to a solid.