Category Chemistry

               Gold is unusual because it is found in its metallic form, rather than as a chemical compound. Metallic gold, which is easy to identify and shape, has been mined for thousands of years. Most gold is found in what are called alluvial deposits. They consist of river mud containing tiny particles of gold washed out of rock over thousands of years. Water currents are used to wash away the mud and gravel, leaving the heavy gold particles. Gold is mined in many parts of the world, but most modern gold supplies come from countries such as South Africa and Russia.

               Gold does not tarnish, and this makes it very valuable.lt is used mainly for the manufacture of jewellery and for coating electrical contacts. It is also a very good conductor of electricity.

               The earliest form of mining involved following seams of metal in tunnels driven into the rock. This method is still used today, usually in deep mines where other techniques would be impracticable. Tunnels are dug with explosives and with automatic machines. Some of these mines go thousands of metres into the rock, becoming very hot and dangerous.

               Placer mining uses huge floating dredgers to extract metals such as tin and copper from submerged mud. It extracts large amounts of metal inexpensively, but causes enormous environmental damage. Strip mining is used to obtain coal and minerals that lie close to the surface. Open pit mining involves blasting into the rock to produce a huge quarry from which material is removed, layer by layer.

Picture credit: google

               Mining has taken place since the Stone Age, when flints were mined for making stone tools. By 3500BC, people were mining for copper, which they soon combined with tin to harden it and make tools and weapons. Today we mine minerals, diamonds, metals, coal and rock for building material, using a variety of techniques.

Picture credit: google

               Explosives are substances that release a very large amount of energy in a short time when they burn. They all contain a fuel plus an oxidizer, which is a substance containing sufficient oxygen to burn the fuel. Explosives do not need air to explode, because they contain their own oxygen, and so they can burn in confined spaces or even underwater. Some explosives, such as those in a cartridge detonator, explode violently when hit or heated. Others only cause a violent explosion when confined in a gun barrel or a hole drilled in rock for blasting.

               Gunpowder, the first ever explosive, was invented in China over 1,000 years ago. Large amounts of modern explosives are commonly used in quarrying and mining, as well as for munitions.

Picture credit: google

               Plastics are synthetic materials that consist of long chains of molecules called polymers. When the chains are positioned in long rows the plastic is rigid. When the polymer molecules are tangled together, the plastic is soft and flexible. All plastics can be moulded under pressure into complicated shapes. Thermoplastics melt when they are heated, and this means that they can be remelted at any time. There are other forms of plastic known as thermosetting plastics, which cannot be remelted.

               The majority of plastics are made from synthetic resins, which are usually derived from oil. Other types come from sources such as coal or wood. As they do not conduct electricity, most plastics are excellent insulators, so are widely used in electrical wiring. The main disadvantage of plastics is that they are very slow to break down, causing serious environmental problems when discarded.

Picture credit: google

               Natural rubber comes from a kind of tree that originally grew in South America. Its liquid sap, called latex, is drained from the tree by making cuts in the bark.  The latex is collected and processed into rubber. Natural rubber is very soft and is used for making the soles of shoes and sandals.

               In 1839 Charles Goodyear, an American inventor, found that heating rubber together with sulphur made it much harder. This process, known as vulcanization, made it possible to use rubber for vehicle tyres. Rubber is now used for electrical insulation, motor tyres, cushions, golf balls and many other applications.

               Since World War II most of the rubber we use has been produced synthetically. Rubber’s properties are based on the way its molecules link up into long chains, making giant molecules called polymers.

Picture credit: google