Different Forms of Carbon Allotropy
A phenomenon in which an element is found in different forms having different physical properties but similar chemical properties is known as allotropy.
The different forms are called the allotropic or simply allotropes. Phosphorus, sulphur, carbon etc. are elements which occur in different allotropic forms.
It has various allotropic forms but these can be classified into crystalline form ( diamond, graphite ) and amorphous form ( coke, coal, lamp – soot, carbon black, animal charcoal, gas carbon, wood charcoal etc ).
Crystalline forms of Carbon
1. Diamond : Diamond is the purest form of carbon. It is found very deep inside the earth, in South Africa, Congo, Angola.
Of late, synthetic diamonds have also been prepared.
- It is the hardest natural substance.
- It is insoluble in any solvent
- It is of specific gravity 3.5
- It is non – conductor of Heat and Electricity.
- It burns in air at 900°C and gives out CO2.
- It occurs as octahedral crystals
- It is transparent and has refractive index of 2.45.
- It occurs in Free State.
- It is used in making jewellery
- It is used for cutting hand tools
- For drawing thin wires, diamond dies are used.
2. Graphite : Also called as black lead. As compared to diamond, it is widely available in nature in countries like India, Sri Lanka, Canada, Russia etc.
It can also be produced artificially by heating anthracite coal with little iron oxide of silica in electric furnace.
- It is soft.
- Its specific gravity is 2.3.
- It is good conductor of heat and electricity
- It is black in colour
- It is insoluble in ordinary solvents
- It burns in air at 700 – 800°C and gives out CO2.
- It is of hexagonal crystals.
- It is used in writing pencils and lead.
- It is used as a lubricant for high temperature.
- It is used as refractory material for designing crucibles and electrodes for high temperature.
- It is used in electro – typing and manufacturing of gramophone records for making the non – conducting surface as conducting.
Amorphous Forms of Carbon
3. Coal : Its common variety is bituminous which is like hard stone and burns with smoky flame.
The superior quality coal burns without smoke and is called anthracite.
It is formed out of carbonization of organic and fossil matter buried deep into the earth, under high pressure and high temperature with very – very limited supply of air, during centuries. Anthracite, Bituminous, Lignite and Peat are the types of coal with decreasing C%.
- It is used as a fuel.
- It is used in the manufacturing of coal gas. The by – products of this process are coke, coal – tar, ammonical liquor. Coal – tar is a source for making dyes, explosives, chemicals etc.
- It is also used in manufacturing fuel gases like producer gas, water gas and semi – water gas.
- It is used for manufacturing of synthetic petrol by catalytic hydrogenation of coal.
4. Coke : It is a coal deprived of volatile constituents such as coal gas, ammonia, benzene, phenol, tar etc.
It is manufactured from coal by destructive distillation by heating in the absence of air due to which volatile constituents are left back in the coal.
- It is used as a fuel.
- It is used for making graphite and water gas.
- It is used as reducing agent in iron and steel industry.
5. Wood Charcoal : When wood is suitably stocked, encased in an earthy / clay cover and ignited with a very limited supply of air, the volatile products are allowed to escape, and wood charcoal is obtained.
- It is used as a fuel.
- It is used a constituent of gun – powder.
- It is used for purification of water.
- It is used as a deodorant and decolourising agent in sugar solution and gas masks.
6.Bone Black or Animal Charcoal : When bones are subjected to destructive distillation in a retort, the residue obtained is boneblack or animal charcoal.
7.Lampblack : When tar or vegetable oil rich in carbon is burnt in an insufficient supply of air, black soot is deposited on the wet blankets hung in the room.
- It is used in making Indian ink.
- It is used in making printers ink.
- It is also used by ladies for eyelids decoration.
8. Carbon Black : It is obtained by burning natural gas in the presence of limited supply of air and collecting the soot on the underside of a revolving disc which is scrapped off and packed.
- It is used in the rubber for making automobile tyres.
- It is used as a replacement of lamp black used for many a purpose.
9. Gas Carbon and Petroleum Coke : Gas carbon is produced by scrapping the carbon from the walls of the retort formed as a result of destructive distillation of coal.
When distillation of crude petroleum is done in a retort, the petroleum coke is deposited on the walls of the retort.
- It is used for making electrodes when pressed into sticks, as both are good conductors of electricity.
10. Sugar Charcoal : It is the poorest form of carbon.
- It is obtained when sugar is heated strongly out of contact with air.
- It can be liquefied even to room temperature but under high pressure.
Further, it can be converted into a solid state, known as dry ice which is used as a mobile refrigerant.
11. Carbon – 14 : It is a useful radioactive isotope for tracer studies in organic and biochemical system, including the determination of the age of materials that were once alive.
The identity and amount of many elements present in trace amounts in mixtures may be determined by neutron activation analysis.
This procedure involves the conversion of non – radioactive isotopes of chemical elements and the determination of the type and intensity of the radioactivity that results.
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