- 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.
- Its has various allotropic forms but these can be classified into
- crystalline form (diamond, graphite) and
- amorphous form (cock, Cole , lamp – soot , carbon black , animal charcoal gas carbon, wood charcoal etc. )
- Crystalline forms of carbon
- 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 been prepared.
- It is the hardest natural substance.
- It is insoluble in any solvent.
- It is non – conductor of heat and electricity.
- It burns in air at 900 degree 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 jewelry.
- It is used for cutting hand tools.
- For drawing thin wires , diamond dies are used.
- 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 coals with little iron onside 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 degree 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 refectory 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
- Its common variety is bituminous which is like hard stone and burns with smoky flames.
- The superior quality coal burns without smoke is called anthracite.
- It formed out of carbonization of organic and fossil matter buried deep into the earth, under high pressure and high temperature with very-very limited supplies of air, during centuries.
- Anthracite, bituminous lignite and peat are the types of coal with decreasing c%.
- It used as a fuel.
- It is used in the manufacturing of coal gas.
- The by-product of this process are coak, coal-tar, ammoniac liquor.
- It is a black, thick liquid with unpleasant smell. It is a mixture of about 200 substances.
- Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc.
Interestingly, naphthalene balls used to repel moths and other insects are also obtained from coal tar.
- Coal gas is obtained during the processing of coal to get coke.
- It is used as a fuel in many industries situated near the coal processing plants.
- It is a coal deprived of volatile constituents such as coal gas, ammonia, benzene, phoneme, tar etc.
- It is manufactured from coal by destructive distillation by heating in the absence of air due to which volatile constituent 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 industries.
- When wood is suitably stocked, encased in an earthy/clay cover and ignited with 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 constituent of gun-powder.
- It used for purification of water.
- It is used as a deodorant and decolorizing agent in sugar solution and gas masks.
- When tar or vegetable oil rich in carbon is burnt in an insufficient supply of air, black soot is deposited on the wet blanket 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 eye
- lids decoration.
- 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 disk which is scraped off and packed.
- It is used in the rubber for making automobile tyres.
- It is used as replacement of lamp black used for many a purpose.
Gas carbon and petroleum coke;-
- Gas carbon is produced by scrapping the carbon from the walls of the retort formed as 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 electrode when pressed into sticks , as both are good conductor of electricity
- 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 mobile refrigerant.
- Carbon-14 is a useful radioactive isotope for tracker studies in organic and bio-chemical system , including the determination of the age of material that were once alive.
- The identity and amount of many elements present in trace amount in mixture may be determined by neutron activation anilines.
- The procedure involves the conversion of non-radioactive isotope of chemical elements and determination of the type and intensity of the radioactivity that results.
- Petroleum was formed from organisms living in the sea.
- As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay.
Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas
Refining of Petroleum
- Petroleum is a dark oily liquid.
- It has an unpleasant odour.
- It is a mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.
- The process of separating the various constituents/fractions of petroleum is known as refining.
- Natural gas is a very important fossil fuel because it is easy to transport through pipes.
- Natural gas is stored under high pressure as compressed natural gas (CNG).
- CNG is used for power generation.
- It is now being used as a fuel for transport vehicles because it is less polluting.
- It is a cleaner fuel.
- The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes.
- Such a network of pipelines exists in Vadodara (Gujarat), some parts of Delhi and other places.
- Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilisers.
- India has vast reserves of natural gas. In our country, natural gas has been found in Tripura, Rajasthan, Maharashtra and in the Krishna Godavari delta.