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Chemistry-day-12 carbon-compounds-theory Target ssc cgl 2018

Chemistry-day-12 carbon-compounds-theory Target ssc cgl 2018

Chemistry-day-12 carbon-compounds-theory Target ssc cgl 2018

Carbon and its Compounds

Carbon is a non-metal. It is placed in group 14 in periodic table.

Allotropes

Substance with same chemical properties but different physical properties are called allotropes. Allotropes of carbon are…

  • Diamond
  • Graphite
  • Charcoal

Diamond

  • Purest form of carbon.
  • Hardest natural substance.
  • It forms tetrahedral crystals.
  • Bad conductor of electricity and heat.
  • Chemically inert and on heating above 15000C, becomes graphite.

carbon-compounds-theory
Graphite

  • Soft, greasy and dark greyish coloured cryatalline solid.
  • Good conductor of electricity and heat.
  • It has hexagonal layer structure.
  • Layer structure is held by weak van der waal’s force.
  • Chemically more reactive than diamond.

CHEMICAL PROPERTIES OF CARBON COMPOUNDS

Combustion

Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of

heat and light. Most carbon compounds also release a large amount of heat and light on burning. These are the oxidation reactions. Saturated hydrocarbons will generally give a clean flame while unsaturated carbon compounds will give a yellow flame with lots of black smoke.

The gas/kerosene stove used at home has inlets for air so that a sufficiently oxygen-rich mixture is burnt to give a clean blue flame. If you observe the bottoms of cooking vessels getting blackened, it means that the air holes are blocked and fuel is getting wasted. Fuels such as coal and petroleum have some amount of nitrogen and sulphur in them. Their combustion results in the formation of oxides of sulphur and nitrogen which are major pollutants in the environment.

 

Why do substances burn with or without a flame?

You have seen that a candle or the LPG in the gas stove burns with a flame. However, you will observe the coal or charcoal in an ‘angithi’ sometimes just glows red and gives out heat without a flame. This is because a flame is only produced when gaseous substances burn. When wood or charcoal is ignited, the volatile substances present vapourise and burn with a flame in the beginning. A luminous flame is seen when the atoms of the gaseous substance are heated and start to glow. The colour produced by each element is a characteristic property of that element. Try and heat a copper wire in the flame of a gas stove and observe its colour.

You have seen that incomplete combustion gives soot which is carbon.

Formation of coal and petroleum

Coal and petroleum are formed  from biomass which has been subjected to various biological and geological processes. Coal is the remains of trees, ferns, and other plants that lived millions of years ago. These were crushed into the earth, perhaps by earthquakes or volcanic eruptions. They were pressed down by layers of earth and rock. They slowly decayed into coal. Oil and gas are the remains of millions of tiny plants and animals that lived in the sea. When they died, their bodies sank to the sea bed and were covered by silt. Bacteria attacked the dead remains, turning them into oil and gas under the high pressures they were being subjected to. Meanwhile, the silt was slowly compressed into rock. The oil and gas seeped into the porous parts of the rock, and got trapped like water in a sponge.

Hydrogenation of vegetable oils

Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected. This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains. You must have seen advertisements stating that some vegetable oils are ‘healthy’. Animal fats generally contain saturated fatty acids which are said to be harmful for health. Oils containing unsaturated fatty acids should be chosen for cooking. 

What you have learnt

  • Carbon is a versatile element that forms the basis for all living organisms and many of the things we use.
  • This large variety of compounds is formed by carbon because of its tetravalency and the property of catenation that it exhibits.
  • Covalent bonds are formed by the sharing of electrons between two atoms so that both can achieve a completely filled outermost shell.
  • Carbon forms covalent bonds with itself and other elements such as hydrogen, oxygen, sulphur, nitrogen and chlorine.
  • Carbon also forms compounds containing double and triple bonds between carbon atoms. These carbon chains may be in the form of straight chains, branched chains or rings.
  • The ability of carbon to form chains gives rise to a homologous series of compounds in which the same functional group is attached to carbon chains of different lengths.
  • The functional groups such as alcohols, aldehydes, ketones and carboxylic acids bestow characteristic properties to the carbon compounds that contain them.

carbon-compounds-theory
 

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