Useful Substances from Crude Oil

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  • Created by: Hope
  • Created on: 09-06-13 14:19

Cracking

Fractions that areproduced by the distillation of crude oil can go through a process called cracking, a chemical reaction which produces smaller hydrocarbons, including alkanes and alkenes. Ethene and other alkenes are unsaturated hydrocarbons and can  be used to make polymers.

 

  • Fuels made from oil mixtures containing large hydrocarbon molecules are not efficent: they do not flow easily and are difficult to ignite.
  • Crude oil often contains to many large hydrocarbon molecules and not enough small hydrocarbon molecules to meet demand. This is where cracking comes in.
  • Cracking allows large hydrocarbon molecules to be broken down inot smaller more useful hydrocarbon molecules.
  • Fractions containg large hyrdocrabon molecules are heated to vaporise them. They are then either: Passed over a hot catalyst or, mixed with steam and heated to a very high temperature

These processes break chemical bonds in the molecules, causing thermal decomposition reactions. Cracking produces smaller alkanes and alkenes (another type of hydrocarbon) Some of the smaller hydrocarbons formed by cracking are used as fuels, and the alkanes are used to make polymers in plastic manufacture

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Alkenes

The products of cracking include alekens (for example ethene and propene) The alkenes are a family of hydrocrabons that share the same general formula: CnH2n  The general formula means that the number of hydrogen atoms in an alkene is double the number of carbon atoms. For example thene is C2H4 and propene is C3H6. Alkene molecules can be represented by displayed formulas in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line 

Ethene= (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ethene_chem_struc.gif)     (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ethene_model.gif)

Propene=     (http://www.bbc.co.uk/schools/gcsebitesize/science/images/propene_chem_struc.gif)     (http://www.bbc.co.uk/schools/gcsebitesize/science/images/propene_model.gif)

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Alkenes

The products of cracking include alekens (for example ethene and propene) The alkenes are a family of hydrocrabons that share the same general formula: CnH2n  The general formula means that the number of hydrogen atoms in an alkene is double the number of carbon atoms. For example thene is C2H4 and propene is C3H6. Alkene molecules can be represented by displayed formulas in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line 

Ethene= (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ethene_chem_struc.gif)     (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ethene_model.gif)

Propene=     (http://www.bbc.co.uk/schools/gcsebitesize/science/images/propene_chem_struc.gif)     (http://www.bbc.co.uk/schools/gcsebitesize/science/images/propene_model.gif)

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Alkenes 2

Alkenes are unsaturated hydrocarbons. They contain a double covalent bond, which is shown as two lines between two of the cabron atoms. The presence of this double bond allows alkenes to react in ways that alkanes cannot .

They can react with oxygen in the air, so they could be used as fuels. But they are more useful than that; they can be used to make ethanol and polymers - two crucial products in today's world.

Testing for unsaturation

Bromine water is dilute solution of bromine, normally orange-brown in colour. It becomes colourless when shaken with an alkene, but its colour remains the same when it is shaken with alkanes.

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