Organic chemistry

• Crude oil 


  Non-renewable finite resource
• Crude oil is formed from the fossilised remains of ancient plankton
• Crude oil is found in rocks and is used to produce fuels and other important chemicals
• Crude oil is a mixture of lots of different compounds that are not chemically combined

  Most of the compounds in crude oil are hydrocarbons
• Hydrocarbons are molecules made up of only hydrogen and carbon atoms

  Hydrocarbons differ in size, which can change the properties of the hydrocarbon
• Heavy fractions of crude oil don't make good fuels because they:

  Don't ignite easily

  Have high boiling points

  Have low volatility
• Most compounds in crude oil are hydrocarbons and most of these molecules are alkanes
• Alkanes have general formula Cn H2n+2
• The first four members of an alkane series are methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10)
• Alkane structure 


  In alkanes carbon atoms bond to four other atoms (either hydrogen or carbon)

  These are called saturated hydrocarbons as they only contain single bonds with other atoms
• Alkane uses 


  Alkane are quite unreactive but can burn well

  This makes them useful fuels
• Properties of hydrocarbons 


  Boiling point - Hydrocarbons with longer chains have higher boiling points

  Viscosity - Hydrocarbons with longer chains have higher viscosity (Thicker and flow less easily)

  Flammability - Hydrocarbons with longer chains are less flammable
• Burning hydrocarbons with plenty of oxygen 


  The combustion of hydrocarbons when there is a good air supply involves

  • Energy release
  • The oxidation of carbon and hydrogen to create carbon dioxide and water
• Burning hydrocarbons with a lack of oxygen

  If alkanes are burned then carbon monoxide can be created

  2C + 0₂ -> 2CO

  Carbon monoxide is a colourless, odourless, toxic gas
• Fractional distillation is the process of separating crude oil into groups of hydrocarbons with similar numbers of carbon atoms. We call these groups of hydrocarbons "fractions"
• Long chain hydrocarbons 


  Hydrocarbons with lots of atoms are called 'long-chain hydrocarbons'
• short chain hydrocarbons


  Hydrocarbons with few carbon atoms are called 'short-chain hydrocarbons'
• Fractional distillation stages

  1. evaporation
  2. Condensation
  3. Collection
• Evapouration 


  Crud oil is heated until it evaporates

  Vapour is put into a fractioning column at the bottom and rises upwards
• Condensation 


  The temperature is highest at the bottom of the column. Long-chain hydrocarbons condense at the bottom and are collected as liquids

  Short-chain hydrocarbons have lower boiling points. They pass up the column and condense at lower temperatures nearer the top
• Collection 


  The fractions are collected. They are then processed to create end products:

  Fuels (e.g petrol, diesel) are a common end product

  The petrochemical industry can use some fractions as feedstock (material used in an industrial process) to make solvents, lubricants, detergents etc
• Homologous series 


  There are many different organic (carbon-containing) compounds because carbon atoms can for families of similar compounds. These are now as homologous series
• Cracking 


  The process that breaks down long-chain hydrocarbons into shorter-chain more useful molecules. it is an example of a thermal decomposition reaction
• Catalytic cracking 


  Vapourised heavy hydrocarbons are passed over a hot catalyst

  The products include alkanes and alkenes
• Steam cracking


  Vapourised heavy hydrocarbons are mixed with steam in a high-temperature environment

  The products include alkanes and alkenes
• Uses of alkenes 


  Starting materials for chemicals like ethanol

  Being combined to make polymers