Crude oil, alkanes and cracking.

• From where is crude oil obtained?

  It is a finite resource found in rock.
• How is crude oil and natural gas made?

  The remains of plankton buried in mud that was heated under high pressure for millions of years.
• What is crude oil?

  A mixture of hydrocarbons.
• What are hydrocarbons?

  Molecules made of hydrogen and carbon atoms only.
• What are alkanes? 


  A type of hydrocarbon with the general formula CnH2n+2.
• What is an homologous series?

  A group of organic molecules with the same functional group where each successive member differs by CH2.
• What is a functional group? 


  An atom or group of atoms on an organic molecule that gives it characteristic chemical reactions.
• Name the first four alkanes.

  Methane, ethane, propane and butane.
• Give the molecular formula of propane.

  C3H8.
• What is fractional distillation? 


  A process used to separate mixtures of substances with different boiling points.
• What is a fraction?

  Fractions are mixtures of hydrocarbons with similar numbers of carbon atoms.
• What can fractions be processed into?

  Fuel and feedstock for the petrochemical industry
• Name five fuels we obtain from crude oil

  Petrol, diesel, kerosene, heavy fuel oil and liquefied petroleum gases
• What products are obtained from the petrochemical industry?

  Solvents, lubricants, polymers and detergents
• Name three properties of hydrocarbons that depend on their size.

  Boiling point, viscosity and flammability.
• How does molecular size affect hydrocarbon boiling point?

  The bigger the molecule, the higher the boiling point.
• How does molecular size affect hydrocarbon viscosity?

  The bigger the molecule, the more viscous it is.
• How does flammability change with the length of an alkane?

  The bigger the molecule, the less flammable it is.
• What is the main purpose of combustion of hydrocarbons?

  To release energy.
• What happens to the atoms of hydrocarbons during combustion?

  The hydrogen is oxidised to form water and the carbon is oxidised to form carbon dioxide.
• What gas in the air is required for combustion?

  Oxygen.
• Write a general word equation for combustion.

  Hydrocarbon + oxygen --> carbon dioxide + water
• Write a balanced symbol equation for combustion of propane.

  C3H8 + 5O2 --> 3CO2 + 4H2O
• What are alkenes?

  A type of hydrocarbon with the general formula CnH2n and there is a C=C double bond.
• Name the first four alkenes.

  Ethene, propene, butene and pentene.
• Give the molecular formula of butene.

  C4H8.
• What is meant by 'unsaturation'?

  Hydrocarbons containing at least one C=C double bond.
• Describe the test for unsaturation.

  Add bromine water.
• Describe the observation for unsaturation.

  Decolourises from orange to colourless
• What is 'cracking'?

  Breaking down hydrocarbons into smaller, more useful alkanes and alkenes.
• Give a general word equation for cracking.

  Alkane --> Alkane + Alkene
• How can you work out the missing molecular formulae in a cracking equation?

  The sum of the atoms in the reactants = the sum of the atoms in the products.
• What conditions are required in cracking?

  Vaporise the alkane at very high temperatures and then either react the vapour with steam or pass them over a hot catalyst.
• Why is cracking required in industry?

  So that less useful hydrocarbons in low demand are turned into more useful hydrocarbons in high demand.