Alkanes and Halogenoalkanes

• What is the first step in the process of refining crude oil?


  Oil is pre-heated
• What happens to the fractions during fractional distillation?


  The fractions condense at different heights
• How does the temperature change in the fractional distillation column?

  The temperature of the column decreases upwards
• What does the separation of fractions in fractional distillation depend on?


  The separation depends on boiling point
• What factor influences the boiling point of hydrocarbons?


  Boiling point depends on the size of molecules
• How do van der Waals forces relate to the size of molecules?

  The larger the molecule, the larger the van der Waals forces
• What happens to similar molecules during fractional distillation?


  Similar molecules condense together
• Where do small molecules condense in the fractional distillation column?


  Small molecules condense at the top at lower temperatures
• Where do big molecules condense in the fractional distillation column?


  Big molecules condense at the bottom at higher temperatures
• What is the nature of the process of fractional distillation?


  • It is a physical process
  • Involves the splitting of weak van der Waals forces between molecules
• What is the purpose of a vacuum distillation unit?


  It distills heavy residues from the fractionating column under a vacuum
• How does lowering the pressure affect boiling points in vacuum distillation?


  Lowering the pressure over a liquid will lower its boiling point
• What is the advantage of vacuum distillation?


  It allows heavier fractions to be further separated without high temperatures
• What is petroleum primarily composed of?

  Petroleum is a mixture consisting mainly of alkane hydrocarbons
• What is a petroleum fraction?


  A petroleum fraction is a mixture of hydrocarbons with a similar chain length and boiling point range
• What are some examples of petroleum fractions?

  • Naphtha (chemicals)
  • Fuel oil
  • Bitumen
  • Lubricating oils
  • Diesel oil
  • Kerosene (jet fuel)
  • Fuel gas (bottled)
  • Petrol/gasoline
• What is the boiling point range for petrol/gasoline?


  20°C to 40°C
• What is the boiling point range for kerosene (jet fuel)?


  180°C to 250°C
• What is the boiling point range for diesel oil?


  250°C to 340°C
• What is the boiling point range for fuel oil?


  110°C to 180°C
• What is the boiling point range for bitumen?


  Above 340°C
• What is the process of fractional distillation in the laboratory?


  1. Heat the flask with a Bunsen burner or electric mantle
  2. Vapours of all components are produced
  3. Vapours pass up the fractionating column
  4. Lower boiling point vapour reaches the top first
  5. Thermometer should be at or below the boiling point of the most volatile substance
  6. Higher boiling point vapours condense back into the flask
  7. Only the most volatile vapour passes into the condenser
  8. The condenser cools vapours to liquid for collection
• What is the purpose of fractional distillation?


  It is used to separate liquids with similar boiling points
• Why is cracking economically important?


  Shorter C chains are in more demand than larger fractions
• What is the purpose of cracking in petroleum processing?


  To make use of excess larger hydrocarbons and supply demand for shorter ones
• What are the products of cracking?


  The products of cracking are more valuable than the starting materials
• What is the definition of cracking?


  Cracking is the conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds
• What type of bonds are broken during cracking?


  Cracking involves the splitting of strong covalent bonds
• What are the conditions for thermal cracking?


  High pressure (7000 kPa) and high temperature (400°C to 900°C)
• What is the main product of thermal cracking?


  Thermal cracking produces mostly alkenes
• What is the reaction equation for thermal cracking of octane?


  C$_8$H$_{18}$ → C$_6$H$_{14}$ + C$_2$H$_{4}$
• What are the conditions for catalytic cracking?


  Slight or moderate pressure and high temperature (450°C) with a zeolite catalyst
• What types of hydrocarbons does catalytic cracking produce?


  Catalytic cracking produces branched and cyclic alkanes and aromatic hydrocarbons
• Why are branched and cyclic hydrocarbons preferred in fuels?


  They burn more cleanly and provide a higher octane number
• What is the nature of combustion of alkanes?


  Alkanes readily burn in the presence of oxygen and the combustion is highly exothermic
• What are the products of complete combustion of alkanes?


  The products are CO$_2$ and H$_2$O
• What is the reaction equation for the complete combustion of octane?


  C$_8$H$_{18}$ + 12.5 O$_2$ → 8CO$_2$ + 9 H$_2$O
• What occurs during incomplete combustion of alkanes?


  Incomplete combustion produces less energy per mole and can produce CO and/or C
• What are the products of incomplete combustion of methane?


  Products can include CO (toxic) and/or C (sooty flame)
• What is the environmental consequence of soot from incomplete combustion?


  Soot can cause global dimming by reflecting the sun’s light