Alkanes

• What is the first step in refining crude oil?

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

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

  The temperature decreases upwards
• What does the separation of fractions depend on?

  Boiling point
• What determines the boiling point of hydrocarbons?

  Size of molecules
• How do van der Waals forces relate to molecular size?

  Larger molecules have larger van der Waals forces
• What happens to similar molecules during distillation?

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

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

  At the bottom at higher temperatures
• What is the nature of the refining process of crude oil?

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

  To distill heavy residues under a vacuum
• How does lowering pressure affect boiling point?

  It lowers the boiling point
• Why is vacuum distillation advantageous?

  It separates heavier fractions without high temperatures
• What is petroleum primarily composed of?

  Alkane hydrocarbons
• What is a petroleum fraction?

  A mixture of hydrocarbons with similar chain length
• What is the boiling point of petrol/gasoline?

  Approximately 20°C
• What is the boiling point of kerosene (jet fuel)?

  Approximately 180°C
• What is the purpose of fractional distillation in the laboratory?

  To separate liquids with similar boiling points
• What is the role of the thermometer in fractional distillation?

  It should be at or below the boiling point
• What happens to vapours with higher boiling points during distillation?

  They condense back into the flask
• What is the function of the condenser in fractional distillation?

  It cools vapours and condenses them to liquid
• What are the economic reasons for cracking hydrocarbons?

  • Shorter C chains are in higher demand
  • Excess larger hydrocarbons are converted to shorter ones
  • Products of cracking are more valuable
• What is cracking in the context of hydrocarbons?

  Conversion of large hydrocarbons to smaller ones
• What type of bonds are broken during cracking?

  1. C bonds
• What is required for the cracking process?

  High temperatures
• What are the conditions for thermal cracking?

  High pressure and high temperature
• What does thermal cracking primarily produce?

  Mostly alkenes
• What is the main advantage of catalytic cracking over thermal cracking?

  It uses lower temperatures and pressures
• What type of hydrocarbons does catalytic cracking produce?

  Branched and cyclic alkanes
• Why are branched and cyclic hydrocarbons preferred in fuels?

  They burn more cleanly and have higher octane numbers
• What is the nature of combustion of alkanes?

  Highly exothermic
• What are the products of complete combustion of alkanes?

  CO2 and H2O
• What occurs during incomplete combustion?

  Produces CO and/or C
• What is a consequence of incomplete combustion?

  Produces toxic carbon monoxide
• What is the environmental impact of soot from incomplete combustion?

  Causes global dimming
• How can SO2 be removed from waste gases?

  By flue gas desulfurisation
• What is the role of calcium oxide in flue gas desulfurisation?

  It reacts with sulfur dioxide
• What is formed when sulfur dioxide reacts with calcium oxide?

  Calcium sulfite
• What is a consequence of SO2 dissolving in atmospheric water?

  It can produce acid rain
• What are the pollutants produced from combustion and their consequences?

  • Nitrogen oxides: toxic, form acid rain
  • Carbon monoxide: toxic
  • Carbon dioxide: contributes to global warming
  • Unburnt hydrocarbons: form smog
  • Soot: causes global dimming and respiratory problems