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 molecule size?

  Larger molecules have larger van der Waals forces
• 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 points?

  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 first step in laboratory fractional distillation?

  Heat the flask with a Bunsen burner
• What happens to vapors in the fractionating column?

  They pass up the column
• What should the thermometer indicate during distillation?

  At or below the boiling point of the most volatile substance
• What happens to vapors with higher boiling points during distillation?

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

  To cool vapors and condense them to liquid
• What is cracking in the context of hydrocarbons?

  Conversion of large hydrocarbons to smaller ones
• What are the economic reasons for cracking hydrocarbons?

  • Shorter C chains are in higher demand
  • To utilize excess larger hydrocarbons
  • Products of cracking are more valuable
• What type of bonds are broken during cracking?

  1. C bonds
• What is the general reaction for cracking large hydrocarbons?

  High Mr alkanes → smaller Mr alkanes + alkenes + hydrogen
• What type of process is cracking?

  A chemical process
• What are the conditions for thermal cracking?

  High pressure and high temperature
• What is produced mainly from thermal cracking?

  Mostly alkenes
• What are the conditions for catalytic cracking?

  Slight pressure and high temperature with a catalyst
• What is the advantage of catalytic cracking over thermal cracking?

  It saves energy with lower temperatures
• Why are branched and cyclic hydrocarbons preferred in fuels?

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

  It is 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 carbon soot?

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

  By flue gas desulfurisation
• What reacts with sulfur dioxide in a scrubber?

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

  Calcium sulfite
• What environmental issue is caused by SO2 dissolving in water?

  It produces acid rain