Chemistry 5.5

• Crude oil


  Mixture of hydrocarbons formed from the remains of simple marine organisms (plankton) over millions of years
• Hydrocarbons


  Compounds containing only carbon and hydrogen atoms
• Fractional distillation


  1. Crude oil is evaporated and vapours condense at different temperatures

  2. Each fraction contains hydrocarbon molecules with similar number of carbon atoms and a similar range of boiling points
• Products of fractional distillation

  • Petroleum/refinery gases
  • Petrol (fuel for cars)
  • Naphtha (makes chemicals)
  • Kerosene (fuel for aircraft)
  • Diesel fuel (some cars)
  • Lubricating oil (reduces friction in machinery)
  • Fuel oil (fuel for ships and power stations)
  • Bitumen (for roads and roofs)
• Boiling points


  Those at the bottom of the fractional distillation column have higher boiling points compared to those at the top
• Viscosity


  Those at the bottom of the fractional distillation column are more viscous (sticky) compared to those at the top
• Colour


  Those at the bottom of the fractional distillation column are black, the middle ranges from brown to yellow, and those at the top are colourless
• Flammability


  Those at the bottom of the fractional distillation column are less likely to ignite compared to those at the top
• Chain length


  Those at the bottom of the fractional distillation column have longer chain lengths compared to the top
• Combustion


  Reaction of a fuel with oxygen to release useful energy, mostly as heat but also some light energy
• About 21% of air is oxygen
• Complete combustion


  Fuel reacts fully with a plentiful supply of oxygen
• Combustion of hydrocarbons


  Hydrocarbon + oxygen → carbon dioxide + water
• Test for water


  Observe for condensation
• Test for carbon dioxide

  Use limewater, turns cloudy if present
• Combustion reactions


  • methane + oxygen → carbon dioxide + water

  petrol + oxygen → carbon dioxide + water
• Incomplete combustion


  Limited supply of oxygen, produces carbon monoxide (poisonous)
• Hydrogen as a fuel

  Hydrogen + oxygen → water, produces no greenhouse gases
• Hydrogen is explosive and flammable, hard to store as a liquid</b>
• Fire triangle


  Fire needs oxygen, heat and fuel to ignite
• Methods to extinguish fires


  • Removing oxygen (carbon dioxide extinguishers, fire blankets)
  • Removing heat (water for paper/wood fires, not for electrical/oil fires)
  • Removing fuel (using fire-resistant materials)
• Alkanes


  Saturated hydrocarbons with only single bonds
• Alkenes


  Unsaturated hydrocarbons with a carbon-carbon double bond
• Isomerism


  Two or more compounds with the same molecular formula but different structural formulae
• Catalytic cracking


  Breaks down large hydrocarbon molecules into smaller, more useful molecules by heating to 600-700°C and passing over a catalyst
• The products of cracking must add up to the same number of carbon and hydrogen atoms as the reactants</b>
• Polymers


  Long chains formed by joining many small unsaturated hydrocarbon molecules (monomers)
• Most polymers are unreactive and non-biodegradable, causing environmental issues in landfill
• Recycling plastics


  Reduces plastic waste, uses less energy and crude oil than making new plastics, and lowers greenhouse gas emissions