Chem

• Crude oil is a mixture of hydrocarbons
• Fractional distillation of crude oil

  1. Heat crude oil until it boils

  2. Vapours pass into fractionating column

  3. Vapours cool and condense at different heights

  4. Larger hydrocarbons condense near bottom

  5. Smaller hydrocarbons condense near top

  6. Gases not condensed collected at top
• Main fractions obtained from crude oil

  • Refinery gases
  • Gasoline
  • Kerosene
  • Diesel
  • Fuel oil
  • Bitumen
• Trend in properties of main fractions

  • Boiling point increases
  • Viscosity increases
  • Colour gets darker
  • Flammability decreases
• A fuel is a substance that, when burned, releases heat energy
• Possible products of complete and incomplete combustion of hydrocarbons with oxygen

  • Carbon dioxide
  • Water
  • Carbon monoxide
  • Carbon
• Carbon monoxide is poisonous


  It reduces the blood's ability to carry oxygen around the body
• In car engines, the high temperature allows nitrogen and oxygen from air to react, forming oxides of nitrogen
• Combustion of impurities in hydrocarbon fuels results in the formation of sulfur dioxide
• Sulfur dioxide and oxides of nitrogen contribute to acid rain
• Catalytic cracking of long-chain alkanes


  1. Converts to shorter alkanes and alkenes

  2. Conditions: 600-700°C, silica or alumina catalyst
• Cracking


  Converts less useful heavier fractions to more useful lighter fractions
• A hydrocarbon is a compound of hydrogen and carbon only
• Empirical formula


  Simplest whole number ratio of atoms in a compound
• Molecular formula


  Actual numbers of each type of atom present in a molecule
• Structural formula


  Shows how atoms in a molecule are joined together
• Displayed formula


  Shows all the bonds in a molecule, each line represents a shared pair of electrons
• Homologous series


  Series of compounds with similar chemical properties, same general formula, each member differs by CH2, same functional group
• Functional group


  Atom or group of atoms that determine the chemical properties of a compound

  
• Alkanes


  Saturated hydrocarbons with general formula CnH2n+2
• Alkenes


  Hydrocarbons with one carbon-carbon double bond, general formula CnH2n
• Isomers


  Molecules with the same molecular formula but different structures
• Alkyl groups


  Side-chains in branched alkanes, have one hydrogen atom less than the corresponding alkane
• Crude oil is a non-renewable resource
• As hydrocarbon molecules get bigger

  Boiling point increases, viscosity increases, colour gets darker, flammability decreases
• Carbon dioxide is a greenhouse gas and increasing amounts may contribute to climate change
• Saturated hydrocarbons


  Contain only single carbon-carbon bonds
• Unsaturated hydrocarbons


  Contain double or triple carbon-carbon bonds
• Substitution reaction of alkanes with halogens


  One atom in the alkane is replaced by a halogen atom, requires UV light
• Bromine water reacts with alkenes


  Produces a colourless 1,2-dibromoalkane, used as a test for alkenes
• Hydration of ethene


  Produces ethanol, conditions: 300°C, 60-70 atm, phosphoric acid catalyst
• Alcohols


  Contain the -OH functional group, general formula CnH2n+1OH

  
• Alcohols are volatile and flammable, use a water bath not a naked flame
• Oxidation of ethanol


  Produces ethanoic acid, can be done by microbes in air or by heating with potassium dichromate and sulfuric acid
• Fermentation of glucose


  Produces ethanol, uses yeast enzymes, 30°C, anaerobic conditions
• Carboxylic acids


  Contain the -COOH functional group
• Reactions of carboxylic acids

  1. Dilute acid reacts slowly with metals, producing hydrogen gas

  2. Reacts with metal carbonates, producing carbon dioxide
• Vinegar is an aqueous solution containing ethanoic acid
• Esters


  Contain the -COO- functional group, formed by reaction of an alcohol and a carboxylic acid
• Condensation polymerisation of dicarboxylic acids and diols


  Produces polyesters and water