Organic Chemistry

combined science

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  • Organic Chemistry
    • Hydrocarbons
      • Alkanes
        • simplest type of hydrocarbon
        • formula = C2H(2n +2)
        • the alkanes are a homologous series - group of organic compounds that react in a similar way
        • saturated compounds - each carbon atom forms four single covalent bonds
        • first four alkanes:
          • methane: CH4
          • Ethane: C2H6
          • Propane: C3H8
          • Butane: C4H10
      • Hydrocarbon properties change as the chain gets longer
        • the shorter the chain the more runny, volatile (lower boiling point), flammable and less viscous (gloopy) the hydrocarbon is
        • the properties affect how they're used for fuels
      • complete combustion
        • occurs when theres plenty of oxygen
        • hydrocarbon + oxygen = carbon dioxide + water (+energy)
        • during combustion carbon and hydrogen from the hydrocarbon are oxidised
        • hydrocarbons are used as fuel due to the amount of energy released when they completely combust
      • short - chain hydrocarbons are flammable so make good fuels and are in high demand
      • long-chain hydrocarbons are thick, gloopy liquids like tar which aren't useful
    • Fractional Distillation
      • crude oil is made
        • crude oil is a fossil fuel formed by the remains of plants and animals that dies millions of years ago and were buried in mud
        • over millions of years with high temperature and pressure the remains turn into crude oil which can be drilled up from the rocks
      • used to separate hydrocarbon fractions
        • crude oil is a mixture of lots of different hydrocarbons
        • the differnent compounds in crude oil are separated by fractional distillation
      • how it works
        • 1. the oil is heated until most of it has turned into gas. the gasses enter a fractionating column
          • 2. in the column theres a temperature gradient - hot at the bottom and gets cooler as you go up
            • 3. the longer hydrocarbons have high boiling points - they condense back into liquids and drain out of the column early on
              • 4. the shorter hydrocarbons have lower boiling points - they condense and drain out much later on, near the top of the column
                • 5. you end up with crude oil mixture separated out into different fractions - each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms so have similar boiling points
        • diagram*
    • Uses and Cracking of Crude Oil
      • methods of cracking
        • cracking is a thermal decomposition reaction - breaking molecules down by heating them
        • 1. heat long-chain hydrocarbons to vaporise them
          • 2. then the vapour is passed over a hot powdered aluminum oxide catalyst
            • 3. the long-chain molecules split apart on the surface of the specks of catalyst (catalytic cracking)
              • 4. you can crack hydrocarbons if you vaporise them, mix them with steam and then heat them to a very high temperature - steam cracking
      • uses of crude oil
        • oil provides the fuel for most modern transport - diesel oil, kerosene, heavy fuel oil and LGP all come from crude oil
        • the petrochemical industry uses some of the hydrocarbons from crude oil as a feedstock to make new compounds for use in things like polymers, solvents, lubricants and detergents
      • a lot of longer alkane molecules produced from fractional distillation are turned into smaller, more useful ones by the process of cracking
      • as well as alkanes, cracking also produces another type of hydrocarbon, alkenes - more reactive and are used as a starting material when making other compounds/ polymers
    • test for alkenes
      • when orange bromine water is added to an alkane no reaction will happen and the colour will stay the same
      • if bromine water is added to an alkene the bromine reacts with the alkene to make a colourless compound


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