C7 - Organic Chemistry

• Crude oil is a finite resource found in rocks. Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud.
• Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only.
• Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes is CnH2n+2
• The first four members of the alkanes are methane, ethane, propane and butane.
• Alkanes can be represented as either C2H6 or

  
• The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation. The fractions can be processed to produce fuels and feedstock for the petrochemical industry.
• Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil.
• Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergents.
• The vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds.
• Fractional Distillation Process:

  • vapours rise through a column which is hot at the bottom, and cooler at the top
  • vapours condense when they reach a part of the column that is below the temperature of their boiling point
  • each liquid is led away from the column
• Some properties of hydrocarbons depend on the size of their molecules, including boiling point, viscosity and flammability. These properties influence how hydrocarbons are used as fuels.
• The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water.
• As hydrocarbon length increases:

  • Viscosity (thickness) increases
  • Flammability decreases
  • Boiling point increases

  (and vice versa)
• Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules. Cracking can be done by various methods including catalytic cracking and steam cracking.
• • catalytic cracking uses a temperature of approximately 550 °C and a catalyst known as a zeolite which contains aluminium oxide and silicon oxide
• • steam cracking uses a higher temperature of approximately 850 °C and no catalyst
• Cracking is important for two main reasons:

  • it helps to match the supply of fractions with the demand for them
  • it produces alkenes, which are useful as feedstock for the petrochemical industry
• Alkanes and alkenes both form homologous series of hydrocarbons, but:

  • Alkanes are saturated, since their carbon atoms are joined by single bonds
  • Alkenes are unsaturated, as they contain at least one carbon double bond
• Alkenes will react with bromine water and turn it from orange/brown to colourless. This is the way to test for a double C=C bond in a molecule.
• As a result, alkenes are more reactive than alkanes. Alkenes can take part in reactions that alkanes cannot. For example, ethene molecules can react together to form poly(ethene), a polymer.