Core Chemistry Summary

C1 - Air Quality

  • The three main stages in the evolution of the atmosphere were volcanic activity, evolution of green plants and evolution of complex organisms
  • The atmosphere today contains mainly nitrogen (78%), oxygen (21%) and argon (1%)
  • Human activity is changing the atmosphere by adding pollutants
  • Chemical reactions happen when atoms are rearranged but reactants and products have different properties
  • Fossil fuels are hydrocarbons and when they burn it is an oxidation reaction, producing mainly CO2
  • Types of carbon pollution include carbon dioxide (a greenhouse gas), carbon monoxide (a poisonous gas) and particulates (which causes breathing problems and makes buildings dirty)
  • Sulfur pollution comes from impurities in fuels, making sulfur dioxide and causing acid rain
  • Nitrogen pollution involves nitrogen from the air; nitrogen oxides form and cause acid rain
  • Pollution from power stations can be reduced by wet scrubbing the flue gases
  • Pollution from cars can be reduced by using more efficient engines, catalytic converters, regular MOT tests and using public transport
  • We could also use other fuels like biofuels, which are carbon neutral, or use electric cars
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C2 - Material Choices

  • All materials are made up of chemicals but some occur naturally whilst others are synthetic
  • Important properties to consider of materials include melting point, tensile and compressive strength, stiffness, hardness and density
  • Uses for materials depend on their properties, and their properties depend on what they're made of
  • E.g. rubber is strong, flexible and mouldable so it is good for car tyres
  • Crude oil is a mixture of hydrocarbons; hydrocarbons properties change as the chain gets longer
  • In crude oil, there are strong covalent bonds within each hydrocarbon molecule and intermolecular forces of attraction between different hydrocarbon molecules
  • The longer a hydrocarbon chain is, the stronger the intermolecular forces, and so the higher the boiling point
  • Therefore, hydrocarbons in crude oil can be separated by fractional distillation
  • Crude oil can supply fuels, lubricants and hydrocarbons which are synthesised to new, more useful compounds
  • Polymerisation is the joining of lots of small monomers to form a long molecule called a polymer
  • Polymers have lots of different properties and have replaced some natural materials, e.g. rigid PVC has replaced wood for window frames
  • Polymers properties depend on their molecular arrangement, how the chains are held together and if they have been modified to change their properties
  • Nanoparticles modify materials' properties due to their large surface-area-to-volume ratio
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C3 - Chemicals in our Lives

  • Magnetic clues in rocks and sedimentary rocks give evidence for continental drift
  • The crust contains different minerals e.g. sedimentary rocks limestone and coal and salt from evaporation
  • Salt is found in underground deposits and can be obtained by physical extraction or solution mining
  • In hotter countries, salt can be obtained by evaporating seawater which produces the purest salt
  • Salt is important in food production to add flavour and as a preservative
  • However, too much salt can increase the risk of high blood pressure, stomach cancer and osteoporosis
  • The Government issues guidelines for salt intake, carries out risk assessments and advises the public
  • Electrolysis of salt solution produces hydrogen (e.g. for ammonia), chlorine (e.g. for killing bacteria) and sodium hydroxide (e.g. for soap)
  • Large scale electrolysis has an environmental impact; it uses lots of energy and uses mercury and asbestos
  • In the UK our water is chlorinated to make it safe by killing bacteria,
  • Chlorine can be made by electrolysis of brine or oxidation of hydrogen chloride
  • Chlorine can form chlorinated hydrocarbons with organic compounds in water, which can be carcinogenic
  • Lots of products can be made using chemistry, but some chemicals can stay in and harm the environment
  • Life Cycle Assessments consider the materials, manufacture, use and disposal of products
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