4.10 CHEMISTRY

• Finite resources are resources being used up faster than they are being replaced. There is a limited amount
• Renewable resources are resources that can be replaced at the same rate they are being used up
• List of finite and renewable resources

  • coal - finites
  • cotton- renewable
  • natural gas - finite
  • leather - renewable
  • metal- finite
  • crude oil- finite
  • nuclear fuels - finite
  • wood- renewable
  • ethanol( produced by fermentation) - renewable
  • solar power - renewable
• Humans use earths resources to provide

  • warmth
  • shelter
  • food
  • transport
• natural resources provide

  • food
  • timber
  • clothing
  • fuels
• Natural resources are supplemented by agriculture( farming crops and animals)
• Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
• Chicken is an example of a natural resource for food. It is supplemented by agriculture with chicken farms, warmth
• Wheat crop is another example of a crop that is a natural resource that we use as food., the agricultural supplements that go with this are fertiliser to increase the amount of crop yield
• Recently, chemists have provided new synthetic products which supplement/replace natural products

  This can help reduce our reliance on natural products
• For example cotton is a natural resource that is used for clothing, so when chemists produce a new product, the synthetic product in this case polyester, will replace the natural product
• potable water is drinking water
• Potable water should have low levels of

  • Dissolved salts
  • Microbes
• Most drinking water contains some dissolved salts but pure water does not contain any salt
• 
  

  Rainwater dissolves some gases from the air as it falls to the ground and obtained from rainwater, groundwater, and surface water. Also, known as freshwater
• Obtaining potable water from ground water sources :

  1. Choosing an appropriate source of fresh water
  2. Passing the water through filter beds--> using mesh to remove large particles and using sand + gravel filtration to remove small solid particles
  3. Sterilizing(killing organisms)
• Sterilizing involves:

  • chlorine
  • ozone
  • ultra violet(UV)
  • THESE ARE ALL CALLED STERILISING AGENTS
• If fresh water supplies are limited, then we may have to desalinate salty water and/or sea water
• Desalination is the process of removing salt from seawater by distillation and is done by

  • distillation
  • using membranes (reverse osmosis)
• Distillation separates mixtures with different boiling points

  and it separates the salt from pure water
• Both distillation and reverse osmosis require large amounts of energy which can be quite expensive
• In distillation energy is needed to boil the water

  In processes using membranes, energy needed to pressurize the water
• Urban lifestyles and industrial processes produce large amounts of waste water. This waste water requires treatment before being released into the environment
• Sewage and agricultural waste water requires the removal of:

  • organic matter
  • Harmful microbes
  • Industrial waste water water requires the removal of
  • organic matter
  • harmful chemicals
• Sewage treatment process 1- screening and grit removal

  • Screening removes large solid particles(eg grit) by passing the sewage through a screen
• Sewage treatment process 2- sedimentation

  • Sedimentation is used to produce sewage sludge and an effluent
  • Sedimentation allows the small solid particles( sediment) to sink to the bottom of the tank forming sewage sludge while the liquid effluent remains above
• sewage treatment process 3- Anaerobic digestion of sewage sludge


  The sewage sludge is dried and anaerobically digested, (broken down by micro-organisms in the absence of 02)

  The digestion of sewage sludge removes organic matter. It produces biogas used to make electricity

  Dried sludge can be used as fertiliser
• Sewage treatment process 4- Aerobic biological treatment of effluent

  The effluent is aerobically digested (broken down by microorganisms in the presence of oxygen ). This removes organic matter and harmful microbes
• Corrosion


  Destruction of materials by chemical reactions with substances in the environment
• Corrosion


  • Rusting
• Conditions for iron to rust

  • Both air and water are necessary
• Corrosion prevention


  Applying a coating that acts as a barrier, such as greasing, painting or electroplating
• Corrosion prevention


  • Aluminium has an oxide coating that protects the metal
  • Zinc is used to galvanise iron (sacrificial protection)
• Sacrificial protection


  The more reactive metal donates electrons to any ions of the other metal that may have formed so they don't corrode
• Alloys


  • Most metals in everyday uses are alloys
  • Pure metals are too soft for everyday uses
• Alloys


  • Gold in jewellery is usually an alloy with silver, copper and zinc
  • Bronze is an alloy of copper and tin
  • Brass is an alloy of copper and zinc
  • Steels are alloys of carbon and iron
• Steels


  • Low-carbon steels are easily shaped, used for sheeting
  • High carbon steels are hard, used for cutting tools
  • Stainless steels (containing chromium and nickel) are resistant to corrosion, used for cutlery
• Aluminium alloys


  • Low density, used for aircraft
• Soda-lime glass


  Made by heating a mixture of sand, sodium carbonate and limestone (most commonly used glass)
• Borosilicate glass


  Made from sand and boron trioxide, melts at higher temperatures than soda-lime glass it is mainly used for oven ware