Using resources

• State some purposes that humans use the Earth's natural resources for:

  • Energy and fuels for warmth
  • Building materials for shelter
  • Food through farming
  • Fuels through transport
  • Materials for clothing
• Why are the Earth's finite resources becoming unstable?

  As the human population is growing quickly, with people arguing that human's that are using up the Earth's finite resources at a rate which is too fast
• What do chemists try to do to provide new products that allow humans to meet their needs in a sustainable way?

  Try to improve agriculture and industrial processes
• Sometime natural products can be supplemented or replaced by...

  Agricultural and synthetic products e.g until 1920, all fertilisers were obtained from natural resources, such as manure
• What process has enabled humans to produce fertilisers from nitrogen in the air, allowing synthetic fertilisers to be produced?

  The Haber process (An industrial process that makes ammonia by reacting nitrogen and hydrogen together)
• What has synthetic fertilisers allowed?

  Intensive farming to become widespread, meaning that we can produce enough food to support the growing population
• Define 'Potable Water'

  Water is safe to drink
• Why is Potable water not pure water?

  Because it almost always contains dissolved impurities
• What has to be ensured that water contains less of to be considered potable and why?

  • Needs to have low levels of dissolved salts and microbes as Dissolved salts can sometimes be harmful for humans
  • Microbes can cause illnesses
• Why is starting with fresh water easier than sea water to make potable?

  • As removing the large amount of sodium chloride present in sea water requires a lot of energy
• What are people in the UK encouraged to conserve when water reserves run low during the summer months?

  Tap water by the use of hosepipe bans
• Rainwater in rivers, lakes and rocks underground contains low levels of..

  Dissolved substances
• State 2 ways in which potable water can be produced by:

  • Passing the water through filter beds to remove insoluble particles
  • Sterilising the water (Methods include chlorine, ozone and ultraviolet light)
• Which method can produce potable water from sea water?

  Desalination
• Desalination can be done by:

  Distillation and reverse osmosis
• State the process of distillation to produce potable water:

  • Sea water is heated until it boils
  • The salt remains in the liquid, and the steam is pure water
  • The steam is cooled and condensed to produce potable water
• Distillation requires a lot of.. to boil the water and to cool the steam down to condense it

  Energy
• During distillation, the waste water is very salty and can be..

  Difficult to dispose of in a sustainable way which does not harm marine ecosystems
• State the process of reverse osmosis to produce potable water:

  • Water is put under high pressure and passed through a membrane which has tiny pores in it
  • The pores allow water molecules through, but prevents most ions and molecules from passing through
• Why does reverse osmosis have a low efficiency?

  As it requires expensive membranes and produces a large volume of waste water
• Q example: Which method of water purification would be best suited to a country in the Middle East which has a large amount of fossil fuel reserves?

  Distillation - The country would be able to use fossil fuels to provide the energy needed at a relatively low cost
• State some examples of pollutants which might be present in waste water:

  • Human waste water - Harmful bacteria and high levels of nitrogen compounds, which can harm aquatic ecosystems
  • Industrial waste water - Harmful chemicals e.g toxic metal compounds
  • Agricultural waste water - Fertilisers or pesticides which can disrupt sensitive ecosystems
• State the stages in sewage treatment:

  1. Screening and grit removal to remove large particles
  2. Sedimentation allows tiny particles to settle out from still water, producing sewage sludge and effluent
  3. The sewage sludge is digested anaerobically by specific bacteria
  4. The effluent is treated with aerobic bacteria to reduce the volume of solid waste
• State the method of analysing water samples

  • For each sample of water given, test the pH meter by using a pH meter or universal indicator with an appropriate colour chart, recording your observations
  • For each sample of water, pour 50cm3 into an evaporating basin. Heat gently over a Bunsen burner, tripod and gauze until no liquid remains.
  • Allow to cool, then weight the evaporating basin again, calculating the mass of the solid that remains in the evaporating basin
• How could you test to see if the distilled water contain sodium and chloride ions?

  • Sodium ions -Yellow colour in a flame test
  • Chloride ions - White precipitate with silver nitrate solution after a small amount of nitric acid was added
• Evaluate the potential hazards in the practical:

  • Acidic or alkaline water samples, can cause irritation to eyes on skin
  • Hot apparatus - Burns