c6- GLOBAL CHALLENGES

• how water is purified:

  1. filtration: a wire mesh screens out large things and then (after sedementation) a sand and gravel bed filters out any other bits
  2. sedimentation: iron/ aluminum sulfate is added to water, which makes fine particles clump together and settle at bottom
  3. chlorination: chlorine gas is added to kill harmful bacteria and other microbes
• how salt water is treated:

  • dissolved salts are removed via DESALINATION

  for large scale desalination, simple distillation is used, which uses a lot of energy and can therefore be expensive
• air pollutants are substances released into the atmosphere that may harm living things

  released as a result of burning fossil fuels
• carbon monoxide (CO)

  produced by: incomplete combustion of carbon based fuels

  harmful as: its a toxic gas, prevents oxygen from binding to haemoglobin
• carbon particulates (C)

  produced by: incomplete combustion of carbon based fuels

  harmful as: causes respiratory problems, makes surfaces black and dirty
• nitrogen monoxide (NO)

  produced: at high temps, the nitrogen and oxygen in the air react together

  harmful as: quickly oxidises to form nitrogen dioxide
• nitrogen dioxide (NO2)

  harmful as: causes respiratory problems, causes acid rain which corrodes buildings/ kills plants and aquatic life
• sulphur dioxide (SO2)

  produced by: sulfur impurities in fuel burns, volcanoes

  harmful as: causes respiratory problems, causes acid rain which corrodes buildings, kills plants and aquatic life
• the enhanced greenhouse effect:

  • the release of additional greenhouse gases (carbon dioxide and methane) by human acitvities.
  • this is has the potential to cause average temperature on earth to rise
  • this global warming leads to melting ice caps and rising sea levels, and to climate change
  • climate change brings altered and weather patterns
• greenhouse gas emissions can be reduced by:

  • reducing consumption of fossil fuels by using biofuels
  • using renewable energy resources
  • stopping carbon dioxide escaping when fuels are burnt by carbon capture
• the greenhouse effect is a natural phenomenon that keeps the earth and its atmosphere warm enough for living things to exist
• greenhouse effect:

  A) infared radiation from the sun hits the earth's surface

  B) IR warms the earth's surface

  C) IR is emitted by the surface

  D) greenhouse gases emitt IR in all directions, warming ap

  
• there is a casual correlation between carbon dioxide and global temperature, as if there are more carbon dioxide molecules in the atmosphere, more infared heat will be trapped
• formula for alkenes homoglous group: CnH2n+2
• seperation of crude oil through fractional distillation:

  1. oil is heated and pumped into the bottom of the fractioning column, where it is vapourised
  2. the column is very hot at the bottom but much cooler at the top. As the vapourised oil rises, it cools and condenses
  3. heavy fractions which have stronger inter molecular forces and higher boiling points condense near the bottom.
  4. lighter fractions have weaker inter molecular forces and lower boiling points condense further up the column.
• factors that affect decisions on recycling:

  • how easy it is to collect and sort the waste
  • the cost of recycling compared to burning the product or sending it to landfill
  • amount of energy required at each stage
• electrolysis is used to extract some metals from their ores because they are too reactive to be reduced by carbon
• electrolyisis is used to extract aluminium by:

  1. aluminum oxide is mixed with a cryolite to lower it's MP
  2. layer of graphite around inside of cells forms the negative electrode.
  3. in cell, the mixture of aluminum oxide and cryolite is melted and ca current is passed.
  4. molten Al formed at negative electrode, where aluminum ions are reduced to Al atoms. liquid Al goes to bottom where it's tapped off
  5. at + electrode, the oxygen ions are oxidised and form oxygen gas
  6. graphite in + electrodes react with oxygen, producing carbon dioxide & so electrodes must be replaced regularly
• a life cycle assessment is a part of a legislation put into place to help protect the environment
• the point of a life cycle assessment is to make companies consider their use of natural resources and minimise the environmental impact their product has
• main stages of a life cycle assessment:

  1. making materials for the product from the raw materials needed
  2. manufacturing the product
  3. transport of the product and raw materials
  4. using the product
  5. disposing of the product at the end of its life
• bioleaching is a biological method of extraction in which bacteria speeds up reactions that release soluble metal compounds from metal sulfides
• advantages of bioleaching:

  • cheaper than other methods
  • bacteria occur naturally
  • allows extraction from low grade ores
• disadvantages of bioleaching:

  • slow
  • toxic substances can be produced
  • risk of sulfuric acid which can damage the environment
• phytoextraction is a biological method of extraction in which plants absorb metals through their roots and concentrate them in their cells
• advantages of phytoextraction

  • cheaper
  • produces less waste
  • involves smaller energy transfers
  • closer to being a carbon-neutral activity
• disadvantages of phytoextraction:

  • slow
  • crops may need replanting and harvesting before available metal is removed
• high grade ore= high concentration of metal

  low grade ore= low conc of metal
• extraction of metals by heating with carbon:

  • any metal below carbon on the reactivity series can be extracted from its metal compound by heating with carbon or carbon monoxide
  • this is an example of redox reaction
• cracking is the process of the breaking down of larger less useful alkanes and alkenes using heat and catalyst
• the development of plants that photosynthesis removed carbon dioxide from the atmosphere and added oxygen
• water vapour condensed into liquid water as the earth cooled
• carbon dioxide dissolved in the newly formed oceans, removing it from the atmosphere
• earth's atmosphere keeps the earth warm due to the greenhouse effect

  greenhouse gases prevent infrared radiation from escaping into space
• global warming occurs when there are more greenhouse gases than usual in the atmosphere which traps even more heat