Water & The Ever Changing Earth

• ions, dissolved gases, microorganisms and pollutants are all in water
• water treatment process:

  sedimentation ---> filtration ---> chlorination
• sedimentation first uses a screen to remove large particles and then the water is left to set and floc is then added to stick the particles together to make removal easier
• in filtration, the water passes through a series of filters to remove particles but not bacteria. Water first passes through coarse sand and then fine sand. Then chemicals are added to remove dissolved particles like pesticides
• in drought conditions, you can save water by not using hosepipes
• chlorine can kill bacteria but is harmful to humans as it kills cells so only small amounts are added to drinking water
• fluoride kills bacteria and improves oral health, reducing cavities; however, it can cause illnesses such as fluorosis and stomach cancer
• desalination is the removal of salt from water
• distillation and reverse osmosis are examples of desalination
• solute - solid

  solvent - liquid or gas

  solution - dissolved solute and solvent
• miscible is another word for solubility
• a saturated solution means that no more can dissolve
• hard water has either calcium or magnesium ions dissolved in it
• temporary hard water is calcium hydrogen carbonate
• permanent hard water is magnesium/calcium sulphate/chloride
• temporary hard water can be removed by boiling or adding salt
• permanent water can be removed by adding salt or by ion exchange
• equation for creating temporary hard water

  CaCO3 (s) + CO2 (g) + H2O (L) --> Ca(HCO3)2 (aq)
• advantages of hard water

  • good for bones & teeth
  • better for heart
• disadvantages of hard water

  • boiling causes limescale which blocks pipes
  • expensive to repair
• advantages of soft water

  • doesnt cause limescale when boiled, doesnt damage plumbing
• disadvantages of soft water

  • sodium causes heart disease
• limescale is calcium carbonate
• equation of removing temporary hard water (boiling)

  Ca(HCO3)2 --> CaCO3 + H2O + CO2
• testing for hard water - add soap and shake

  hard water = leaves scum & low lather

  soft water = high lather

  boil all samples - add soap again

  temporary will lather

  permanent won't lather
• the shifting of tectonic plates causes earthquakes and volcanoes on earth
• evidence for continental drift

  1. same rock formations
  2. same fossils
  3. fit together like jigsaw puzzle
• why didnt other scientists believe Wegener's continental drift?

  couldnt explain it
• modern theory - plate tectonics

  convection current in mantle produce energy to move plates of crust
• convection current

  1. core heats the mantle, heated rock less dense + rises
  2. hot rocks cool down, more dense so sink
  3. convection current in mantle produce enough force to move tectonic plates in crust
• constructive

  plates move apart, gap filled with magma = new land e.g. mid Atlantic ridge
• destructive

  plates move towards each other, heavier plate pushes up lighter plate creating mountain / volcano e.g. himalayas
• conservative

  plates rub against each other, releasing force creating earthquakes e.g. san andreas fault
• earthquakes and volcanic eruptions are difficult to predict because tectonic plates move very slowly
• how is the atmosphere formed

  1. volcanoes erupting producing a lot of CO2, nitrogen and water vapour
  2. planet cools so water vapour condenses to form oceans. coal and carbon rocks form
  3. green plants evolve so CO2 levels decrease and O2 increase
  4. animals survive on earth as O2 levels enough
• modern atmosphere

  nitrogen: 79%

  oxygen: 21%

  carbon dioxide: 0.04%
• Combustion: increase CO2

  Respiration: increase CO2

  Decomposition: increase CO2

  Photosynthesis: decrease CO2
• consequences of global warming

  • ice melts
  • more extreme weather
• consequences of acid rain

  • dissolves limestone buildings
  • kills plants
  • lowers pH of lakes
• sulphur dioxide can be released by petrol / diesel burn and will dissolve in atmospheric water and fall as acid rain