Chemistry 2.3

• Bacoating water from different sources

  1. Filter

  2. Sedimentation

  3. Chlorine added
• Reasons for water filtration

  • To be pure enough for us to drink
  • To survive
• Steps in water filtration

  • Screen
  • Course Filter
  • Sedimentation
  • Pump
  • Filter
  • Storage tank
• What is removed at each step

  • Screen - trees, leaves, fish sticks, litter, grit, large items
  • Course filter - small rocks, debris, large insoluble particles
  • Sedimentation tank - clumps, sludge, large insoluble particles, finer insoluble particles
  • Chlorine added - Harmful bacteria
• Water composition


  • Dissolved gases - carbon dioxide (CO2), oxygen (O2)
  • Ions - Sodium (Na+), calcium (Ca+2), magnesium (Mg+2), potassium (K+)
  • Bacteria and viruses
  • Fertilizers and pesticides
• Bacteria and viruses in water can make you ill if you drink them and the water is not filtered
• Waste and pollutants from factories end up in rivers and are harmful to humans
• Fluorine


  Present in toothpastes and stops tooth decay
• DMFT


  Decayed, Missing or Filled Teeth
• Fluoridation


  1. Fluoride is added to water to help with teeth decay

  2. Fluoride decreases enamel decay

  3. Fluoride prevents cavities, especially in children under 12

  4. Fluoride is naturally occurring in drinking water
• Evidence for fluorine in water

  • Fluoride decreases enamel decay
  • Fluoride prevents cavities, especially in children under 12
  • Fluoride is naturally occurring in drinking water
• Evidence against fluorine in water

  • Too much fluoride causes fluoridesis (ugly, brown, mottling of the teeth)
  • Fluoride can disrupt some of the enzymes in your body
  • Giving fluoride to pregnant rats can cause holes in the unborn brains
• Desalination


  A special type of simple distillation used in countries that can't rely on fresh water in rainfall, but sea water which contains salts
• Desalination process


  1. Sea water is heated, which turns the water into a gas

  2. The gas rises and is condensed on a plastic cover

  3. The condensed water flows down the plastic cover into a second container, leaving the salts behind in the first container
• Positive benefits of desalination


  • Provides clean water to very arid (dry) parts of the world
  • Makes very pure water
• Negative benefits of desalination

  • Expensive
  • Energy intensive (needs a lot of energy)
  • Contributes to climate change
• Hard water


  Contains dissolved ions of magnesium and calcium, due to the water being in contact with limescale and other calcium compounds
• Soft water


  Doesn't contain the dissolved magnesium and calcium ions
• Advantages of hard water

  • Some people prefer the flavour
  • Some brewers/bakers prefer using hard water
  • Helps reduce heart disease and strengthens children's teeth and bones
• Disadvantages of hard water

  • Difficult to form a lather with soap, causing soap waste and scum to form
  • Limescale forms within appliances that heat up water, making them less efficient/causing them to break
  • Hot pipes become 'furred up' and blocked
• Temporary hard water


  Contains dissolved calcium hydrogen carbonate (Ca(HCO3)2) or magnesium hydrogen carbonate (Mg(HCO3)2), which breaks down when boiled
• Permanent hard water


  Contains dissolved calcium sulfate (CaSO4) or magnesium sulfate (MgSO4), which don't break down when boiled