C4h- Purifying and Testing Water

C4h- Purifying and Testing Water

1. In the UK, water resources include:

   • Lakes
   • Rivers
   • RESEVOIR: An artificial lake, made by building a dam to accumulate and save river water in the valley behind.
   • AQUIFER: An underground layer of permeable rock, gravel or sand which is soaked with water.

2. Why is it Important to conserve Water?

   • It is a very important resource for many industrial chemical processes -A solvent to dissolve other substance, A coolant to stop overheating happening, A cheap raw material
   • FRESH WATER is a limited resource. Only 3% of the Worlds water is fresh. Over-use of water, especially in dry weather, can lead to water shortages and hosepipe bans. Conserving water also saves the materials and energy needed to treat and transport it.

3. Pollutants in Drinking Water

   • Nitrates: It comes from fertiliser that runs off from agricultural fields to water resources
   • Lead Compounds: It comes from old lead pipes
   • Pesticides: It comes from spraying the crops in the field close to water resources

4. Water Purification Process

   • SEDIMENTATION: Removes large suspended particles
     • FILTERATION: Removes small suspended particles
       • CHLORINATION: Kills microbes in the water
   • Some soluble substances are not removed from water during purifications because they may be poisonous, so strict limits are placed on how much of them can be in the water.
   • Distillation
     • This process can produce very pure water. However, a lot of energy is needed to do this. Therefore, it is very expensive to produce large quantities of water in this way

5. Testing for Sulphate Ions in water

   • This is a PRECIPITATION REACTION
   • BARIUM CHLORIDE SOLUTION is used to test for DISSOLVED SULPHATE IONS
   • If sulphate ions are present then a white precipitate of barium sulphate is formed
   • Sodium Sulphate + Barium Chloride --> Sodium Chloride + Barium Sulphate (White Precipitate)
   • Na2SO4 + BaCl2 --> 2NaCl + BaSO4

6. Testing for Halide Ions

   • This is a PRECIPITATION REACTION
   • SILVER NITRATE SOLUTION is used to test for DISSOLVED HALIDE IONS (e.g. chloride ions, bromide ions, iodide ions)
   • Chloride- White
   • Bromide- cream
   • Iodine- Pale Yellow
   • Sodium Chloride + Silver Nitrate --> Sodium Nitrate + Silver Chloride (White Precipitate)
   • NaCl + AgNO3 --> NaNO3 + AgCl