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C4h How Pure Is Our Water
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C4h How Pure Is Our Water

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  • 1. C4h How pure is our water? Uses and Purification of Water Different Types of Water Resources • Lakes • Rivers • Reservoirs • Aquifers – an underground water source How is water used in industry? • Coolant – to stop equipment overheating • Solvent • Cheap raw material Pollutants in water sources • Nitrate residues – from fertilisers • Lead compounds – from lead pipes • Pesticide residues – from spraying crops near water sources What is in water before it is purified? • Dissolved salts and minerals • microbes • pollutants • insoluble solids Before water is fit to drink it needs to be purified to remove these substances and any from the list of pollutants. The Purification Process Water is purified in 3 main stages: 1. Sedimentation 2. Filtration 3. Chlorination
  • 2. 1. Sedimentation: Water contains insoluble solids that need to be removed first e.g. sand and soil. This happens in sedimentation tanks. The larger particles settle to the bottom of the tank and the water is run off from the top (see diagram above) 2. Filtration: Some particles are too small and light to settle out in the sedimentation tank e.g. clay. So the water goes through a filter made from layers of grit, coarse sand and fine sand. This traps smaller insoluble particles such as clay. 3. Chlorination: To kill any microbes that may cause disease, a very small quantity of chlorine gas is dissolved in the water. NOTE: Some soluble substances are not removed in the purification process and these may be poisonous!
  • 3. Testing for Dissolved Ions in Water Hardness in water • Some dissolved ions cause water to be “hard” • When you wash your hands with soap the water makes bubbles. We say that the water lathers. • Hard water does not lather well with soap • Soft water lathers very well • The more soap solution needed to lather, the harder the water must be. Experiment to find out which dissolved ions create hard water Solution Volume of soap solution needed for a permanent lather, cm3 sodium chloride 15cm3 magnesium chloride 3cm3 potassium nitrate 1cm3 sodium sulfate 7cm3 magnesium sulfate 10cm3 calcium sulfate 48cm3 Conclusion Explain in as much detail as you can what these results tell you (or answer questions from the practical sheet). Are there any anomalous (odd) results?
  • 4. Uses and Purification of Water Different Types of Water Resources • • • • How is water used in industry? • • • Pollutants in water sources • • • What is in water before it is purified? • • • Before water is fit to drink it needs to be purified to remove these substances and any from the list of pollutants. The Purification Process Water is purified in 3 main stages: 1. 2. 3.
  • 5. 1. Sedimentation: Water contains _____________ solids that need to be removed first e.g. ______ and ________. This happens in _________________________. The larger particles settle to the ______________ of the tank and the water is run off from the top (see diagram above) 2. Filtration: Some particles are too small and light to settle out in the sedimentation tank e.g. clay. So the water goes through a filter made from layers of ________, __________ sand and ____________ sand. This traps ____________ insoluble particles such as clay. 3. Chlorination: To kill any _______________ that may cause disease, a very small quantity of ________________________ is dissolved in the water. NOTE: Some soluble substances are not removed in the purification process and these may be poisonous!
  • 6. Testing for Dissolved Ions in Water Hardness in water • Some dissolved ions cause water to be _____________ • When you wash your hands with soap the water makes bubbles. We say that the water________________. • ______________ water lather well with soap • ______________ water lathers very well • The more soap solution needed to lather, the ____________ the water must be. Experiment to find out which dissolved ions create hard water Solution Volume of soap solution needed for a permanent lather, cm3 sodium chloride magnesium chloride potassium nitrate sodium sulfate magnesium sulfate calcium sulfate Conclusion Explain in as much detail as you can what these results tell you (or answer questions from the practical sheet). Are there any anomalous (odd) results?
  • 7. Testing for Sulphate Ions, SO42- • Fertilisers contain sulphate ions and if they get into water supplies in large quantities they can be harmful. • We need to be able to test water to find out if sulphate ions are present • Sulphate ions make a white precipitate with barium chloride barium chloride + potassium sulphate barium sulphate + potassium chloride (white ppt) barium chloride + sodium sulphate barium sulphate + sodium chloride (white ppt) Testing for Halide Ions, Cl-, Br-, I- Silver nitrate solution is used to test for halide ions:  chloride ions give a white precipitate  bromide ions give a cream precipitate  iodide ions give a pale yellow precipitate silver nitrate + potassium chloride silver chloride + potassium nitrate (white ppt) silver nitrate + potassium bromide silver bromide + potassium nitrate (cream ppt) silver nitrate + potassium iodide silver iodide + potassium nitrate (pale yellow ppt) Higher ONLY You must be able to write balanced symbol equations (given the appropriate formulae)