RP8 Water Purification

• How can you test the pH of a sample of water?

  Use universal indicator paper or a digital pH probe
• What would you expect the pH of a sample of pure water to be?

  pH 7 - green
• How could you find the mass of salt dissolved in a sample of water?

  1. Weigh an empty evaporating basin

  2. Fill with a sample of the water and heat with a bunsen burner until all the water evaporates

  3. Reweigh any salts left in the evaporating basin and calculate the mass of solids that were dissolved in the sample
• Describe how a sample of water can be purified by distillation

  1. First test the pH. Add acid/alkali as necessary to obtain pH 7

  2. Place the water sample in a conical flask and connect the flask to distillation apparatus (including a condenser)

  3. As the water in the flask is heated, it evaporates and enters the condenser as steam

  4. Cold water around the condenser cools the steam, which condenses to form water before it is collected in a beaker
• How could you test that the water collected from a distillation experiment is pure water?

  1. Check the pH is still pH 7

  2. Determine the boiling point and check it matches that of water (100oC)
• What safety precautions need to be considered when purifying water?

  • Bunsen burner turned off or put on safety flame when not in use, hair tied back
  • Acids/alkalis used for neutralisation so wear safety goggles
  • Clear up any glassware that breaks