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? What colour would this be on universal indicator paper?

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

  - Weigh an empty evaporating basin - Fill with a sample of the water and heat with a

  bunsen burner until all the water evaporates

  - Reweigh any salts left in the evaporating basin and Calculate the mass of solids that were dissolved in the sample
• State how can you purify a sample of water

  Distillation
• Describe how a sample of water can be purified by distillation

  - First test the pH. Add acid/alkali as necessary to obtain pH 7 - Place the water sample in a conical flask and connect the flask to distillation apparatus (including a condenser) - As the water in the flask is heated, it evaporates and enters the condenser as steam - 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?

  Check the pH is still pH 7.

  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