Skip to content

Water Purification


To test the purity and pH of different water samples.

HOW DOES IT WORK?                                                                           

  Time Allocation: 20 min

The experiments showed and compared the chemical purity and physical purity of the samples tested to distilled water. Distilled water is completely pure H2O, whereas the water samples showed to be anything but. Often drinking water contains minerals and metals which it collected from its environment before being tested. Water purity is dependent on this as well as the methods that were used to make it suitable for consumption. Often additives are present according to the provincial laws and may vary from province to province

Water samples e.g. tap water, water from a local dam, stream, river or bore-hole will be filtered and observed under a microscope, to find solid particles and microscopic life. Water samples will also be tested for the presence of contaminants. Learners have done precipitation reactions with carbonates and chlorides. They also know the difference between acid and bases and the meaning of the term pH.

The test for nitrites (NO2) are based on the formation of the brown complex (FeSO4.NO). In acidic solutions Fe2+ ions reacts with NO2 ions to form nitric oxide or nitrogen monoxide (NO).

2Fe2 + 4H+ + 2NO2  2Fe3+ + 2NO + 2H2O

NO then reacts with FeSO4 to form FeSO4.NO.

Nitrates (NO3-) reacts with concentrated sulphuric acid to form nitric acid. The nitric acid reacts with ferrous sulphate to form nitric oxide. NO then reacts with iron(II)sulphate to form Fe(H2O)5(NO)2+ – known as the brown ring test.



  • Universal indicator paper
  • 0,1 M barium nitrate solution
  • 0,1 M silver nitrate solution
  • 0,1 M iron(II)sulphate solution (FeSO4)
  • 0,1 M nitric acid
  • 1 M sulphuric acid
  • Concentrated sulphuric acid 98%
  • Filter paper
  • Test tubes
  • Pipettes
  • Erlenmeyer flask
  • Funnel
  • Medicine dropper
  • Microscope
  • Different water samples
  • Distilled water


  1. Fold a piece of filter paper and place into a funnel.
  2. Place funnel and filter paper in a conical flask.
  3. Filter a small amount of the water from sample 1 and examine the filter paper to see if any solid has been filtered from the sample.
  4. Note any observations.
  5. Repeat with all the other samples.


  1. Dip a Universal indicator paper strip in each of the water samples.
  2. Record all the observations that can be made from each strip.


  1. Use a pipette to add a few drops of barium nitrate solution to each sample.
  2. If a precipitate forms, confirm that it is a carbonate, by adding a few drops of nitric acid with a new pipette to the solution – note all observations.
  3. Add a few drops of silver nitrate solution to each sample with a new pipette.
  4. If a precipitate forms, confirm that it is a chloride, by adding a few drops of nitric acid to the solution – note all observations.


  1. Fill a test tube with water from the first sample, until it is one quarter full.
  2. Test the pH with universal indicator paper and add a few drops of diluted sulphuric acid with a pipette to ensure that it is slightly acidic.
  3. Fill the test tube with an equal amount of iron(II)sulphate and shake gently until the solutions are mixed.
  4. Note all observations.
  5. Repeat with all the samples.


  1. Fill a test tube with water from sample 1, until it is one quarter full.
  2. Add an equal volume of ferrous sulphate with the pipette.
  3. Allow two to three drops of concentrated sulphuric acid to run down the inside surface of the test tube.
  4. Note any observations.


When working with hot sulphuric acid , be careful. It is corrosive and heats up faster than water , making it much more dangerous if spilt on skin. Wear safety glasses and protective clothing!

  • Treat all chemicals as if they are poisonous – do not taste, smell or touch with bare hands.
  • Concentrated sulphuric(VI)acid is very corrosive.
    1. It reacts violently, becoming very hot, when mixed with water.
    2. It causes severe burns.

Emergency actions

  • In the eye – flood the eye with gently-running tap water for 10 minutes – see a doctor.
  • Swallowed – Wash out the mouth with water. Do not induce vomiting. Sips of water may cool the throat. See a doctor.
  • In the event of any spill, use solid sodium hydrogen carbonate (bicarbonate of soda) to neutralise.
  • Wash hands with soap after handling concentrated sulphuric acid.