C4 Lesson 16 – Testing Water

After studying this topic, you should be able to: recall the tests for sulfate ions and halide ions in water write word equations for precipitation reactions write balanced symbol equations for precipitation reactions C4 Lesson 16 Testing water

Water contains... Insoluble material Microbes Pollutants Dissolved salts and minerals We can test for the presence of some of the dissolved salts and minerals

Testing for sulphate ions Barium chloride solution is used to test for dissolved sulphate ions. A small sample of the water is put into a test tube, then a few drops of barium chloride solution are added. If sulfate ions are present then a white precipitate of barium sulphate forms. For example: Sodium sulphate + barium chloride  sodium chloride + barium sulphate (white precipitate) Na 2 SO 4 + BaCl 2  2NaCl + BaSO 4

Testing for halide ions Silver nitrate solution is used to test for dissolved halide ions. These include chloride ions, bromide ions and iodide ions. A small sample of the water is put into a test tube, then a few drops of silver nitrate solution are added. Different coloured precipitates form. Chloride ions produce a white precipitate. Bromide ions produce a cream-coloured precipitate. Iodide ions produce a pale yellow precipitate e.g. sodium chloride + silver nitrate  sodium nitrate + silver chloride (white precipitate) NaCl + AgNO 3  NaNO 3 + AgCl