Identifying ions

• Aim:to identify ions in unknown salts, using the tests for the specified postive and negative anions
• stepp 1: carry out one or more tests on each salt, you may need to dissolve a sample of salt in distilled water if you are given solids rather than solutions
• step 2: record your observations carefully, repeat any tests that do not get clear results
• flame tests:

  1. dip a clean wire loop into a solid sample of the compound being tested
  2. put the loop into the edge of the blue flame from a Bunsen burner
  3. observe and record the flame colour produced
• flame test colours;

  crimson= lithium (Li+)

  yellow= sodium (Na+)

  lilac = potassium (K+)

  orange-red= calcium (Ca2+)

  green = copper (Cu2+)
• hydroxide precipitates test:

  Add a few drops of dilute sodium hydroxide solution. Observe and record the colour of any precipitate formed.
• Hydroxide precipitates colours :

  White - dissolves in excess hydroxide solution = aluminium (Al3+)

  White- no change in excess hydroxide solution = calcium (Ca2+)

  White- no change in excess hydroxide solution = Magnesium, (Mg2+)

  Blue = copper (Cu2+)

  Green= iron (II), (Fe2+)

  brown= Iron(III), Fe3+
• Test for carbonate ions

  Add a few drops of dilute hydrochloric acid. Bubbles are produced if carbonate ions are present. Confirm that the gas is carbon dioxide - limewater turns milky/cloudy.
• Test for sulfate ions

  Add a few drops of dilute hydrochloric acid, then a few drops of barium chloride solution. A white precipitate forms if sulfate ions are present.
• Test for halide ions

  Add a few drops of dilute nitric acid, then a few drops of silver nitrate solution. Observe and record the colour of any precipitate formed.

  White = chloride, Cl-

  Cream = bromide, Br-

  Yellow= iodide, I-