9-1 Chemistry/Identification of ions

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Flame tests can be used to identify some cations (positive ions).

Flame tests[edit | edit source]

Compound colour of flame Photo
Lithium Crimson flame
Sodium Yellow flame
Potassium Lilac flame
Flame Test K.jpg
Calcium Orange-red flame
Copper Green flame
Copper flame test.JPG

If a sample containing a mixture of ions is used, some flame colours can be masked.

Metal hydroxides[edit | edit source]

Sodium hydroxide solution can be used to identify some cations:

  • Aluminium
  • Calcium
  • Magnesium

Ions form white precipitates when sodium hydroxide solution is added but only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution.