Tests for Cations

Tests for Cations

• Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide and ammonia
• If only a small amount of NaOH is used then normally the metal hydroxide precipitates

Analysing results

• The table below contains the results for each of the cations included in the syllabus
• If a precipitate is formed from NaOH then the hydroxide is insoluble in water

Method:

• Add a few drops of dilute sodium hydroxide (NaOH()aq) into an unknown solution and observe any changes.
  • We can test further by adding excess NaOH()aq and recording any changes.
• Add a few drops of dilute ammonium hydroxide (NHOH()4aq) into an unknown solution and observe any changes.
  • We can test further by adding excess NHOH()4aq and recording any changes.

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