How to Test for Cations (Edexcel IGCSE Science)

Tests for Cations

Spec point — 6.18

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

Exam Hint Sometimes you may not see much of a precipitate because the cation you are testing is present is very small amounts. However, every a slight cloudiness or colour change can indicate a positive test result.