< 9-1 Chemistry
Flame tests can be used to identify some cations (positive ions).
Flame tests
| Compound | colour of flame | Photo |
|---|---|---|
| Lithium | Crimson flame |  |
| Sodium | Yellow flame |  |
| Potassium | Lilac flame |  |
| Calcium | Orange-red flame |  |
| Copper | Green flame |  |
If a sample containing a mixture of ions is used, some flame colours can be masked.
Metal hydroxides
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.
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