Flame TestsOxford AQA IGCSE Chemistry: Revision notes
Section 1
What is a flame test used for?
A flame test can be used to identify the metal ion present in a compound. When certain metal compounds are heated strongly in a flame, the metal ion produces a characteristic flame colour, which can be used to identify it.
Section 2
What are the flame colours of common metal ions?
You need to recall these flame colours:
| Metal ion | Flame colour |
|---|---|
| Lithium | Crimson |
| Sodium | Yellow |
| Potassium | Lilac |
| Calcium | Red (brick-red) |
| Barium | Green |
Each metal produces a distinct, recognisable colour, which is why flame tests are a reliable identification method.
Students often mix up lithium (crimson) and calcium (red) — both are reddish, but crimson is a deeper, more purple-red than calcium's brighter red.
Section 3
How is the required practical carried out?
The required practical for this topic is to identify the metal ion in an unknown compound using flame testing techniques.
- Clean a piece of equipment (such as a nichrome wire loop) thoroughly, often by dipping it in dilute acid and rinsing.
- Dip the clean wire into a sample of the unknown compound.
- Hold the wire in a roaring blue Bunsen flame.
- Observe and record the flame colour produced.
- Compare the observed colour with known flame colours to identify the metal ion.
Always mention cleaning the equipment between tests — contamination from a previous sample is a common source of error the examiners expect you to identify.
Must Know
- Flame tests identify metal ions by the colour they produce when heated
- Lithium: crimson
- Sodium: yellow
- Potassium: lilac
- Calcium: red
- Barium: green
- The required practical uses this technique to identify the metal ion in an unknown compound
That's the notes covered.
Carry on to the next subtopic.