Flame tests for metal ions
Different metal Electrically charged particle, formed when an atom or molecule gains or loses electrons. produce different flame colours when they are heated strongly. This is the basis of a A qualitative identification technique where samples are heated and the metal ions present are identified by characteristic flame colours.. In order to confidently identify which ion is present, the result for a test should be unique, and not caused by another ion.
To carry out a flame test:
- dip a clean wire loop into a solid sample of the compound being tested
- put the loop into the edge of the blue flame from a Bunsen burner
- observe and record the flame colour produced
The table shows the flame test colours for five common metal An atom or group of atoms that have lost electrons and become positively charged. Most cations are formed from metals.:
| Ion present | Flame test colour |
| Lithium, Li+ | Crimson |
| Sodium, Na+ | Yellow |
| Potassium, K+ | Lilac |
| Calcium, Ca2+ | Orange-red |
| Copper, Cu2+ | Green |
| Ion present | Lithium, Li+ |
|---|---|
| Flame test colour | Crimson |
| Ion present | Sodium, Na+ |
|---|---|
| Flame test colour | Yellow |
| Ion present | Potassium, K+ |
|---|---|
| Flame test colour | Lilac |
| Ion present | Calcium, Ca2+ |
|---|---|
| Flame test colour | Orange-red |
| Ion present | Copper, Cu2+ |
|---|---|
| Flame test colour | Green |
If a mixture of ions is present, some of the flame colours may not be clearly visible. For example, the yellow colour from sodium ions is very intense and tends to hide the paler lilac colour from potassium ions.
Worked example
A sample of an ionic compound produces an orange-red flame test colour. Identify the metal ion present.
The metal ion is calcium, Ca2+.
