Flame tests can be conducted in several ways, either by using solid compounds or solutions of compounds being tested. Either way, the aim of the lesson is the same.
Students burn a tiny sample of a solution or solid compound using a flame test loop. The loops can be made of twisted nichrome wire fixed into the end of a suitable handle, usually a length of wooden dowel. The best flame test loops are made from platinum wire but is usually far too expensive for most schools to use.
With nichrome flame loops, a trace of orange flame is usually visible when heated in a Bunsen flame. If you take this into account before you test the compounds, it can easily be ignored.
Flame test loops can be purchased from most lab supply companies.
Students usually dip the loop into dilute hydrochloric acid and then heat it in a blue Bunsen flame first to clean it. When clean, and cool they may then dip the loop into the acid again and then into a powdered compound or solution and then back into the flame.
Each compound in the table below produces a different coloured flame. Some are vibrant whereas others are more subtle.
| Li |
red |
| Na |
orange |
| K |
lilac (pink) |
| Rb |
red /violet |
| Cs |
blue /violet |
| Ca |
orange-red |
| Sr |
red |
| Ba |
pale green |
| Cu |
Blue / green |
| Pb |
greyish-white |
Equipment required (per set):
- Bunsen Burner
- Dilute HCl
- Selection of compounds (powdered or solutions of)
- Flame test loop
Flame tests can be useful in identifying unknown solution precipitates.