Flame test
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The flame test is a procedure used in chemistry to detect the presence of certain metal ions, based on each element's characteristic emission spectrum. The color of flames in general also depends on temperature; see flame color.
The test involves introducing a sample of the element or compound to a hot, non-luminous bunsen flame, and observing the colour that results. Samples are usually held on a platinum wire cleaned repeatedly with hydrochloric acid to remove traces of previous analytes. In high-school chemistry courses, wooden splints are used, mostly because solutions can be dried onto them, and they are inexpensive. When using a splint, one must be very careful not to light the splint itself on fire by waving the splint through the flame rather than holding it in the flame for extended periods.
Sodium is a common component or contaminant in many compounds and its spectrum tends to dominate over others. The test flame is often viewed through cobalt blue glass to filter out the yellow of sodium and allow for easier viewing of other metal ions.
The flame test is fast and easy to perform, and does not require any special equipment. However, the range of detected elements is small, and the test relies on the subjective experience of the experimenter rather than any objective measurements. The test has difficulty detecting small concentrations of some elements, while too strong a result may be produced for certain others, which tends to drown out weaker signals. Finally, the test only gives qualitative information, not quantitative data about the actual proportion of elements in the sample.
[edit] Common metals
Some common metals and corresponding colors are:
| Symbol | Name | Color |
|---|---|---|
| As | Arsenic | Blue |
| B | Boron | Bright Green |
| Ba | Barium | Light green |
| Ca | Calcium | Red-orange |
| Cs | Cesium | Pale violet |
| Cu(I) | Copper(I) | Blue |
| Cu(II) | Copper(II) (non-halide) | Green |
| Cu(II) | Copper(II) (halide) | Blue-green |
| Fe | Iron | Gold |
| In | Indium | Blue |
| K | Potassium | Lilac |
| Li | Lithium | Crimson |
| Mn(II) | Manganese(II) | Yellowish green |
| Mo | Molybdenum | Yellowish green |
| Na | Sodium | Intense Yellow |
| P | Phosphorus | Pale bluish green |
| Pb | Lead | Pale green |
| Rb | Rubidium | Pale violet |
| Sb | Antimony | Pale green |
| Se | Selenium | Azure blue |
| Sr | Strontium | Crimson |
| Te | Tellurium | Pale green |
| Tl | Thallium | Pure green |
| Zn | Zinc | Bluish green |
 Gas flame |
 Gas flame seen through cobalt glass |
 Flame test on copper sulphate |
 Flame test on copper sulphate seen through cobalt glass |
 Flame test on sodium carbonate |
 Flame test on sodium carbonate seen through cobalt glass |
[edit] External links
- Flame Test - Colouring Fire - Pictures of Several Flame Tests, Includes Instructions
- WebMineral.com - Flame Coloration by Element
- All Info About Chemistry - How to Do Flame Tests
