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Flame test
From Wikipedia, the free encyclopedia
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 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.[1] In high-school chemistry courses, wooden splints are sometimes used, mostly because solutions can be dried onto them, and they are inexpensive. Nichrome wire is also sometimes used.[1] When using a splint, one must be careful to wave the splint through the flame rather than holding it in the flame for extended periods, to avoid setting the splint itself on fire.
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 equipment not usually found in a chemistry laboratory. 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.
Although the test only gives qualitative information, not quantitative data about the actual proportion of elements in the sample; quantitative data can be obtained by the related techniques of flame photometry or flame emission spectroscopy.
Contents |
Some common metals and corresponding colors are:
| Symbol | Name | Color |
|---|---|---|
| As | Arsenic | ◼ Blue |
| B | Boron | ◼ Bright Green |
| Ba | Barium | ◼ Light Green |
| Ca | Calcium | ◼ Brick red (the color red that bricks generally are) |
| 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 | Violet |
| Li | Lithium | Crimson |
| Mg | Magnesium | Brilliant white |
| Mn(II) | Manganese(II) | Yellowish green |
| Mo | Molybdenum | Yellowish green |
| Na | Sodium | Intense yellow |
| P | Phosphorus | Pale bluish green |
| Pb | Lead | White/blue |
| 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 sulfate |
 Flame test on copper sulfate seen through cobalt glass |
 Flame test on sodium carbonate |
 Flame test on sodium carbonate seen through cobalt glass |
- ^ a b Jim Clark (2005). Flame Tests. Chemguide.
- 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