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Flame test



 

Additional recommended knowledge

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.

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 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

See also

References

  1. ^ a b Jim Clark (2005). Flame Tests. Chemguide.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Flame_test". A list of authors is available in Wikipedia.
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