Flamin’ hot colours!
Back in your school days there was probably an experiment where you placed a small amount of a compound into a flame and observed it’s colour. This is the flame test and depending on the colour observed it can tell you what elements are present.
Scientifically put, A flame test is an analytic procedure used in chemistry to detect the presence of certain elements, primarily metal ions, based on each element’s characteristic emission spectrum. The colour of flames in general also depends on temperature.
The test involves introducing a sample of the element or compound to a hot, non-luminous flame, and observing the colour of the flame that results. The idea of the test is that sample atoms evaporate and since they are hot, they emit light when being in flame.
The flame test is relatively quick and simple to perform, and can be carried out with the basic equipment found in most chemistry laboratories. However, the range of elements positively detectable under these conditions is small, as 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 cause fainter colours to not appear.
|Metal Ion Flame Tests-Click to enlarge|
The table above from www.compoundchem.com shows the range of colours chemicals produce. These tests work better for some metal ions than other; in particular, those ions shown on the bottom row of the infographic are generally quite faint and hard to distinguish. Sodium’s flame colour is also very strong, and can easily mask the colours of other metal ions.
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