The flame testing is a method used in chemistry to detect the presence of certain ions, primarily metal ions, based on each element’s characteristics emission spectrum. The colour of the flames normally depends on the temperature. Different types of Bunsen burner with flame types depend on the oxygen supply. The flame of rich fuel with no premixed oxygen produces a yellow diffusion flame. The flame of lean fully oxygen premixed flame produces no soot and the flame colour is produced by molecular radicals, especially in CH and C2 band emission.
Flame testing involves using a nichrome wire loop to introduce a sample into a quiet blue Bunsen flame. Many cations show characteristic colours.
The nichrome wire is easily contaminated and was cleaned by dipping it into concentrated hydrochloric acid and heating vigorously with a roaring Bunsen flame. The wire is clean when it gives no colour with the flame.
Result of flame testing cations:
|Cation Tested |Colour of Flame | |Barium |apple green | |Calcium |brick red | |Potassium | lilac | |Copper |greeny/ blue | |Sodium | orange |
Our CaCO3 sample only showed a positive result for sodium. i.e. the sodium flame test dominated. This may have been due to incomplete washing...