What is the colour of the flame of sodium and potassium?

Answer: The two most significant factors affecting the flame’s colour are black-body radiation and spectral band emission. In the most familiar type of flame, hydrocarbon flames, oxygen availability, and the degree of fuel-oxygen pre-mixing have the most significant impact on colour. A flame test is a chemical analytical technique that identifies the presence of particular elements, usually metal ions, using each element’s distinct emission spectrum.

A specimen of the element or compound is subjected to a hot, non-luminous flame as part of the test, and the colour of the flame that emerges is observed. The test assumes that sample atoms vaporise and emit light when exposed to the flame because they are heated.

A Lilac (purple) colour is observed for potassium, which is not visible through cobalt glass. For sodium, intense yellow colour is observed, which is visible through cobalt blue glass.