Flame test colors chart

How a flame test works

A clean wire loop, usually nichrome or platinum, is dipped in hydrochloric acid and then in the sample, and held in the hottest part of a blue Bunsen flame. The heat gives electrons in the metal ions extra energy and lifts them to higher energy levels.

When the electrons fall back, they give out that energy as light of particular wavelengths. Each element has its own set of energy levels, so each gives its own color: the same lines that make up its emission spectrum.

Why the test is not always reliable

Sodium is a common impurity and its intense yellow can hide other colors, so potassium’s lilac is often viewed through blue cobalt glass, which blocks the yellow. Some colors look alike, such as the reds of lithium, strontium and radium, and mixtures are hard to read.

The test works best for the alkali metals, the alkaline earth metals and copper. It can suggest which metal is present, but chemists confirm it with other tests or with a spectroscope.

Colors that named elements

Several elements were discovered through the colors of their flames and spectra, and named after them: cesium from the Latin for sky blue, rubidium from the Latin for deep red, thallium from the Greek for a green shoot, and indium from the indigo line in its spectrum.