Metal Flame Emission

Flame testing is an analytical technique where a sample is applied to a flame, and the characteristic emission spectrum is used to identify different elements. When this technique is used to identify metal species, it is called metal flame emission testing. When sufficient energy is applied to some metals through a hot flame, they emit light with a characteristic wavelength or color. You can clearly see this phenomenon when watching a fireworks display.

Different metals emit different colors. Thus, we can use the color of the emitted light to determine the metal present. But before we dive into the technique further, let's take a step back. Atoms have multiple energy levels for their electrons, which are different for each element.

When an electron is at its lowest possible energy level, it is said to be at its ground state. When an atom absorbs energy, it gets excited, and electrons in the atom move from the ground state to a higher energy level. When the electrons relax back down to a lower state, or the ground state, the excess energy gained is released in the form of emitted light.

The wavelength of the emitted light depends on the energy level that the electron was excited to and the level that it relaxes back to. This emitted wavelength, or color of light, is specific to the atom present and is used to identify a metal sample in the metal flame emission test.

In the metal flame emission test, we apply a metal sample to a hot flame and observe the color of the emitted light. For example, barium will emit a yellowish-green color in the flame, while copper emits blue-green and potassium a pinkish-purple.

Now, a sample actually consists of the metal, metal ions, metal oxides, metal hydroxides, and metal salts. And since atoms and molecules absorb and release energy differently, the emitted light actually contains a range of wavelengths and intensities forming an emission spectrum.

A spectrophotometer is used to measure the range of wavelengths of emitted light. 

In this lab, you'll use the metal flame emission test to identify various metals and then analyze the emitted and absorbed light using a spectrophotometer.