Why are salts used in flame testing?

Answer

Bye Beau

The reason why one uses salts, usually still in solution, is of a practical nature.

In this test you must:

• getting the material into the flame, preferably finely divided, that is more difficult with a piece of metal. Spraying metal powder produces dust and that is not very healthy, so it is best to use something liquid. What is possible is to put pure metal salt on an (inert) metal eye (for example platinum) and keep it in the flame.
• making atoms: this requires energy. If you want to release atoms from the crystal lattice of the metal, you don’t always have enough energy with the flame temperature. It is often easier to make atoms from salts, we say that those salts are ‘volatile’.

Furthermore, you can only do this test in the flame with metal types that easily form atoms, these are the alkali and alkaline earth metals such as sodium, magnesium, … A number of those metals are very reactive in a pure state. Sodium, for example, starts to burn spontaneously in the air, so ‘normal metal’ is not an option there.

Kind regards