When burning a salt, how do we know the flame color comes from the metal ion and not the non-metal ion? I did a lab on this by burning different salts and observing the different flame colours. This was one of the analyze questions.   Your help will be very much appreciated!

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When you are doing a flame test you are using a solution of positive metal cations and negative metal anions.  The reason a color is observed is that during the flame test the positive ion can reacquire an electron, becoming a neutral element again. The electron that is gained is in a higher energy level and when it drops to a lower energy level a photon of light is emittted. The wavelength of the light emitted determines the color.

Since anions already have an extra electron, they would have to gain even more energy so the electron could then drop to a lower energy level so a photon could be emitted.  As this does not happen, the anion does not generate a color.

You could also test this by using the same metal ion with a variety of different anions and see that the same color is produced in each case.

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