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Chemistry LibreTexts

Flame Colors

Chemical Concepts Demonstrated

  • Atomic emission spectra
  • Bohr atomic model

Demonstration

Different types of powdered metals and salts are sprinkled over a flame. flame (1).gif

Observations

The video shows the metals and salts in this order:

Metal or salt:

1. Copper acetate

2. Copper

3. Potassium iodide

4. Magnesium

5. Iron

6. Lithium carbonate

7. Strontium nitrate

8. Sodium chloride

Observations:

Green flame

Blue-green flame

Violet flame

White sparks

Yellow sparks

Blue flame

Red flame

Yellow flame

Explanation

When a metal or metal salt is added to a flame, a combustion reaction ensues.  This reaction excites an electron in the metal from its ground state to a higher orbital.  In order to return to its ground state, the electron releases the additional energy in the form of light. 

Different metal electrons emit different wavelengths of light to return to their respective ground states, so the flame colors are varied.  These flames can be used to produce atomic emmision spectra of the elements combusted.   Using known values of emmision spectra, one can perform a flame test on un unknown substance, gather an emmision spectrum from it, and determine which elements are in the unknown substance.

For example, in the case of copper ion, there are multiple different "paths" that the excited electrons can follow to emit photon of certain discrete energy. This produces multiple spectra lines because each discrete energy level difference will yield a specific wavelength of light, which determines the color. 

 

CuSO4.png     Cu configuration.png

Figure 1 (left): Copper is heated and as the electrons fall back, certain color of light is emitted. (right): Submicroscopic view of the electron movement, as electrons fall