Colored Flames
Introduction
The normal electron configuration of atoms or ions of an element is known as the “ground state.”
In this most stable energy state, all electrons are in the lowest energy levels available. When atoms or ions
in the “ground state” are heated to high temperatures, some electrons may absorb enough energy to allow
them to “jump” to higher energy levels. The element is then said to be in the “excited state.” This excited
configuration is unstable, and the electrons “fall” back to their normal positions of lower energy (ground
state). As the electrons return to their normal levels, the
energy that was absorbed is emitted in the form of
electromagnetic energy. Some of this energy may be in
the form of visible light. The color of this light can be
used as a means of identifying the elements involved.
Such analysis is known as a flame test.
To do a flame test on a metallic element, the
metal is first dissolved in a solution and the solution is
then held in the hot, blue flame of a Bunsen burner. This
test works well for metal ions, and was perfected by
Robert Bunsen (1811 – 1899). Many metallic ions
exhibit characteristic colors when vaporized in the burner
flame.
Purpose
The purpose is to observe the characteristic colors produced by certain metallic ions when
vaporized in a flame and then to identify an unknown metallic ion by means of its flame test.
Materials
Bunsen burner and striker Copper (II) chloride solution (CuCl2)
Inoculating loop Potassium chloride solution (KCl)
24-well well plate Barium chloride solution (Ba2Cl)
Strontium chloride solution (SrClc) Lithium chloride solution (LiCl)
Sodium chloride solution (NaCl)
Safety Considerations
As always, you should wear safety glasses when doing this experiment.
You’re working with fire here, so all fire precautions should be put in place before you start the
demonstration. Know where the fire extinguisher is in case things get out of hand.
If things do get out of hand, don’t panic!
Wash your hands thoroughly at the end of this experiment.
Procedure
1. Place several drops of each solution in the well plate according to the data sheet.
2. Light the Bunsen burner and adjust the flame so that it has a light blue cone.
3. Dip the inoculation loop into the first solution, and hold it in the flame.
4. Record the color of the flame.
5. Make sure that the loop is clean before it is dipped into the next solution.
6. Repeat steps 3 and 4 with all known solutions.
7. Test the 2 unknowns to determine their composition.
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Disposal and Cleanup
Rinse the metal solutions down the drain with plenty of water.
Wash your hands before leaving lab.
Questions
1. State at least three problems that may be involved when using flame tests for
identification purposes.
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2. Which ions produce similar colors in the flame tests?
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3. Explain how the colors observed in the flame tests are produced.
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4. Why is it necessary to carefully clean the wire before testing each solution?
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5. In each solution there was also an anion. Why did we not see a color from the
anion?
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6. Some commercially available fireplace logs burn with a red and/or green flame.
On the basis of your data, what elements could be responsible for these colored
flames?
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7. Aerial fireworks contain gunpowder and chemicals that produce colors. What
elements would you include to produce the following colors?
a. crimson red
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b. yellow
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