Flame Tests: Spectra Of Elements
Everybody knows that a few drops of soup or milk spilled onto a gas
burner will change the blue gas flame into a mixture of colors, mostly
yellow. These colors can be used to identify the elements present
in the substance dropped into the flame. We will observe the colors
produced by several known substances. Since many elements are hard
to handle in pure form, we will use aqueous solutions of some common metals.
To isolate and observe only one element at a time, we will limit the compounds
observed to chlorides.
We will observe the following compounds: CuCl2,
LiCl, CaCl2, KCl, NaCl, BiCl3,
CsCl, SrCl2, and two unknowns.
Observe hydrogen gas in a geisler tube. What color is it?
Again observe hydrogen in the geisler tube, but this time look through
the "rainbow glasses." Draw what you see - label the colors if you
don't have colored pencils.
Adjust a Bunsen burner so it burns with a clear blue flame.
Dip the splint or nichrome wire in the solution and place it in the flame
(for convenience, we may use another method to produce the flames.
The colors should be the same regardless of method). Record your
observations about the color and appearance of the flame along with the
identity of the solution. Do not allow any of the solution to get
on the Bunsen burner. After recordingyour observations, look at the
burning solution again with the rainbow glasses on. try to draw the
line spectrum that you see, using the colored pens or pencils provided.
Repeat these steps at each station.
The last two stations are unknown salts labeled "#1" and "#2". Can
you tell which metal or metals are present in each?
How can you prove that the colors you see belong to the metal (Na, Cu,
etc.), and not chlorine or the metal chloride? Suggest an experiment.
What metal or metals were in each "unknown" solution? Explain your
Which end of the visible spectrum has the lowest energy of light (red or
The burning process produces energy that removes electrons from atoms.
As the atoms cool, the electrons join back up with the atoms, and release
energy in the form of light. Which atom(s) gave off light with the
least amount of energy?
Which atom(s) gave off light with the most amount of energy?
[Bonus: List the metals used in order from least to most reactive.]
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