FLAME TESTS
PURPOSE: The purpose of this experiment is to determine the characteristic color emitted by
burning solutions of different metals in a burner flame.
MATERIALS: Metal solutions, Bunsen burner and cobalt glass.
TERMS: Nitrate ion == NO3 –1
PROCEDURE:
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Set up a test tube rack with 6 small test tubes. Also get out two 150 ml. beakers and
two 250 ml. beakers. Fill one 250 ml beaker half-full with tap water.
Rinse out all the test tubes and beakers with distilled water TWICE.
Obtain 1 splint that has been soaked in each metal solution listed on your data table.
Also obtain 2 splints of the sodium (NaNO3) solution, 2 splints of the potassium
(KNO3) solutions and two splints of the sodium & potassium mixture.
Place each different splint type in a separate test tube in the test tube rack and in each
of the three beakers. Be sure to label the test tubes and beakers so you can identify
what solutions the splints came from. BE SURE NOT TO TOUCH THE SOAKED
END OF THE SPLINTS, AND DO NOT ALLOW THE SPLINTS TO MAKE
CONTACT WITH EACH OTHER.
Begin by placing an “unsoaked” splint in the burn flame and record the color emitted.
Use this as a reference point for the other test solutions. One at a time place the
soaked end of each splint into the burner flame and record the color emitted. Look
for a color other than that produced by the plain splint, and carefully record the
degree or tint of the color detected. If necessary, test a second splint to detect the
correct color. The color may not persist long. After you have determined the color
emitted, extinguish the splint by placing it in the beaker with the tap water.
Test all other solutions first, and then test the sodium (NaNO3) and (NaCl) solutions
last.
Also test a second sodium (NaNO3) splint and record the color you see with a piece of
cobalt glass in front of your eyes.
Likewise test a second potassium (KNO3) splint and record the color with the cobalt
glass in front of your eyes.
Lastly test a splint from the mixture of sodium (NaNO3) and potassium (KNO3)
solutions and record the color. Then burn the second sodium and potassium mixture
splint and record the color you see with cobalt glass in front of your eyes. Record
your results.
Obtain and test two unknown solutions. Record the number of the unknown, the
color emitted and the metal solution you think is in the unknown.
Discard all the extinguished splints in the trash can. Do not place splints in the sink.
Rinse out all test tubes and beakers TWICE.
QUESTIONS—Complete sentences, please!
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Is the flame coloration a test for the metal in the solution or the nitrate ion (NO3-) in
the solution? How do you know?
How did the results of the sodium nitrate (NaNO3) and sodium chloride (NaCl)
compare? Why did I have you test solutions of both sodium nitrate (NaNO3) and
sodium chloride (NaCl)?
What part of the metallic atom causes the color observed? Why do different kinds of
atoms give off different colors?
Can you think of a practical example of this lab that is evident each summer in cities
across the US?
What effect did the cobalt glass have on the observed color of the sodium and
potassium mixture?
Why do you think cobalt glass is used? Why not some other colored glass?
Which metal flames are high-energy flames? Which metals are low energy flames?
How sensitive would you say these flame tests are? In other words, does the wood
stick require lots of the metal atoms in order to produce the color? Explain your
answer.
If you were trying to use these flame tests to determine if any of these metals were
dissolved in your drinking water, what possible difficulties would you encounter?
DATA TABLE
METAL IN SOLUTION
FLAME COLOR
PLAIN
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Lithium (LiNO3)
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Strontium (Sr(NO3)2)
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Calcium (Ca(NO3)2)
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Barium (Ba(NO3)2)
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Potassium (KNO3)
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Copper (Cu(NO3)2)
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Sodium (NaNO3)
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Sodium (NaCl)
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Sodium & Potassium Mixture
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Sodium (NaNO3) with Co glass
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Potassium (KNO3) with Co glass
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Sodium & Potassium Mixture with Co glass
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Unknown # _____
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Unknown # _____
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