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. In addition, in this experiment we will
attempt to see emission spectra. This will be to help explain the idea of energy levels.
Materials: Metal solutions; lithium (LiNO3); strontium (Sr(NO3)2); calcium (Ca(NO3)2);
barium (Ba(NO3)2); copper (Cu(NO3)2); potassium (KNO3); sodium (NaNO3) and (NaCl);
sodium and potassium (NaNO3 + KNO3); Bunsen burner, spectroscope glasses and cobalt
glass.
Terms: Nitrate ion = NO3-1
PROCEDURE:
1.
Set up a test tube rack with 9 small to medium sized test tubes. Also get out one 250
ml beaker. Fill the beaker half-full with tap water.
2.
Wash and rinse out the test tubes with soap and water. Make sure there are no more
soap bubbles before doing the next step. Rinse the test tubes two more times with
DISTILLED WATER.
3.
Obtain 1 splint that has been soaked in each metal solution listed on your data table.
Obtain 2 splints of the sodium (NaNO3) solution, 2 splints of the potassium (KNO3)
solution and 2 splints from the sodium and potassium mixture (NaNO3 + KNO3).
4.
Place each of the different splint types in a separate labeled test tube in the test tube
rack. Be sure not to touch the soaked end of the splints, and do not allow the splints
to make contact with each other.
5.
Begin by placing an unsoaked splint in the burner flame and record the color emitted.
Use this as a reference point for the other test solutions. Read steps 6 – 9 before
beginning the rest of step 5. One at a time place the soaked end of each splint into
the burner flame and record the color emitted. One of you will look for a color other
than that produced by the plain splint, and carefully record the degree or tint of the
color detected. The other one will view the same splint using the spectroscope
glasses. You want to, as accurately as possible, identify the colors and how many are
seen in the spectrum. 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.
6.
Test all other solutions first, and then test the sodium (NaNO3) and (NaCl) solutions
last.
7.
Also test a second sodium (NaNO3) splint and record the color you see with a piece of
cobalt glass in front of your eyes.
8.
Likewise test a second potassium (KNO3) splint and record the color with the cobalt
glass in front of your eyes.
9.
Lastly, test a splint from the mixture of sodium and potassium (NaNO3 + KNO3)
solutions and record the color. Then burn the second sodium and potassium
(NaNO3 + KNO3) mixture splint and record the color you see with the cobalt glass in
front of your eyes. Record your results.
10.
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.
11.
Discard all the extinguished splints in the trashcan. Do not place splints in the sink.
Rinse out all the test tubes and the beaker, TWICE.
DATA TABLE
Metals in Solution
Flame
Color
Observation with Spectroscope
glasses
PLAIN SPLINT
Lithium (LiNO3)
Strontium (Sr(NO3)2)
Calcium (Ca(NO3)2)
Barium (Ba(NO3)2)
Potassium (KNO3)
Copper (Cu(NO3)2)
Sodium (NaNO3)
Sodium (NaCl)
Sodium (NaNO3) with Cobalt
glass
Potassium (KNO3) with Cobalt
glass
Sodium and Potassium mixture
(NaNO3 + KNO3)
Sodium and Potassium mixture
(NaNO3 + KNO3) with Co glass
UNKNOWN #1
UNKNOWN #2
QUESTIONS:
1.
Is the flame coloration a test for the metal in the solution or the nitrate ion (NO 3-1) in
the solution? How do you know?
2.
Why did I have you test solutions of both sodium nitrate (NaNO3) and sodium chloride
(NaCl)?
3.
What effect did the cobalt glass have on the observed color of the sodium and
potassium mixture?
4.
Why do you think cobalt glass is used? (Why not any other colored glass?)
5.
Which color flames are high-energy flames? Which ones are low energy flames?
6.
How sensitive would you say these flame tests are?
7.
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?
8.
What part of the metallic atom causes the color observed? Why do different kinds of
atoms give off different colors?
9.
How do the spectra compare to the flame colors observed?
10.
How do the spectra compare from one solution to another?