Name_______________________
Period________
Chemistry Lab:
Flame Tests
When elements are heated to high temperatures, they may enter an excited state.
In a excited state, the electrons move to higher energy levels. The changes in energy that
occur when the excited electrons return to their ground state cause the substance to be
luminous or emit light. The observed colors or spectrum of the substance is caused by
the set of visible wavelengths of light emitted. Since each element emits a unique set of
wavelengths, emission spectra can be used as a tool to identify the elements.
One method used to demonstrate the emission spectrum of a substance is the
flame test. Using this method, a small amount of a substance is heated and the
characteristic glow of the substance is observed. In this experiment you will perform a
flame test on several metallic salts. Based on your observations, you will develop a
reference table which lists the flame color for each metal ion. You will then perform a
flame test on an unknown substance. By comparing your observations to the data in your
reference table, you will be able to identify the metal ion in the unknown substance.
Objectives:
In this experiment, you will
 Observe the spectra emitted from selected ions
 Identify metallic ions by the color emitted during vaporization
 Evaluate the usefulness of this method of metal identification
Equipment:
Goggles and apron
wooden splints that have been soaked in the nitrate solutions
Bunsen burner
2 cobalt glass plates
spectroscopes
Procedure:
1. Safety goggles and a lab apron must be worn for this experiment.
2. Light your Bunsen burner and adjust the flame so it is blue and hot.
3. Obtain a wooden splint soaked in calcium nitrate solution. Place the splint in the
flame. Record the color you see in the data table.
4. Look at the flame through the spectroscope. Draw the spectrum you see in the
data table. Extinguish the wooden splint.
5. Repeat steps 3 and 4 for copper nitrate, strontium nitrate, and lithium nitrate.
6. Repeat steps 3 and 4 for sodium nitrate. Then view the flame through 2 pieces of
cobalt glass. Record the color and spectrum that you see.
7. Repeat step 6 for the potassium nitrate and the sodium and potassium nitrate
mixture.
8. Using the techniques you have learned, test the unknown solution.
9. Make sure your wooden splints are completely extinguished. Then place them in
the trash can.
Analysis:
Solution
Flame Color
Spectrum
Calcium nitrate
Copper nitrate
Strontium nitrate
Lithium nitrate
Sodium nitrate
Sodium nitrate through cobalt
glass
Potassium nitrate
Potassium nitrate through
cobalt glass
Sodium nitrate & Potassium
nitrate
Sodium nitrate & Potassium
nitrate through cobalt glass
Unknown
Conclusions: Answer the following questions on a separate sheet of paper.
1. Explain how viewing the flame through the cobalt glass can make it easier to
analyze the ions being tested.
2. What metal ion would you predict to be contained in the sample of the unknown?
Why?
3. How would you characterize the flame test with respect to its sensitivity? What
difficulties could there be when identifying ions by flame test?
4. A student performed flame tests on several unknowns and observed that they all
were shades of red. What should the student do to correctly identify these
substances? Explain your answer.
5. During a flood, the labels from three bottles of chemicals were lost. The three
unlabeled bottles of white solids were known to contain the following: strontium
nitrate, ammonium carbonate, and potassium sulfate. Explain how you could
easily test the substances and relabel the three bottles. (Hint: ammonium ions do
not provide a distinctive flame color.)