Honors Chemistry
Name: _______________________________
Period: _____
Lab Partners: ________________________________________________
Flame Test Experiment
Introduction:
When elements are heated to high temperatures, some of the electrons in the atoms
absorb the heat energy and jump to higher energy orbitals. We say they are excited. Eventually
these excited electrons lose their extra energy and fall back to lower energy orbitals. The energy
lost by the electron shoots out of the atom in small packages of light, called photons. For
metals, these photons have energies in the visible region of the electromagnetic spectrum, which
means that humans can see it. We can even tell one energy from another, by the color. Red
light, for example, is less energetic than orange or yellow and so on. In fact, the acronym
ROYGBIV gives us the colors of visible light in order from least energetic to most. (Red,
Orange, Yellow, Green, Blue, Indigo, Violet)
Each element gives off a distinct (unique) pattern of energy when its electrons are
excited. The pattern corresponds to the energy changes that the electrons of that particular
element can make as they go from one orbital to another orbital. The pattern is constant for a
particular element, because the element always has the same ground state electron
configuration. Once the pattern, called a spectrum, of an element is known it can be used to
identify the element. Astronomers, for example, analyze the light coming from stars. Once they
find the spectra of this light, they can match these spectra with the spectra of elements to see
which elements are in that star. (Pretty neat, huh!) Crime scene detectives can take evidence
back to a laboratory where it can be analyzed this way too. Very sophisticated devices, called
flame spectrometers do most of the work for the technician. In this lab, you will be the
technician, but you will use a simple flame and your eyesight as your flame spectrometer.
Purpose:
The purpose of this lab is twofold:
(1) to see the colors that are emitted by various metal ions and
(2) to see how flame tests can be used to identify metals.
Pre-Lab Questions:
1.
2.
3.
4.
Define the seven terms that are written in bold type in the “Introduction and Procedure” sections
of this lab.
Does the cation or the anion provide the different colors in this experiment?
Which color of the spectrum has the most energy and which has the least?
What would happen if you did not clean the nichrome wire between tests?
Flame Test Lab
Safety:
1. Wear safety glasses and lab apron.
2. Tie back loose hair.
3. Never leave an open flame unattended.
4. Ensure that the gas lines are firmly connected to the Bunsen burner and the gas outlet.
5. Be sure all flammables are fully extinguished before disposal.
Procedure:
1. Put on lab apron and safety goggles.
2. Label each of the test tubes with one of the following compounds: LiCl, CaCl2, KCl,
CuCl2, SrCl2, NaCl, BaCl2, CoCl2, and unknown.
Names of the aqueous solutions:
Chemical Symbol
Name
LiCl
Lithium Chloride
CaCl2
Calcium Chloride
KCl
Potassium Chloride
CuCl2
Copper (II) Chloride
SrCl2
Strontium Chloride
NaCl
Sodium Chloride
BaCl2
Barium Chloride
CoCl2
Cobalt Chloride
3. Add 5 mL of each solutions of a metal salt to a different clean test tube.
4. Light the Bunsen burner with the sparker provided. Make sure the flame is blue. You
may need to adjust the amount of air or the amount of gas.
5. Clean the nichrome wire loop by dipping it into the hydrochloric acid (HCl) and then into
the distilled water and heat the wire in the hottest part of the flame until no color shows.
6. When the nichrome wire loop is clean, dip the wire in the test tube containing an
aqueous solution of a metal salt (a metal cation and a chloride/nitrate anion). Hold it in
the hottest part of the flame. Record your observation of the color of the flame on the
data table. The color will only last a few seconds; record the first color you see in the
flame and repeat at least once to ensure you can identify the color.
7. Repeat the process of cleaning the nichrome wire. Now get ready to test another solution.
8. Test all of the solutions and make sure that you record the color of the flame for each
element on the Data Table.
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Flame Test Lab
9. Check your flame colors to known results. The teacher will provide the colors for the
known results.
10. Once your data table is complete, you are ready to test an unknown. Obtain a sample of
unknown solution from the teacher. Perform the flame test on the unknown. Record the
color and match the color to one of the metals in the experiment. Write the identity of the
unknown on your lab paper.
11. Before leaving the laboratory, wash your hands thoroughly with soap and water.
Data:
Metal Cation
Color of Flame
Results:
Unknown # _______ Unknown Color ___________
Unknown Identity: _________
Conclusion Questions:
1.
Why is light emitted by elements when they are heated?
2.
How is this light useful to scientists?
3.
Do you think a flame test could be used to identify the metals present in a mixture? Explain.
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Flame Test Lab
4.
What would be observed if the light emitted in the flame tests were passed through a prism?
5.
Aerial fireworks contain gunpowder and chemicals that produce colors. What elements would
you include to produce the following colors? A) crimson red B) yellow C) green
6.
Write the full electron configurations for each of the metal cations.
7.
List the metallic elements used in the flame tests in order of increasing energy (frequency) of
light emitted.
Bonus:
What is the relationship between the energy of light emitted and the position of the
element in the periodic table?
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Revised: 25 Oct 2011