Name: ______________________________________ Date: _______ Period: ____
Flame Test
Introduction:
When atoms or ions in the ground state are heated to
high temperatures, some electrons may absorb enough
energy to allow them to “jump” to higher energy levels.
These excited state electrons are unstable and they will
“fall” back to their normal positions of lower energy.
As the electrons return to the ground state, the energy
that was absorbed is emitted in the form of
electromagnetic energy. Some of this energy may be in
the form of visible light.
When electrons become excited, the flame will only
produce color for a few seconds at most. Many elements
produce flames of a characteristic color when they come in contact with the flame of the burner.
Using this method, scientists can determine some elements in an unknown mixture or solution.
A flame test is made by taking a wooden splint soaked in a chemical of the known element, heating
it in a flame, and noting the distinctive color of the flame produced by the vaporized salt.
Important vocabulary in this lab includes:
•
Excited State - when an electron gains enough energy to temporarily leave its ground state
orbital and move to an orbital of higher energy.
•
Ground State - the level of energy that an electron will be in when it is not excited.
Objective:
To observe the characteristic colors produced by metallic ions when heated in a flame, and to
identify an unknown ionic compound by means of its flame test.
Materials and Equipment:
o
o
o
o
8 Wooden splints soaked in Ionic Solution (NaCl, KCl, LiCl, CaCl2, CrCl2, CuCl2, BaCl2, NiCl2)
1 Wooden splint with unknown
Bunsen burner
Waste Beaker
Procedure:
1. Obtain 8 wooden splints that have been soaking in the metal salt solutions. Be sure to label each wooden
splint with the names of the salts so they are not mixed up.
2. Light the Bunsen burner. Be sure to avoid a yellow flame.
Name: ______________________________________ Date: _______ Period: ____
3. Carefully place the end of the wooden splint that was soaked in the metal salt solution at the top of the
inner blue flame. Record the color and intensity (bright/faint) of the flame in the data table. The color
given off by the salt is the initial color observed, not the yellow-orange color produced by the burning
wood.
• Use your iPad to record each test to aid in your analysis and for discussions in class.
4. Repeat with the other 7 salts. Be sure to record the colors as precisely as possible.
5. If more observations are needed, tell me for additional resources. Otherwise, discard the wooden splints
at the end of the experiment.
Data:
Ionic Compound
LiCl
Metal Ion
Color in
Flame
Wavelength
(nm)
Wavelength
(m)
Energy (J)
KCl
CoCl2
CaCl2
CrCl2
CuCl2
BaCl2
NiCl2
Unknown
Calculations:
In order to calculate the amount of energy found in emitted photon of light, seen as the
color of light you observed you will need to use the following equation.
Δ𝐸𝐸 =
𝑐𝑐 ∗ ℎ
𝜆𝜆
c: Speed of Light - 3x108 m/s
h: Planck's Constant - 6.626x10-34 J*s
λ: wavelength - from observation in mm
• Remember you will need to use the conversion 1m = 1x109nm
Name: ______________________________________ Date: _______ Period: ____
Questions:
1. What inaccuracies may be involved in using flame tests for identification purposes?
The electromagnetic spectrum is shown below. Recall that energy is proportional to frequency, while
frequency is inversely proportional to wavelength. Use this information to answer questions 2-5 below.
2. List the colors observed in this lab from the highest energy to the lowest energy.
3. List the colors observed in this lab from the highest frequency to the lowest frequency.
4. List the colors observed in this lab from the shortest wavelength to the longest wavelength.
5. What is the relationship between energy, frequency, and wavelength?
Name: ______________________________________ Date: _______ Period: ____
6. Based on the results of your experiment, what metal was found in the unknown? Explain your
reasoning.
7. Do you think we can use the flame test to determine the identity of multiple unknowns within a
mixture? Why or why not?
8. How are electrons “excited” in this part of the experiment? What does it mean when the
electrons are “excited”?
9. Why do different chemicals emit different colors of light?
10. In this lab, you observed that each element emits a unique color of light when heated in a flame.
If these light emissions were examined through a prism, you would observe that the emitted
light is actually composed of different wavelengths of light that may lie in the violet region, the
green region, or the red region of the visible spectrum. Each element has a unique emission
spectrum. Research how scientists apply these emission spectra to investigate the chemical
composition of stars? What is the emission spectrum of the sun and what does this spectrum
reveal about the types of elements in the sun?