Flame Tests – Non formal lab
Introduction
According to the Bohr theory of the atom, electrons may occupy only specific energy levels. When an
atom absorbs sufficient energy, an electron can "jump" to a higher energy level. Higher energy levels tend
to be less stable, however, and if a lower energy level is available, the electron will "fall back", giving off
energy in the process. The difference in energies between the two levels is emitted in the form of
electromagnetic radiation. If the wavelength of the released photon is between 400 and 700 nm, the
energy is emitted as visible light. The color of the light depends on the specific energy change that is
taking place.
White light is a continuous spectrum in which all the wavelengths of visible light are present. An
excited atom, however, produces one or more specific lines in its spectrum, corresponding to the specific
changes in energy levels of its electrons. Because each element has a distinct electron configuration, each
has a unique line spectrum.
Flame tests are a quick method of producing the characteristic colors of metallic ions (we will talk
more about ions later). The loosely held electrons of a metal are easily excited in the flame of a lab
burner. The emission of energy in the visible portion of the spectrum as those electrons return to lower
energy levels produces a colored flame. The color is a combination of the wavelengths of each transition,
and may be used to determine the identity of the metal.
In this investigation you will perform flame tests on seven metallic ions, and use your results to determine
the identity of three unknowns.
Safety Precautions: Goggles, apron, closed toe shoes, hair tied back. Use appropriate safety with
open flame (burner).
Purpose: Determine what color flame is associated with specific metallic ions
Identify the metallic ions in three unknown salts using a flame test
Pre-Lab Question
1. What does a flame test indicate about the energy changes taking place among the electrons in a
metallic ion?
2. What wavelengths correspond to the visible spectrum? Which color has the shortest wavelength?
The longest?
Materials
Goggles
Non-plastic cotton swabs (Q-tips)
3 unknowns
lab burner
7 known ionic salts
Apron
deionized water
striker
* Group responsibility: Each lab group will bring at least 12 non-plastic cotton swabs (Q-tips)
Procedure
1. You will find all the ionic salts and unknown on your teacher assigned lab table/cart.
2. Set up and light the lab burner. You should have to do this only once.
3. For each test, dip the end of the swab in the deionized water, then dip it in one of the salts, and
hold it in the flame. Observe the color that is given off and record these observations.
4. Obtain samples from three unknown salts, I, II, and III . . . and predict the metal ions present in
each salt (We know they all look the same. That's why we need a flame test to find out the actual
metal ions present!) Hint: Each unknown is a mixture of two salts.
5. Repeat step 3 and record observations of the colors emitted.
DATA
Salt
Chemical
Formula
Chemical Name
Color (observations)
A
B
C
D
E
F
G
Unknown
Predicted Metal
Ions
Color (observations)
I
II
III
Answer the following sections * in complete sentences: ON A SEPARATE SHEET OF PAPER.
*Post Lab Questions:.
1.
2.
3.
4.
5.
6.
7.
8.
What metallic ions are present in the unknown solutions, I, II, and III?
What is the reason for all the salts in your test being chlorides?
Summarize the process that causes the colors that are seen in a flame test.
What is the relationship between the colors you saw and the lines of the electromagnetic spectrum
produced by the metals?
When a glass rod is heated, a yellow flame is observed around the point of heating. What does the
yellow flame indicate? Why is it observed when glass is heated?
What other equipment could you use in this investigation if burners were not available?
How are metallic salts used in fireworks?
Explain what kind of data did you collect today?
*Conclusion: Always respond to the purpose by using your data
*ESOE: Give at least two possible sources of error (*do not forget to explain the significance of the
error(s) based on your data