LAB: Emission Spectroscopy
(aka Flame Tests)
Name
Date________ Block___
Purpose: 1. To observe and compare continuous and bright-line spectra.
2. To identify an unknown metal ion by means of a flame test.
Materials/Equipment
For Parts I and II:
student-grade diffraction grating
low wattage incandescent light source
fluorescent light source
spectrum gas tubes for different elements
high-voltage power source for gas tubes
For Part III:
lab apron and safety goggles
Bunsen burner/matches
labeled set of solids:
BaCl2, CaCl2, LiCl, CuCl2, KCl, NaCl, SrCl2
DI H2O in wash bottle
50-mL beaker
nichrome wires with loops at one end
crucible tongs
student-grade diffraction grating or glasses
NOTE:
A diffraction grating separates the light that passes through it into distinct lines of color.
Each colored line is produced by photons of visible light having the same frequency and
wavelength and therefore the same energy.
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Flame Test Lab: pre-lab questions,
data and observations, analysis
and conclusions
Name____________________________
Date_________
Block____
Pre-Lab Questions
1. According to the quantum theory of the atom, where may the electrons of an atom be
found?
2. What is meant by the “ground state” of an atom?
______________________________________________________________________
3. Explain how electrons can become “excited.”
4. Write the mathematical equation that is used to determine the energy content of a
packet of light that has a specific frequency. (It is in your textbook.)
___________________________
5. When excited electrons return to the ground state, what form of energy is usually
emitted?
___________________________
6. How should the flame of the Bunsen burner be adjusted so that the only light color
observed is that being emitted from the atoms of the salts used in this lab? What would
you observe if you did NOT make this adjustment?
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Procedure
Part I.
1. Using the diffraction grating, observe the spectrum emitted by a low wattage
incandescent light source. Record your observations in the appropriate data table
provided.
2. Now aim the diffraction grating at a fluorescent light source. Record your
observations in the appropriate data table provided.
Part II.
The high-voltage power source required for the spectral gas tubes will be set up
for the class. This will be done by the teacher only; do NOT touch either the gas
tubes or the power source.
1. Once a gas tube has been inserted into the power source and the power source has
been turned on, aim the diffraction grating at the glowing tube. Record the order of
positions (from left to right as you view the emission spectrum) of the bright emission
lines from that gas in the table provided.
2. Repeat for the other gas tubes.
Part III.
1. Carefully and correctly ignite the Bunsen burner. Do not dispose of the matches in
the sinks – place used matches in the small glass jars on your lab bench. Adjust
the flame so it is a pale blue from its base to the tip of the flame. The height of the
flame should be no higher than the width of your hand.
2. Select one of the known solids. Holding the nichrome wire with crucible tongs, wet
the looped end of the nichrome wire with DI water and then dip the loop into the
solid.
3. Hold the loop with the solid at the side of the pale blue flame of the burner. Observe
the color of the flame and record your observations in the table for Part II labeled
Observations of Flame Colors.
Repeat for the remaining known solids.
3. OPTIONAL: While your partner uses the spectroscope or diffraction grating to view
the flame, repeat Step 2. Record your observations in the table labeled Emission
Spectra of the 7 Metal Ions. Once your partner has completed his/her observations,
switch places. When you have both finished your observations, turn off the Bunsen
burner at the gas jet and disconnect the hose.
4. Be sure to keep your lab bench clean. Wipe up any spills immediately.
Wash your hands thoroughly with soap and water before leaving the lab.
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DATA and OBSERVATIONS
Part I. Results of viewing two different sources of continuous spectra.
Incandescent spectrum (write the initials of the visible light colors you see in the
order in which you observe them)
Fluorescent spectrum (write the initials of the visible light colors you see in the
order in which you observe them)
Part II. Results of observing spectra from excited gases. Place a check mark
in the box for each color of visible light that you observe in each spectrum.
GAS TUBE
(element
symbol)
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RED
ORANGE
YELLOW
GREEN
BLUE
VIOLET
Part III. Results of flame tests on known substances. Note: the flame colors are
from the positive ion (the first element in each compound), not from the chloride
ion. NOTE: for KCl, observe the flame through the cobalt glass (dark blue
glass) to eliminate the yellow flame color due to the presence of sodium.
Observations of Flame Colors
Substance
Observations
BaCl2
CaCl2
CuCl2
LiCl
NaCl
KCl
SrCl2
OPTIONAL: View the flame of each solid with the diffraction glasses.
Emission Spectra of the 7 Metal Ions (Place a check in the box for each color of
visible light that you observe.)
Metal Ion
RED
ORANGE
YELLOW
GREEN
BLUE
VIOLET
Ba+2
Ca2+
Cu2+
Li+
Na+
K+
Sr+
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ANALYSIS and CONCLUSIONS
1. Compare the spectra produced by the incandescent and fluorescent light
sources.
2. Explain why some spectral lines are brighter than others.
3. Why is it possible to identify an element on the basis of its emission
spectrum?
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