CHEMISTRY
Flame Tests
Problem
Can we identify an unknown mixture by using a flame test?
Introduction
Flame tests provide a way to qualitatively test for the presence of specific metallic ions. The
heat of the flame excites the electrons in the metal ion, and this energy is released as the
electrons “fall back” to their ground states. The color we see is a combination of the visible
wavelengths of light emitted by the ion.
In this lab you will perform flame tests on seven different metal ions. You will use your
observations to identify two unknown solutions.
Materials
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Safety goggles
Lab apron
Nichrome wire loop
Well plate with solutions
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Bunsen burner
Wash bottle with deionized water
6.0 M HCl
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potassium chloride
sodium chloride
strontium chloride
Solutions of the following salts:
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calcium chloride
copper(II) chloride
lithium chloride
Safety
1. Safety goggles and a lab apron must be worn at all times in the laboratory.
2. Many of these salts are toxic. If you come in contact with any solution, wash the contacted
area thoroughly.
3. The 6.0 M HCl is corrosive. Handle it with extreme care.
Procedure
1. Clean the nichrome wire. First, rinse with deionized water. Next, dip the loop into the 6.0 M
HCl solution. Place the loop into the flame of the Bunsen burner for about a minute. Pay
attention to the color of the clean nichrome wire in the flame.
2. Place a small amount of each solution in separate wells in the well plate.
3. Perform a flame test on each solution by first heating the loop of the nichrome wire in the
Bunsen burner. Hold the watch glass with the solution to be tested next to the intake of the
Bunsen burner and place the hot loop into the solution. Make careful observations of the flame
of the Bunsen burner and record your observations.
4. Clean the wire as described in step 1, and test each of the remaining six solutions separately.
5. Obtain two unknown solutions from your teacher and perform flame tests on each (cleaning
the wire between unknowns). Record all observations.
Data/Observations
Salt solution
Observation
calcium chloride
copper(II) chloride
lithium chloride
potassium chloride
sodium chloride
strontium chloride
Unknown #1
Unknown #2
Analysis and Conclusions
1. How does the flame test provide support for quantized energy levels? Explain your answer.
2. List the metal ions present in your two unknown solutions and provide reasons.
Name___________________________
Report for Experiment 47
Section___________ Date___________
Flame Tests
Prelaboratory Assignment
1. Why must the nichrome wire be cleaned thoroughly after each flame test?
2. Why do we see colors in the flame tests, and why are there different colors for different metal
ions?
Data/Observations
Salt solution
Observation
calcium nitrate
copper(II) nitrate
lithium nitrate
potassium nitrate
sodium chloride
strontium nitrate
Analysis and Conclusions
1. How does the flame test provide support for quantized energy levels? Explain your answer.
2. Fill in the table below.
Unknown #
1
2
Observations
Metal ions present
Reason
Experiment 47
Flame Tests
Introduction
Intent
This is a short, colorful experiment in which students observe visual evidence for the concept of
quantized energy levels in atoms.
Objectives
1. To observe the flame colors produced by various metal ions in solution.
2. To use flame tests to identify ions in solutions.
Materials (for each lab team of 2 students)
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Safety goggles (2)
Lab apron (2)
Nichrome wire loop
Well plate with solutions
Bunsen burner
Wash bottle with deionized water
6.0 M HCl
Seven watch glasses (or petri dishes)
Solutions (0.10 M) of the following salts:
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barium nitrate
calcium nitrate
copper(II) nitrate
lithium nitrate
potassium nitrate
sodium chloride
strontium nitrate
Preparation Hints
Place a set of small containers of the known ion solutions at each lab station. This will make it
easier and less time consuming for the students.
To prepare the 0.1 M salt solutions:
Ba(NO3)2, 26.13 g Ba(NO3)2/liter
Ca(NO3)2, 23.6 g CaNO3 · 4H2O/liter
Cu(NO3)2, 24.2 g Cu(NO3)2 · 3H2O/liter
LiNO3, 6.89 g LiNO3/liter
KNO3, 10.1 g KNO3/liter
NaCl, 5.84 g NaCl/liter
Sr(NO3)2, 21.16 g Sr(NO3)2/liter
6.0 M HCl, Add equal volumes of concentrated acid and water
If you plan to use well plates be sure they are the ceramic type. Plastic well plates will melt if
touched by hot nichrome wire.
Prelaboratory Discussion
Students must make careful observations in this experiment. The colors do not remain in the
flame for long. It is important for the students to recognize the color of the HCl on the nichrome
wire. This color can obscure the color of the metal ion.
Tell the students that 6.0 M HCl is corrosive. They should handle it with extreme care. If they
come in contact with any solution, they need to wash the contacted area thoroughly. Make sure
they know the locations of eye-washes.
Students should tie back their hair and loose clothing whenever they work with a flame in the
lab. Students will often deposit matches in the sink. Let them know to dispose of burned
matches in the trashcan after they are cool.
Procedure Hints
1. As you circulate from group to group look for multiple colors in the flames.
2. The flame from the Bunsen burner must be blue, not yellow.
Disposal
1. Dispose of all solutions according to local regulations.
2. Have the final class performing the experiment clean the nichrome wires thoroughly with the
HCl. Store them for later use.
Name___________________________
Report for Experiment 47
Section___________ Date___________
Flame Tests
Prelaboratory Assignment
1. Why must the nichrome wire be cleaned thoroughly after each flame test?
The wire must be cleaned to keep cross contamination of solutions from occurring.
2. Why do we see colors in the flame tests, and why are there different colors for different metal
ions?
Heat from the flame causes the ions to absorb energy exciting their electrons. When the
electron returns to its ground state, this excess energy is released in the form of light. This light
is visible with specific wavelengths for particular ions (thus characteristics colors are emitted).
Data/Observations
Salt solution
Observations
barium nitrate
The flame is green.
calcium nitrate
The flame is brick-red.
copper(II) nitrate
The flame is green.
lithium nitrate
The flame is deep red.
potassium nitrate
The flame is violet.
sodium chloride
The flame is yellow/orange.
strontium nitrate
The flame is orange red.
Analysis and Conclusions
1. How does the flame test provide support for quantized energy levels? Explain your answer.
The light comes from the excited atoms releasing energy as visible light. Because we see
colors, this light must be of only certain wavelengths (if it consisted of all wavelengths, the light
would be “white”). Since only certain amounts of energy are released, the energy levels must be
quantized.
2. Fill in the table below:
Answers will vary depending on unknowns.
Unknown #
Observations
Metal ions present
Reason
1
2
Something Extra
Does the anion in a salt affect the color observed in a flame test? Design an experiment to
answer this question, discuss it with your teacher, and try it.
The anion will not affect the observations.