Catalog No. AP5607
Publication No. 5607
Flame Test Kit
Student Laboratory Kit
Introduction
Just as a fingerprint is unique to each person, the color of light emitted by metals heated in a flame is unique to each metal.
In this laboratory activity, the characteristic color of light emitted for calcium, copper, lithium, potassium, sodium, and strontium
will be observed.
Chemical Concepts
• Flame Tests
• Absorption/Emission
Background
Absorption and Emission of Light in a Flame
In Equation 1,
Excited Energy State
Absorption of Energy
An electron may relax all the way back down to the ground state in a
single step, emitting a photon in the process. Or, an electron may relax back
down to the ground state in a series of smaller steps, emitting a photon with
each step. In either case, the energy of each emitted photon is equal to the
difference in energy between the excited state and the state to which the
electron relaxes. The energy of the emitted photon determines the color of
light observed in the flame. Because colors of light are commonly referred to
in terms of their wavelength, equation 1 is used to convert the energy of the
emitted photon to its wavelength.
ΔE = hc
Equation 1
λ
Increasing Energy
When a substance is heated in a flame, the substance’s electrons absorb energy from the flame. This absorbed energy allows
the electrons to be promoted to excited energy levels. From these excited energy levels, the electrons naturally want to make a
transition, or relax, back down to the ground state. When an electron makes a transition from a higher energy level to a lower
energy level, a particle of light called a photon is emitted. A photon is commonly represented by a squiggly line (see Figure 1).
Emission of Light
Ground State
Figure 1. Absorption and Emission of Light.
ΔE is the difference in energy between the two energy levels in Joules,
h is Plank’s constant (h = 6.626 × 10–34 Jsec),
c is the speed of light (c = 2.998 × 108 m/sec), and
λ is the wavelength of light in meters.
Wavelengths are commonly listed in units of nanometers (1 m = 1 × 109 nm), so a conversion between meters and nanometers is
generally made.
The color of light observed when a substance is heated in a flame varies from substance to substance. Because each element
has a different electronic configuration, the electronic transitions for a given substance are unique. Therefore, the difference in
energy between energy levels, the exact energy of the emitted photon, and its corresponding wavelength and color are unique to
each substance. As a result, the color observed when a substance is heated in a flame can be used as a means of identification.
The Visible Portion of the Electromagnetic Spectrum
Visible light is a form of electromagnetic radiation. Other familiar forms of electromagnetic radiation include γ-rays such as
those from radioactive materials and from space, X-rays which are used to detect bones and teeth, ultraviolet (UV) radiation from
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IN5607
062007
the sun, infrared (IR) radiation which is given off in the form of heat, the microwaves used in radar signals and microwave ovens,
and radio waves used for radio and television communication. Together, all forms of electromagnetic radiation make up the electromagnetic spectrum (see Figure 2). The visible portion of the electromagnetic spectrum is the only portion that can be detected
by the human eye—all other forms of electromagnetic radiation are invisible to the human eye.
Higher Energy
Lower Energy
γ−Rays
10–16
10–14
X-Rays
10–12
10–10
UV
10–8
IR
Radio waves
FM
AM
Microwaves
10–6
10–4
10–2
100
Orange
Red
102
Long Radio Waves
104
106
108
λ (m)
Visible spectrum
Violet
Blue
400
Green
Yellow
500
600
700
Wavelength, λ (nm)
Figure 2. The Electromagnetic Spectrum.
The visible portion of the electromagnetic spectrum is only a small part of the entire spectrum. It spans the wavelength region
from about 400 to 700 nm. Light of 400 nm is seen as violet and light of 700 nm is seen as red. According to equation 1, wavelength is inversely proportional to energy. Therefore, violet light (400 nm) is higher energy light than red light (700 nm). The color
of light observed by the human eye varies from red to violet according to the familiar mnemonic ROY G BIV: red, orange, yellow,
green, blue, indigo, and violet. As the color of light changes, so does the amount of energy it possesses.
Table 1 lists the wavelengths associated with each of the colors in the visible spectrum. The representative wavelengths are
used as a benchmark for each color. For example, instead of referring to green as light in the wavelength range 500–560 nm, one
may simply refer to green light as 520 nm light.
Representative Wavelength, nm
Wavelength Region, nm
Color
410
400–425
Violet
470
425–480
Blue
490
480–500
Blue-green
520
500–560
Green
565
560–580
Yellow-green
580
580–585
Yellow
600
585–650
Orange
650
650–700
Red
Table 1.
Materials
Chemicals
Equipment
Calcium chloride, CaCl22H2O, 1–1.5 g
Beakers, 250-mL, 2
Cupric chloride, CuCl22H2O, 1–1.5 g
Laboratory burner
Lithium chloride, LiCl, 1–1.5 g
Watch glasses or weighing dishes, 6
Potassium chloride, KCl, 1–1.5 g
Wooden splints soaked in water, 6
Sodium chloride, NaCl, 1–1.5 g
Strontium chloride, SrCl26H2O, 1–1.5 g
Water, distilled or deionized, 250 mL
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IN5607
© 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Flame Test Kit, Catalog No. AP5607, from Flinn Scientific, Inc.
No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and
retrieval system, without permission in writing from Flinn Scientific, Inc.
Safety Precautions
Cupric chloride is highly toxic by ingestion; avoid contact with eyes, skin, and mucous membranes. Lithium chloride is moderately toxic by ingestion and is a body tissue irritant. Fully extinguish the wooden splints by immersing them in a beaker of water
before discarding them in the trash to avoid trashcan fires. Wear chemical splash goggles, chemical-resistant gloves, and a chemicalresistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.
Procedure
1. Fill a 250-mL beaker about half-full with distilled or deionized water. Obtain six wooden splints that have been soaked in
distilled or deionized water. Place them in this beaker of water to continue soaking at your lab station.
2. Fill a second 250-mL beaker about half-full with tap water. Label this beaker “rinse water”.
3. Label six watchglasses (or weighing dishes) “CaCl2”, “CuCl2”, “LiCl”, “NaCl”, “KCl”, “SrCl2”. Place a small scoopful
(about 1–1.5 g) of each metallic solid in the corresponding watchglass (or weighing dish).
4. Light the laboratory burner.
5. Dip the soaked end of one of the wooden splints in one of the metallic salts, then place it in the flame. Observe the color of
the flame. Allow the splint to burn until the color fades. Try not to allow any of the solid to fall into the barrel of the laboratory burner. If necessary, repeat the test with the same splint and salt.
6. Immerse the wooden splint in the “rinse water” to fully extinguish it, then discard it in the trash.
7. Record your observations for the flame color produced by the metallic salt in the Data Table.
8. Repeat Steps 5–7 for the other five metallic salts. Record your observations for the flame color produced by each metallic
salt in the Data Table.
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IN5607
© 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Flame Test Kit, Catalog No. AP5607, from Flinn Scientific, Inc.
No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and
retrieval system, without permission in writing from Flinn Scientific, Inc.
Name: ___________________________________
Data Table 1
Metal
Color of Flame
Data Table 2
Metal/Color of Flame
λ (nm)
λ (m)
ΔE (J)
Post-Lab Questions
1. Use Table 1 in the Background section to record the approximate wavelength of light emitted for each metal in Data Table 2.
2. Convert each of the wavelengths in the Data Table from nanometers to meters. Record the wavelengths in meters in the
Data Analysis Table. Show at least one sample calculation in the space below.
3. Use Equation 1 from the Background section to calculate the change in energy, ΔE, for each metal. Show all work. Record
the values in Joules in Data Table 2.
4. Predict the color of the flame if the following materials were heated in the flame. Explain your predictions.
a. Cupric nitrate, Cu(NO3)2
b. Sodium sulfate, Na2SO4
c. Potassium nitrate, KNO3
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IN5607
© 2007 Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted only to science teachers who have purchased Flame Test Kit, Catalog No. AP5607, from Flinn Scientific, Inc.
No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and
retrieval system, without permission in writing from Flinn Scientific, Inc.
Teacher’s Notes
Flame Test Kit
Materials Included in Kit
Calcium chloride, CaCl22H2O, 50 g
Sodium chloride, NaCl, 50 g
Cupric chloride, CuCl22H2O, 50 g
Strontium chloride, SrCl26H2O, 50 g
Lithium chloride, LiCl, 50 g
Wooden splints, pkg/100
Potassium chloride, KCl, 50 g
Additional Materials Needed (for each lab group)
Beakers, 250-mL, 2
Watch glasses or weighing dishes, 6
Laboratory burner
Water, distilled or deionized, 250-mL
Safety Precautions
Cupric chloride is highly toxic by ingestion; avoid contact with eyes, skin, and mucous membranes. Lithium chloride is moderately toxic by ingestion and is a body tissue irritant. Fully extinguish the wooden splints by immersing them in a beaker of water
before discarding them in the trash to avoid trashcan fires. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Please review current Material Safety Data Sheets for additional safety, handling, and disposal information.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures governing the disposal of laboratory waste. Remaining amounts of the metallic salts included in this kit may be saved and reused or disposed of in the trash according to Flinn Suggested Disposal Method #26a.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Evidence, models, and explanation
Content Standards: Grades 5–8
Content Standard B: Physical Science, properties and changes of properties in matter
Content Standards: Grades 9–12
Content Standard B: Physical Science, structure and properties of matter
Tips
• The flame colors are best observed if the wooden splints are soaked overnight in water. To soak, fill a large beaker about
one-third full with water and put the entire package of wooden splints in the water. They only need to be submerged about
half-way.
• The flame colors are due to the metal in each compound, not the chloride ion. If other metallic salts were used, such as
nitrates [Ca(NO3)2, Cu(NO3)2, LiNO3, NaNO3, KNO3, and Sr(NO3)2], the same results would be observed.
• Avoid mixing the various solids. If mixing occurs, the flames observed will either be mixtures of the two colors, or one of
the colors will mask the other.
• Make sure students fully extinguish the wooden splints by immersing them in a beaker of water before discarding them in
the trash to avoid trashcan fires.
• Have students be careful not to drop excess solid into the laboratory burner. If this happens, the flame will burn the color
corresponding to the dropped solid instead of blue.
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© 2007 Flinn Scientific, Inc. All Rights Reserved.
IN5607
Teacher’s Notes continued
• Depending on the level of your students and your teaching style, you may want to copy the example calculation on the following page and hand it out to your students.
Extensions
• After your students have finished with the lab, test them with this exciting demonstration. Place a scoopful of each metallic
salt in a separate half of a Pyrex® Petri dish. Add enough methyl alcohol to cover the bottom of each dish. Light each dish
individually with a butane safety lighter and have the students determine which metallic salt is in each dish.
• Have students look at the flames through a diffraction grating or piece of Flinn C-Spectra® to observe the line emission
spectra for each metal. Each element has a unique line emission spectrum. Students can sketch the line emission spectrum
for each metal, then use the spectra to identify unknowns.
Example Calculation
Assume a substance emitted light with a wavelength of 450 nm when placed in a flame, but the difference in energy, ΔE,
between the two energy levels is actually desired. The following two steps outline how to calculate ΔE from a wavelength in nanometers.
Step 1—Convert the wavelength from nanometers to meters.
1 meter
λ in meters = λ in nanometers × ————————–
1 × 109 nanometers
1m
λ in meters = 450 nm × —————–
1 × 109 nm
λ in meters = 4.5 × 10 –7 m
Step 2—Substitute into equation 1 and solve for ΔE.
hc
ΔE = —
λ
(6.626 × 10 –34 J•sec) × (2.998 × 108 m/sec)
ΔE = ———————————————————
4.5 × 10 –7 m
ΔE = 4.4 × 10 –19 J
Sample Data Tables
Note: Student interpretations of the flame colors may vary. Allow for slight variation in answers.
Data Table 1
Metal
Color of Flame
Calcium
Orange
Copper
Green
Lithium
Red
Potassium
Violet
Sodium
Yellow
Strontium
Red
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© 2007 Flinn Scientific, Inc. All Rights Reserved.
IN5607
Teacher’s Notes continued
Data Table 2
Metal/Color of Flame
λ (nm)
λ (m)
ΔE (J)
Calcium/Orange
600
6.0 × 10 –7
3.3 × 10 –19
Copper/Green
520
5.2 × 10 –7
3.8 × 10 –19
Lithium/Red
650
6.5 × 10 –7
3.1 × 10 –19
Potassium/Violet
410
4.1 × 10 –7
4.8 × 10 –19
Sodium/Yellow
580
5.8 × 10 –7
3.4 × 10 –19
Strontium/Red
650
6.5 × 10 –7
3.1 × 10 –19
Answers to Post-Lab Questions
1. Use Table 1 in the Background section to record the approximate wavelength of light emitted for each metal in Data Table 2.
See Data Analysis Table.
2. Convert each of the wavelengths in the Data Table from nanometers to meters. Record the wavelengths in meters in Data
Table 2. Show at least one sample calculation in the space below.
Divide each wavelength value in nanometers by 1 × 109 to convert to meters. (This is the same as multiplying each value
in nanometers by 1 × 10–9.) See the example calculation for setup. See Data Table 2 for answers.
3. Use Equation 1 from the Background section to calculate the change in energy, ⌬E, for each metal. Show all work. Record
the values in Joules in Data Table 2.
Use the wavelength values in meters calculated in Question #2 and equation ΔE = hc.
λ
Calcium
ΔE =
(6.626 × 10–34 Jsec) × (2.998 × 108 m/sec)
= 3.3 × 10–19 J
6.0 × 10–7 m
Copper
ΔE =
(6.626 × 10–34 Jsec) × (2.998 × 108 m/sec)
= 3.8 × 10–19 J
5.2 × 10–7 m
Lithium
ΔE =
(6.626 × 10–34 Jsec) × (2.998 × 108 m/sec)
= 3.1 × 10–19 J
6.5 × 10–7 m
Potassium
ΔE =
(6.626 × 10–34 Jsec) × (2.998 × 108 m/sec)
= 4.8 × 10–19 J
4.1 × 10–7 m
Sodium
ΔE =
(6.626 × 10–34 Jsec) × (2.998 × 108 m/sec)
= 3.4 × 10–19 J
5.8 × 10–7 m
Strontium
ΔE =
(6.626 × 10–34 Jsec) × (2.998 × 108 m/sec)
= 3.1 × 10–19 J
6.5 × 10–7 m
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© 2007 Flinn Scientific, Inc. All Rights Reserved.
IN5607
Teacher’s Notes continued
4. Predict the color of the flame if the following materials were heated in the flame. Explain your prediction.
a. Cupric nitrate, Cu(NO3)2—green
b. Sodium sulfate, Na2SO4—yellow
c. Potassium nitrate, KNO3—violet
The colors are predicted by looking at the metal in each salt because it is the metal cation, not the anion, that determines
the color of the flame.
Acknowledgment
Thanks to Sue Zoltewicz, Eastside High School, Gainesville, FL and Otto Phanstiell, Episcopal High School, Jacksonville,
FL for providing us with the idea for this activity.
The Flame Test Kit—Student Laboratory Kit is available from Flinn Scientific, Inc.
Catalog No.
AP5607
AP1714
Description
Flame Test Kit—Student Laboratory Kit
Flinn C-Spectra®, 8⬙ × 10⬙ sheet
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
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© 2007 Flinn Scientific, Inc. All Rights Reserved.
IN5607