Flame Test Lab
Prelab assignment: You will need to complete the title, purpose, background information (be
sure to include equation 1 and table 1 along with your background information), storyboard
for each station, and a blank data table for station 1(provided below), 3-8, 9 and 10.
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.
Background:
Absorption and Emission of Light in a Flame
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.
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.
E=hν
(1)
In equation 1,
E is the difference in energy between the two energy levels measured in Joules,
h is Plank’s constant (h = 6.626 x 10-34Jsec)
ν is the frequency in 1/s calculated by c (speed of light)/λ (wavelength)
*Wavelengths are commonly listed in units of nanometers (1 m = 1 x 10 -9nm), 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 arrangement, the electronic
transitions for a given metal are unique. Therefore, 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 Electromagnetic Spectrum
Visible light is a form of electromagnetic radiation. Other familiar forms of electromagnetic
radiation include -rays such as those emitted from radioactive materials and from space, X- rays
which are used to study bones and teeth, ultraviolet (UV) radiation from 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.
Click HERE to see a diagram of the electromagnetic spectrum (or go to page 129 in your book)
The visible portion of the electromagnetic spectrum contains all colors of light. The
wavelength of the radiation determines the color of the light. In table 1, below are the wavelength
ranges for the various colors of light.
Table 1
Representative
wavelength, nm
410
470
490
520
565
580
600
650
Wavelength Region,
nm
400-425
425-480
480-500
500-560
560-580
580-585
585-650
650-700
Color
Violet
Blue
Blue-green
Green
Yellow-green
Yellow
Orange
Red
Procedures: This is a station lab; you will start at an assigned station and then move to other
stations.
Station 1: ID of gas in discharge tube – Look through the eyepiece of the spectroscope to
observe the emitted spectrum from the discharge tube. Record all colors observed and their
corresponding (in nanometers).
Color of Line
Observed
Wavelength
(nm)
Station 2 results
Station 2 results
Station 2 results
Wavelength (m)
Frequency (s-1)
Energy (J)
Station 2: Discharge tube calculations – You will do this station at your seat while you are
waiting to go to another station.
1. Using the first wavelength in your table show the work for the conversions to meters, frequency,
and energy in your lab notebook under the heading “Station 2 Calculations”. Go back and
enter the results of these calculations into your station 2 data table.
2. Convert the other wavelengths to meters, frequency, and energy and enter into your data table.
(You do not need to show work for these calculations).
Station 3 – 8 Flame Tests
1. Take a control stick (soaking in distilled water only) and place it in the Bunsen burner flame.
Do not leave it in the flame for long (the stick should NOT catch fire). Record your
observation of the color as the control in your data table. You only need to do the control
test one time.
2. Take a stick that is soaking in the metal chloride solution and put it in the Bunsen burner
flame. Observe the color of the flame and record it in your data table along with the formula
for the metal chloride. Do not leave it in the flame for long (the stick should NOT catch
fire).
3. In all cases the used sticks should be placed in the beaker labeled USED STICKS at the
station.
Station 9 – Data Analysis for stations 3 – 8 - Like station 2 you will do this after you have
completed stations 3 – 8 and it will be completed at your desk.
Look at the color you observed for the six metal chloride solutions and estimate the wavelength of
each using Table 1 above. Record this data under the heading “Station 3 – 8 Analysis” in your
lab book.
Station 10 – Unknown Flame Tests – this will be done as a class demonstration at the end of the
lab. I will burn each of the metal chlorides and you will attempt to identify each using your data
from stations 3 – 8. You will record this data in a data table with the heading “Station 10 Data”
which should include a column for the sample number (1-6), the color observed, and your guess as
to which metal chloride the unknown is.
Post Lab Analysis questions:
1. Convert each of the wavelengths recorded in the “Station 9 Analysis” step from nanometers to
meters. There should be 6 – one for each chloride solution.
2. Use ν = c/λ to calculate the frequency for each chloride solutions wavelength. Show your work
for each calculation. The unit for your answer is 1/s (which means number of waves per
second).
3. Use ΔE = hν to calculate the change in energy for each chloride solutions energy. Show your
work for each calculation. The unit for your answer is Joules, J.
4. What happens to the wavelength of light as its energy increases?
5. Paper logs soaked in solutions of metal salts and dried are sold for producing colored flames in
fireplaces. If you were producing one of these logs explain which compounds you would use,
and why you would use them, to produce a flame to celebrate …
Halloween?
Christmas?
Easter?
6. The compounds that were tested are all considered salts. This is because they are made of a
metal and non-metal. The metal is always written first in the formula and the non-metal is
written second. Which part of the salts tested do you think produced the color – the metal or
the non-metal? Use the formulas for the compounds to explain your answer.
Conclusions:
1. Briefly explain what you learned by doing this lab.
2. Also, give some reasons why you may not have been able to identify the solids correctly
when I did the demonstration.