Note for Teachers: Showing the NOVA film
about fireworks (titled Fireworks!) before or after this lab
activity may enhance the learning it is meant to produce.
Also, I have produced a video suitable as an introduction to this lab. It may also be viewed by students who were absent.
In this lab students will learn about atomic energy levels,
emission spectroscopy, and flame tests for element
Students will use small samples of 6 chloride salts of
different metals. These they will place into a flame in order
to observe the colors produced. These colors come from the
excitation of electrons which then resume their ground states
by emitting light of very specific colors.
The electrons in an atom occupy different energy levels, as
you know. When all of the electrons are at the lowest possible
energy level they are said to be in the ground
state. Electrons do not always stay in the ground
state. Sometimes they can be promoted to a higher-energy
electron shell. This can happen in two ways. First, the
electron can absorb a photon of just the right amount of energy
to move it from one quantum shell to another. Second, when
atoms are heated or energized with electricity their electrons
can gain energy. This promotes them to the higher-energy shell.
When an electron is in a higher-energy shell it is said to be
in an excited state.
Electrons in excited states do not usually stay in them for
very long. When electrons lose their energy they do so by
emitting a photon of light. Photons are particles with energy
but no mass. Their energy is directly proportional to the
frequency of the light (remember: E = hf). The photons emitted
precisely match the quantum energy difference between the
excited state and the ground state.
The light produced by very hot atoms in the gaseous state is
a unique spectrum for each element. To observe the spectrum
requires the use of a prism, diffraction grating, or
spectroscope. Before complex instruments were invented to
observe elemental spectra chemists sometimes identified metals
in compounds by doing a flame test. Salts are a type of
compound that include a metal and a non-metal. Sodium chloride
(NaCl) is the most familiar
example of a salt but others include calcium
copper(II) chloride (CuCl2). In flame tests salts that
are dissolved in water are evaporated using a hot flame. In the
flame the metal atoms become excited and produce their
characteristic spectrum of light. However, since the observer
does not use a spectroscope only one color is observed. It
turns out that many metals produce a unique single color under
these conditions. Some metals do produce very similar colors
but a practiced eye can often distinguish them. It is a
traditional art of the chemistry laboratory to use these colors
to identify specimens of compounds that contain unknown
This ability of metal atoms to produce these colors is put
to use by practitioners of the art of fireworks manufacture. By
including different metal salts, or mixtures of metal salts, in
the exploding shell of a firework, these artists can produce
beautiful displays in nearly all the colors of the rainbow.
10 small beakers per lab table
one for distilled water
9 for the samples and unknowns
1 inoculation loop
Or a set of cottom swabs
1 Bunsen burner
sharpie for labeling
a series of metal chloride solutions such as CaCl2, CuCl2, LiCl, KCl,
NaCl, CsCl, and SrCl2
(these will be provided in dropper bottles)
2 unknown metal chlorides
Wear goggles or risk sitting out the lab
Treat all chemicals in this lab as toxic. Do not touch
any of them with your bare hands.
Wash well with water immediately if you touch chemicals
Use caution with the burner
Do not leave burner unattended
Place burner near middle of lab bench
Tie back long hair
Do not wear baggy clothing in the lab
Hot objects look like cold objects: be cautious!
Chloride) is highly toxic by ingestion; avoid contact with
eyes, skin and mucus membranes.
LiCl (Lithium Chloride) is
moderately toxic by ingestion; avoid contact with eyes, skin
and mucus membranes.
Wash your hands with soap and water after you complete
the day’s lab work, even if you didn’t touch any
Remember to record your observations in your lab notebook or
on a piece of paper in your binder before you leave
class. When making observations be sure to use all of your
senses except taste. Never taste anything in the chemistry lab.
Chances are good you will regret it if you do.
400 - 440
440 - 470
470 - 490
490 - 560
560 - 570
570 - 585
585 - 630
630 - 700
You will share a set of metal salt solutions with the people at your lab station. At least four people should share a set to reduce the number of beakers to be washed and the amount of chemical waste. Label all of your beakers. Label one for the water rinse. Either 50-mL or 100-mL beakers
will be fine.
Collect a small sample (a few drops) of each of the
known metal salt solutions which your teacher has provided
and carry them all to your lab bench.
Obtain an inoculation loop for your group.
Obtain 10 - 20 mL of distilled water in your labeled beaker.
Each group member must record information in a neat table
with the following columns. Make this table before you even
turn on the gas.
Name & Formula of Metal
Color of Flame
Approx. Wavelength (nm)
Approx. Wavelength (m)
Clean the inoculation loop by swirling it gently in the
distilled water. Then, once you light the burner,
heat the loop until it glows red hot. This step removes any
ions clinging to the loop.
Light and adjust your Bunsen burner. Be sure to clean
your loop carefully. Do not leave the loop in the
flame too long as it can cause the loop to degrade and
To do a flame test with each metal salt get a film of the
solution of a salt inside the loop and bring it into the
hottest part of the flame. If this produces poor color then try the edge of the burner flame. Repeat the dip into the salt
solution as often as necessary to see the flame test color.
Be sure not to over-heat the loop.
Carefully note the color of each metal salt when it is
put in the flame. Use the chart on the previous page to
estimate the approximate wavelength of the color you see. Use
the Representative Wavelength values. Record all data in the
table you made earlier.
Clean the inoculation loop using distilled water and heat each time you change from one metal salt to another.
Failing to do so will result in mixed flame test colors.
Again, do not over heat the loop.
Clean out the beaker using the method recommended by your
instructor (hazardous wastes must be disposed of properly).
Usually, all leftover solutions will be collected in
designated waste containers for hazardous waste
Wash all equipment carefully and thoroughly using the tub
of soapy water provided. By gently scrubbing the beakers with
a brush and the soapy water you will be able to wash off the
labels you put on them. Please do so!
Your teacher has prepared two solutions with two of the
metal salts. They are labeled Unknown 1 and Unknown 2. Your
teacher will demonstrate their flame test colors for the
As a class, discuss which element you think the unknowns
represent and ask your teacher to demonstrate the flame test
colors of the elements you think are the correct ones.
For this lab you must turn in the following items:
Your data table recording flame test colors and
Answers to the following questions
A one-page essay about how fireworks are made,
concentrating on how they produce different colors
Why do different metals have
different characteristic flame test colors?
Most salts contain a metal and a
non-metal. Look at the compounds we tested and determine
whether it is the metal or the non-metal that is responsible
for the color produced in the flame test for that salt. How
can you be sure your answer is correct?
What colors did the unknowns produce
in the flame? What are the unknowns?
Why do the chemicals have to be
heated in the flame before the colored light is emitted?
Could flame tests be useful in
determining identities of metals in a mixture of two or more
salts? If so, what problems might arise? If not, why not?
Explain your answer.
Which method is better for precisely
identifying elements: examining the full spectrum using a
spectroscope or using a flame test? Use your experience in
the lab with both of these methods in answering this
question. Justify your answer.