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
Also, I have produced a video suitable as an introduction
to this lab. It may also be viewed by students who were
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
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. This requires experience and is based on
a comparison between the color observed and the known
colors produced by different metallic salts. It is a
traditional art of the chemistry laboratory to use these
colors to identify specimens of compounds that contain
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
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 chemicals directly
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
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 Chloride
Color of Flame
Approx. Wavelength (nm)
Approx. Wavelength (m)
Clean the inoculation loop by swirling it gently in the
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
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
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 but including details of their basic construction and operation
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?
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
What has to happen to the electrons in atoms in order for them to produce light in an element’s characteristic color?
Why do the chemicals have to be heated in the flame
before the colored light is emitted?
When an electron drops from a high energy level to a lower one, it emits a photon. If the energy change is large then the wavelength is small. If the energy change is small, then the wavelength is large. Which represents a larger change in energy, a red photon or a blue one?
Why do different metals have different characteristic
flame test colors?