SCH4U1: FLAME TEST LAB. INVESTIGATION
APPLICATIONS OF EMISSION SPECTRA
The coloured lights given off by neon signs, streetlights, signal flares, fireworks, and even distant stars all
result from excited electrons moving from higher to lower energy levels in atoms. Each element has a
unique emission spectrum, so when element are heated in a flame, they will give the flame a
characteristic colour. We can use this technique to identify elements even when they are parts of
compound. We can also determine the amount of the element present by measuring the intensity of the
light emitted. This technique, called flame emission spectroscope; is used in many situations, including
analyzing and establishing the geographic origin of ancient pieces of pottery.
CREATING A FLAME TEST KEY
Some elements show one or more particularly prominent lines in their line spectra. We can make use of
this phenomenon to find out which metal is present in an unknown metallic compound. In this test,
called Flame Test, the unknown sample is heated in a flame. The colour of the flame is observed and
compared against a chart of known flame colours.
You are in this activity to observe and create a key for, the colours produced when solutions or solids of
known metal compounds (mostly Group 1 and 2 mental) are heated to high temperature. You will be
able to use this key to determine the identity of unknown metallic compounds. To establish this key, you
will draw compounds from solids using wire, and then put the end of the wire into a flame.
MATERIALS
Eye protection
Nichrome test wire
Watch glasses
Crucible tongs
Laboratory burner
Hydrochloric acid, dilute, 10ml
Sample of the following solids
Sodium chloride (Solution)
solid sodium chloride
Sodium nitrate
Calcium chloride
 Strontium chloride
 Lithium chloride
 Potassium chloride
 Copper(11) chloride
 Unknown Samples A, B, C
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PROCEDURE
1. Obtain your samples (the solids and 3 ml of the sodium chloride solution in a small test tube)
and the 10-ml hydrochloric acid solution (also in a small test tube). Store the test tubes in a rack.
2. Light the laboratory burner and adjust it until it is burning with a blue flame.
3. To clean the nichrome test wire, dip it in the hydrochloric acid, and then hold the wire in the
flame of the laboratory burner. Repeat the procedure until the wire adds no colour to the flame.
4. Pick up a small amount of solid sodium nitrate with the wire loop. Hold the end of the wire in
the flame. Record your observation.
5. Clean the wire as in step 3.
6. Pick up a small sample of solid sodium chloride on the wire loop. Hold the end of the wire in the
flame for several seconds. Record your observations.
7. Clean the wire as in step 3.
8. Dip the nichrome rest wire in the sodium chloride solution. Hold the end of the wire in the flame
and record your observations.
9. Repeat the step 4 with each of the solid samples, remembering to clean the wire after each test.
Record your observations.
ANALYSIS
(a) Assemble your observations into an identification key that you could use as a quick reference.
(b) Using your reference key, identify the metals in the three unknown samples
(c) Compare the results of your flame tests for solid sodium nitrate, solid sodium chloride, and
sodium chloride solution. What do these results indicate?
Discussion Questions
1. As far as we know, people from all cultures have been interested in the stars. Modern astronomers
use spectroscopy to analyze starlight. What information could these observations provide?
2. According to the Bohr theory, what happens to an electron in an atom as it absorbs energy and as it
releases energy?
3. Spectral lines are the fingerprints of elements. “Explain what is meant by this statement.
4. When fireworks explode they produce a variety of colours.
(a) Provide an explanation for this observation, referring to emission spectra and energy levels.
(b) Suggest compounds that could be used to produce several specific fireworks colours. Comment on
any practical difficulties that might result from your choices.
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