LAB: FLAME TEST STUDY (14 points)
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OBJECTIVE: After completing this lab students should be able to identify the color several atoms
can impart to a flame.
APPARATUS: burner and tubing; two cobalt glass plates; several test tubes; platinum inoculation
wire
MATERIALS: 3M HCl (hydrochloric acid)- skin irritant
0.5M Ba(NO3)2 (barium nitrate)- poisonous
0.5M Ca(NO3)2 (calcium nitrate)- poisonous
0.5M LiNO3 (lithium nitrate)- poisonous
0.5M KNO3 (potassium nitrate)- poisonous
0.5M NaNO3 (sodium nitrate)- poisonous
0.5M Sr(NO3)2 (strontium nitrate)- poisonous
0.5M NaCl (sodium chloride)- can cause high blood pressure
NaCl (sodium chloride)- -----------------unknown solution- could be poisonous
INTRODUCTION:
When an atom is heated weather with electricity or in a burner flame, its electrons absorb low
energy photons and go to higher energy levels. As these pumped-up electrons cool, the electrons
return to the ground state. In the process of falling the electrons usually release photons of visible
light. The color of the photon depends on the amount of energy it has. Each atom has its own
unique collection of photons that it can emit. This unique photon pattern is like an atomic
fingerprint that can be used to identify the presence a particular atom. When a solution contains
several atoms the color patterns emitted can be very difficult to interpret. A spectrophotometer is a
expensive machine used for complex photon pattern interpret. This machine sends the emitted
light through a prism. Light coming out of the prism is separated into its component parts called a
bright line spectrum. A computer then compares this complex spectrum to the spectrum patterns
of known atoms. Eventually it will generate a list of all atoms present. The spectrophotometer is
only good for qualitative analysis and can not be used to determine the amount of material in a
solution.
A metal hooked to a non-metal can be called a salt. The non-metal part can be a collection of
non-metals called a radical. In this lab you will investigate if the metal ion or the radical imparts
color to the flame. Once you have established the color caused by known atoms, you will use this
information to identify the presence of atoms in an unknown. The technique described in this lab is
very sensitive, so be sure glassware and platinum wire are very clean.
PROCEDURE:
1. Clean several 4 mL test tube by scrubbing with detergent, followed by a tap water rinse,
followed by a DI water rinse. Don't dry these test tubes. Obtain approximately 2 mL 3M HCl.
Clean a platinum wire by dipping it first into the dilute HCl and then hold it in the colorless flame
of your burner. Repeat until the wire imparts no color to the flame.
2. Pour approximately 10 drops 0.5M NaNO3 into a test tube and dip the tip of the clean platinum
wire into the solution, then hold it in the flame. Note the color of the flame just above the wire.
Observations:
Names in Lab Team: ______________________________________________ period ________
Lab: FLAME TEST STUDY (14 points)
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PROCEDURE: (continued)
3. Clean the wire as before and then test a solution of NaCl in a similar manner. Repeat the test
by dipping the wire in dry NaCl.
Observations:
Does the metal or non-metal radical impart color to the flame? ___________
4. Repeat procedure two using instead LiNO3, Sr(NO3)2, Ca(NO3)2, Ba(NO3)2, and KNO3. Clean
the wire thoroughly after each test and record your results in the data table.
5. If two salts are present in a solution, the color of one flame may mask the color of the other
flame. Sometimes it is possible to filter out one flame and not the other. Examine a sodium
flame through two thicknesses of cobalt glass. Examine a potassium flame through two
thicknesses of cobalt glass. Record your results in the data table.
Observations:
6. Combine 5 drops KNO3 and 5 drops NaNO3 and record the color the mixture imparts to a flame.
Now record the observed color imparted to the flame through two thicknesses of cobalt glass.
7. Test and identify the atom(s) present in the unknown.
Data Table (4 point)
atom in solution
Na
color of flame
Questions: (2 points each)
1. Is flame coloration a test for the metal or the
non-metal?
2. Why do NaCl solution, NaCl solid, and NaNO3
all produce the same color flame?
Li
Sr
3. Describe how you would test an unknown for
the presence of both sodium and potassium?
Ba
K
Na (with Co glass)
K (with Co glass)
4. What difficulties maybe encountered when
using the flame test for identification?
Ca
Na & K
Na & K
(with Co glass)
unknown
5. What is the identity of the unknown metal?