FLAME TEST LAB

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Flame Test Lab
12/09/13
OHS Chemistry
Background:
The normal electron configuration of atoms or ions of an element is known as the
"ground state". In this most stable energy state, all electrons are in the lowest energy
levels available. When atoms or ions in the ground state are heated to high temperatures,
some electrons may absorb a specific amount of energy (a quantum) to allow them to
"jump" to higher energy levels. The element is then said to be the "excited state". This
excited configuration is unstable, and the electrons "fall" back to their normal positions of
lower energy.
As the electrons return to their normal levels, the energy that was absorbed is emitted in
the form of electromagnetic energy. Some of the energy may be in the form of visible
light. The color of this light can be used as means of identifying the elements involved.
Such crude analyses are known as flame tests.
Only metals, with their loosely held electrons, are excited in the flames of a laboratory
burner. Thus, flame tests are useful in the identification of metallic ions. Many metallic
ions exhibit characteristic colors when vaporized in the burner flame.
PURPOSE:
Observe the characteristic colors produced by several metallic ions when vaporized in a
flame. Identify an unknown metallic ion by means of its flame test.
EQUIPMENT and MATERIALS:
Laboratory burner
Safety goggles
Q-tips
Diffraction grating
Cobalt Blue Glass
Aprons
Beaker
Colored pencils
Cation Solutions (each 0.5 molar solution contains a metallic ion with a NO3  anion):
Na+, K+, Li+, Ca2+, Sr2+, Ba2+, Cu2+, B+3
Unknown Solutions
PROCEDURE:
1. Put one end of a Q-tip into a solution bottle, being careful not to touch the other end.
2. Insert the moistened Q-tip end into the hottest part of the flame, allowing the chemical
solution to burn, showing its characteristic color. Avoid leaving the Q-tip in the flame
too long as the Q-tip itself will begin to burn and its burn color may be confused with
the ion color.
3. Observe and record any new colors noted in the flame.
4. Perform a second test using the unburned end of your Q-tip.
5. Discard Q-tips in the large beaker after both ends have been used or if any
contamination occurs. Do not put the Q-tips in the trash.
6. Repeat the first 5 steps using the other known ion samples until a definitive flame
color can be observed for each solution. Record data.
7. Using the diffraction grating view the flame’s spectrum. Using colored pencils
record the bright line spectrum in your data table
8. Repeat the same steps for the three unknown solutions. Record data. Match your
results for each unknown to one of the seven known chemicals previously tested.
Record.
IMPORTANT NOTES:



Be VERY careful not to contaminate bottles of metal nitrate solutions.
Cobalt blue glass may be used with the potassium ion solution to filter out
interfering wavelengths of light. View the flame through the glass.
It is helpful to lower the light level in the room to achieve better contrast.
OBSERVATIONS AND DATA:
Metallic
Ion:
Color of Flame
Spectrum
Ca2+
Li+
B3+
K+
Ba2+
Na+
Cu2+
Sr2+
Identity of Unknown
Unknown
1
Unknown
2
Unknown
3
QUESTIONS:
1. Which pairs of ions produce similar colors in the flame tests? What can be done
to avoid confusion in your identification of these ions?
2. Define these terms:
(a) quantum
(b) ground state (c) excited state
3. What is a spectroscope? What is observed if the flame tests are viewed through a
spectroscope?
4. This is a qualitative lab. How could it be modified to quantify the data? i.e. What
kind of measurements could be made to determine the amount and/or type of
colored light emitted?
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