Nick DiPreta
Jonny Masci
Mr. Cimonella
Period ¾
Due Date: 12/16/09
Pre-Lab: The normal electron configuration of atoms or ions is known as the “ground state”.
When atoms or ions in the ground state are heated, electrons may absorb enough energy to
jump up to higher energy levels. This is called the elements “excited state”. In this situation,
the configuration is unstable, and the elections “fall” back into their normal positions of the
lower energy. When the electrons return to their lower energy levels, the energy that was
absorbed is emitted in electromagnetic energy, some of which can be in the visible form. When
it is in the visible form, the color of the light can be used to identify what element it is. This can
be done by doing experiments such as the flame test. Only metals are excited in the flam of a
lab burner. Flames are useful in the identification of metallic ions. Many metallic ions exhibit
characteristic colors when vaporized in the burner flame.
Purpose: Therefore, the purpose of this experiment is to observe the characteristic colors
produced by certain metallic ions when vaporized in a flame. Then, identify an unkown metallic
ion by performing the flame test.
Equipment
Graduated cylinder, 10-mL
Bunsen burner
Test tubes 13X100 mm (8)
Test tube rack
Wire loop
Glass-marking pencil
Safety goggles
Lab apron/coat
Materials
HCL (conc)
Unidentified solutions
0.5 M solutions of nitrates of Na+, K+, Li+, Ca2+, Sr2+, Ba2+, Cu2+
Safety
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Handle the highly concentrated HCL with great care.
Report spills to your teacher and flush them with cool water and NAHCO3 solution
Wear safety goggles and lab apron
Tie back all loose things
Be careful around the flame.
Procedure
1. Measure 5mL of tap water in a graduated cylinder and pour the water into a 13X100
test tube. Using a marking pencil, mark the outside of the tube to indicate the level of
the water. Discard the water. Using the marked tube as a guide, mark seven clean test
2.
3.
4.
5.
6.
7.
tubes at approximately the same level. Place the clean tubes in a test tube rack. Set the
other test tube aside.
Into each of the clean test tubes, pour 5mL of a different nitrate solution. Mark each
test tube to indicate the metallic ion it contains.
Pour about 10 mL of concentrated hydrochloric acid into a 50-mL beaker. To clean the
wire loop, dip the loop into the acid, and then heat the loop in the outer edge of the
burner flame. Continue to clean the loop in this manner until no color is observed in the
flame
Dip the clean wire loop into one of the nitrate solutions. Place the loop in the outer
edge of the burner flame and move the loop up and down. Note the color in the flame.
Record your observations in the data list provided.
Clean the wire loop as described in step 3. Repeat step 4 using a different nitrate
solution.
Test each nitrate solution in the same manner, cleaning the loop thoroughly between
the tests. Record all your observations in the data list.
Obtain a sample of an unknown solution. Perform a flame test and identify the metallic
ion present by the color of the flame.
Observations and Data
Metallic Ion
Na+
K+
Li+
Ca2+
Sr2+
Ba2+
Cu2+
Unknown (Li+)
Color in Flame
Orange
Violet
Red
Lime Green
Red
Dark red
Greenish Yellow
Red
Questions and Conclusions
1. What inaccuracies may be involved in using flame tests for identification purposes?
Several different metallic ions may appear to have the same color when used in the
flame test. This may lead to one believing that an ion is being represented by a flame when
really, it could be several different ions.
2. What pairs of ions produce similar colors in the flame tests?
Ca2+ and Cu2+ both produce light green colors. Sr2+ and Li+ both produced very similar red
colors.
3. Explain how the colors observed in the flame tests are produced.
When atoms or ions in the ground state are heated to high temperatures, such as that when
heated by a Bunsen burner, some electrons may absorb enough energy to allow them to
“jump” to higher energy levels. The element is then in the “excited state”. This configuration is
unstable and the electrons want (and do) return to their normal levels. When they do this, the
energy that was absorbed is released in the form of electromagnetic energy. Much of this
energy emitted is in the form of light.
4. Define these terms. A. quanta B. ground state C. excited state
A quantum or quanta (plural), is the smallest distinct quantity of some physical property that a
system can possess. The normal electron configuration of the atoms or ions of an element is
known as the “ground state”. This is the most stable energy state, and all electrons are in the
lowest energy levels available. The excited state is present when atoms or ions in the ground
state are heated to high temperatures, and some electrons absorb enough energy to “jump up”
to higher energy levels.
5. What is a spectroscope? What is observed if the flame tests are viewed through a
spectroscope?
A spectroscope is and instrument used to view a light source so that it is split into its
component colors. If the flame tests were viewed through a spectroscope, we would see a
graph of the separated specific colors that make up the flame. This is known as a spectrograph.
This spectrograph can be used to fingerprint what element it is.