Name__________________________________________Period_____Date______________________
Chemistry: Flame Tests
Introduction
In this lab you will investigate a method for identifying metallic ions, flame spectroscopy. Spectroscopy is the
analysis of the light that is emitted by substances that have been energized (that is, excited) by heat or some other
means. The light that is emitted is called the emission spectrum.
The electrons in atoms are located at various energy levels. When an electron absorbs energy, it moves up to a
higher energy level that is farther from the nucleus. When it later releases the energy, it drops back down to a lower
level. The energy that is released is in the form of light that has a definite wavelength and color. Atoms of different
elements have electron levels that differ in their energy. These different kinds of atoms therefore absorb and emit light
of different wavelengths. There are many possible drops the electron can make that each emit different colors. The
wavelengths are characteristic of the different elements and provide an easy way to identify the elements.
We will place solutions of several metal ions in the hottest part of the Bunsen burner flame to see their
individual emission spectra. Because each element on the periodic table has a different number (and arrangement) of
electrons, each element has its own unique emission spectrum. This is an important property of elements; it allows
scientists to determine the composition of many substances from a great distance. In order to see the individual colors
of each spectrum, we would need to view the light through a prism. However, in today’s lab you will be able to
distinguish the different metals from one another with the naked eye alone.
It should be noted that ALL substances emit light when excited. However, today’s flame tests will only reveal
the light emitted by the metal ions in each compound because the light given off by the other components of the
compound are invisible to the naked eye.
Materials: Solutions of several metal ions
Bunsen burner
Wooden splints
Procedure
1. Obtain a splint that has been soaked in one of the compounds.
2. Place the splint in the hottest part of the Bunsen burner flame briefly. Avoid burning the splint if possible,
because the color of the burning wood will mask the color of the excited metal ions.
3. Place the wooden splint on the lab bench until it has cooled. When finished, place all splints in ceramic “solids”
receptacle. If one of your splints falls into the sink, remove it, once it has cooled and place it in the receptacle.
4. Repeat procedures 1-3 for all of the KNOWN solutions. Then test the UNKNOWN solutions. Use your
observations of the known solutions to identify the unknown solutions.
Observations
Record your observations in the provided table.
Ion Tested
+
Li
*FILL IN
THE
IDENTITY
OF THE
UNKOWN
SOLUTIONS
IN THE
BOXES
BELOW
↓
Identity of
Unknowns:
+
Na
+
K
2+
Ca
2+
Ba
2+
Sr
2+
Cu
+
Na
2+
+
K
2+
2+
Cu Ba Sr
UNK #1
UNK #2
Observations
Questions & Analysis:
1. Sketch an atom in the relaxed (ground) state, in the excited state, and then after it has returned to the
relaxed state.
2. Explain how colors observed in the flame tests are produced?
3. Which metals produce similar colors in the flame tests and what does this tell you about their electrons moving
within the atom?
4. Based on your results and observations would the method used in this lab be practical to determine metals in a
mixture? If not, what would you need to make it practical? If it is, explain why you think so.
5. a. What are the wavelengths in nanometers of the strontium & copper ions?
b. Calculate the E released from the strontium & copper ions based on their wavelengths.
sdkfjlskdj(E=hv & c = ʎ v ; 1 m = 1x109 nm)
Sr: ____________________
Cu: ______________________
Questions (Answer Below)
1. Sketch an atom in the relaxed (ground) state, in the excited state, and then after it has returned to the
relaxed state.
2. Explain how colors observed in the flame tests are produced?
3. Which metals produce similar colors in the flame tests?
4. Explain the effect of the chloride ion in solution on the emission of color.
5. Based on your results and observations would the method used in this lab be practical to determine metals in a
mixture? If not, what would you need to make it practical?
6. How are scientists able to determine the composition (that is, how are they able to figure out what they are
made of) of the sun and of distant planets without actually going there?
1.
0 1 2
2. Electrons are excited from the heat Higher e- energy level (for 10-9 sec)  e- falls to a lower energy
level  photon of visible light is emitted at a wavelength that matches the energy input.
0 1 2 3 4
3. Metals with similar colors - Ca & Na  orange; Li & Sr  red; Cu & Ba  green.
0 1
4. Today’s flame tests will only reveal the light emitted by the metal ions in each compound because the light given
off by the other components of the compound are invisible to the naked eye.
0 1
5. The flame test as designed in this lab is not practical to differentiate different metal ions due to
difficulty in discerning color differences of the emitted photons. If a device that could measure the
color difference were employed, then the flame test could be practical in metal ID.
0 1 2
6. Each element has its own unique emission spectrum; it allows scientists to determine the composition of many
substances from a great distance. In order to see the individual colors of each spectrum, we would need to view the
light through a spectrometer/prism.
0
1 2
4. Explain the effect of the chloride ion in solution on the emission of color. (why can you only see certain
wavelengths in the electromagnetic spectrum…)