Flame Test Lab
Group name: The Dough Boys
B. Silly
Lab Partners
N.O. Kidding
I.M. Goofy
O. Really
Introduction
The first spectroscopes’ invention is accredited to Gustav Robert Georg Kirchoff and Robert
Wilhem Bunsen. Early spectroscopes were prisms with graduations marking off the wavelengths
of light. Later spectroscopes worked by allowing light through a slit into a collimating lens that
transforms the light in to a thin beam of parallel rays. The light then passes through a prism that
refracts the beam into a spectrum. With the spectroscope, we can measure properties of light like
wavelength and intensity. Using the equation E = hc/λ, one can find the energy of the spectra or
emissions lines created and measured by the spectroscope.
One can indentify a metal by its unique emissions spectrum produced when heated in a flame.
This is caused by electrons without sufficient energy remain in a higher energy level falling back
to a lower one emitting energy as a photon of light. In this lab, seven metal salt compounds are
put in a flame to observe and measure their emissions spectra. The emissions spectra will be
observed and the emission lines’ energy will be calculated using the wavelengths observed
through a spectroscope.
Experimental
Seven different metal salt compounds—KCl, SrCl2, CaCl2, LiCl, NaCl, CuCl2 and BaCl2—were
mixed with distilled water to create a paste. The compounds are placed in a number twelve well
tray and carefully kept track of. About the tip of a scoopula full of each compound is used. The
Bunsen burner is then lighted and trimmed. J The nichrome wire is cleaned by putting it in the
flame and dunking it in a beaker full of distilled water. The wire is considered sufficiently clean
when the wire in the flame emits no color when first placed into the flame. The wire is then
dipped into the first well containing the first metal salt compound. The wire now covered in the
compound is placed in the flame and the flame color is recorded. The flame is viewed through
the spectroscope to see the emissions spectra. The flame color and the two most prominent
emission lines’ wavelengths are recorded the wire is then cleaned using the same process as
before and the compound in the next well is put into the flame until the process is completed for
all of the compounds
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Results and Discussion
The following table items are the results and calculations from the experiment.
Wavelength
Compound
Flame color
Line 1 (nm)
Line 2 (nm)
Energy
Line 1 (J)
Line 2 (J)
-19
4.4 x 10-19
KCl
Purple-pink
600
450
3.3 x 10
SrCl2
Dark red
620
680
3.2 x 10-19
2.9 x 10-19
CaCl2
Orange
600
570
3.3 x 10-19
3.5 x 10-19
LiCl
Fuchsia
670
590
3.0 x 10-19
3.4 x 10-19
NaCl
Yellow
600
550
3.3 x 10-19
3.6 x 10-19
CuCl2
Green
600
560
3.3 x 10-19
3.5 x 10-19
BaCl2
Yellow-green
590
550
3.4 x 10-19
3.6 x 10-19
The colors of the flame are caused by electrons that when heated become excited and move to a
higher energy level. When the electrons no longer have the energy to stay in that energy level,
they fall back to a lower energy level. The excess energy from the differences in the energy
levels is released in the form of a photon of light. The different colors are created because the
photon’s energy is based on how much energy the falling electrons release. The electrons that
fall from higher energy levels release more energy than an electron that falls from a lower energy
level. The more energy released the closer the light is to violet in the spectrum. A lower energy
release is closer to the red side of the spectrum.
The elements that are farther down the periodic table seem to have emissions closer to the violet
end of the spectrum while the elements higher up in the periodic table have emissions closer to
the red end of the spectrum. This is somewhat unexpected. The elements higher up on the
periodic table have fewer electrons and so are more tightly held by the nucleus. Because they are
more tightly held, it should require more energy to excite and electron, which means more
energy would be given off when that electron returns to a lower energy level.
The only truly
green flame was produced by the only transition metal cation used in this experiment. This
suggests that the presence of electrons in the d-orbitals affects the observed color of the flame.
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There are many sources of possible error in this lab.
The same wire was used for each
compound which means that there is the possibility that residue from the previous compound
could have been present in the next burning. This would cause an inaccurate reading with the
spectrometer and therefore and inaccurate energy calculation. Another error could come from the
fact that certain compounds had to be held to the Bunsen burner flame in a very specific manner
in order to get the correct flame color. If the compounds were held incorrectly, the data would be
wrong. Another area where we could have accrued error is in the reading of the spectrometer.
The emissions sometimes lasted for only a few short seconds and so an accurate reading was
harder to get. In general, imprecise tools and inconsistent procedures can account for most of the
error in this lab.
Conclusion
The energy of metal salt compounds’’ emission lines when heated were examined in this lab. It
was found that elements that released the highest energy photons tended to be closer to the
bottom of the periodic table. For example, lithium (atomic number 3) had emission lines of 670
nm and 590 nm while barium (atomic number 56) had significantly shorter wavelengths of 590
nm and 550 nm.
Peer evaluation
N.O. Kidding: 2 (note: he spent too much time goofing around)
I.M. Goofy: 5
O. Really: 4
Sample calculations
KCl line 1 energy: E = hc/λ
E = (6.626 x 10-34 Js)(3 x 108 m/s)/(6.00 x 10-7 m) = 3.3 x 10-19 J
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