Spectroscopic Investigation of Metals in a Solution
Introduction
The purpose of this lab was to identify elements using a spectrometer, a tool used to
measure the wavelength of an atomic emission spectrum line. Spectroscopy is the
study of spectra produced when matter emits electromagnetic radiation. This
concept is used in identifying and discovering new elements and substances as no
two elements have the same set of spectrum emission lines. It has played a major
role in the making and refinement of atomic models of the atom, for instance the
Bohr and the quantum mechanical models. The Bohr model represents the atom as a
positively charged nucleus with negatively charged electrons circling on orbits
(energy levels) around it. When the electron is closer to the nucleus it has less
energy, as opposed to when it is on one of the farther orbits it has more energy. In
his model, the electron moves along theses orbits at a constant rate until energy is
added. When that happens the electron “jumps” to a new orbit and continues
circling the nucleus. When the electron jumps to a lower orbit and releases energy,
however, it creates an atomic emission spectrum line. The color of that spectrum
line depends on how far the electron jumps and how much energy is being released.
The most recent and accurate model, the quantum mechanical model, explains that
the electrons are not in one specific place on an orbit, they are somewhere within
the electron cloud, still with a specific amount of energy but no certain location.
Part 1: Qualitative Investigation.
Results
Table 1
Compounds
NaCl
CuCl2
LiCl
KCl
CaCl2
SrCl2
CaCO3
Na2CO3
K2SO4
CaSO4
Unknown 4
Unknown 5
Flame color
Bright orange
Bright green, some orange
Light red, pink, orange
Light orange, white
Dark orange
Dark red
Bright green, orange
Bright orange
Light purple, orange, pink
Bright green, light orange
Bright orange
Dark pink, orange
The color of the flame for each
compound is recorded in Table 1.
Discussion
Safety concerns: Open flames. Hair and loose clothing must be tied back, safety goggles
must be worn at all times.
The first part of this experiment was the qualitative investigation. The purpose of
this section was to determine what element or compound was present in the
solutions provided based on the color of the flame produced when that solution was
stuck into the flame. To do this, small pieces of melamine foam were soaked in test
tubes containing labeled and some unknown compounds. When the pieces of foam
were put into a flame they emitted a certain color. The color of the flame depends
not on the solution the foam was soaked in but on the cations in that solution. When
the cations are heated or “excited” they jump around gaining and releasing energy,
that is when the light is produced. The metals in the flame are what caused the
distinct colors. (Ca, Cu, Na, Sr, K and Li). The solutions with these metals in them had
similar flame colors.
Based on the data collected, Unknown solution 4 could be either NaCl or Na2CO3
because all three of these solutions had the bright orange color flame. Unknown solution
5 most likely contains Lithium because both Unknown 5 and LiCl had the distinct dark
pink, light red color flame.
Part 2: Spectrometer
Results
Figure 1
Sample KCL. Intensity: 541.3nm (.052 rel), 576.3nm (.071 rel), 771.9 nm(.0721 rel).
Figure 2
Sample LiCl
Wavelength vs. Corresponding intensity: 540.9nm (.0367 rel), 576.3nm (.0417 rel),
670.3nm (0.054 rel).
Figure 3
Sample NaCl
Wavelength vs. Corresponding intensity: 542nm (.034 rel), 576nm (.037 rel),
581nm (.038 rel)
Figure 4
Sample SrCl2
Wavelength vs. Corresponding intensity: 541nm (.031 rel), 578nm (.037 rel),
605nm (.043 rel), 672nm (.0395 rel), 684nm (.0455 rel)
Figure 5
Unknown Sample 6
Wavelength vs. Corresponding intensity: 542.5nm (.035 rel), 576.3nm (.043 rel),
771.9nm (.067 rel)
Discussion
Safety concerns: Open flames. Hair and loose clothing must be tied back, safety goggles
must be worn at all times.
Part to was the spectrometer section. The purpose of this section was to use the
electronic spectrometer to determine the wavelength and intensity of specific
compounds and elements. With the same principle as a spectrometer, this tool can
help scientists determine and discover elements.
The data collected from this section of the experiment shows that unknown solution
6 may contain potassium because it has the same intensity of 771.9nm as sample
KCL, lithium because it has an identical peak of 576.3nm as sample LiCl, and
chlorine with a shared peak at 576nm with sample NaCl.
Part 3: Spectrum Tube Analysis with a Spectroscope
Results
Figure 1
Figure 2
Figure 3
Discussion
Part three of this experiment was conducted with a spectrometer and 3 unknown
spectrum tubes. Looking through the spectrometer, the emission spectra lines
become visible and were recorded on the “Visible Spectrum” data sheet. Unknown E
is believed to be magnesium because the emission lines on the visible spectrum seen
through the spectrometer match up almost perfectly with those on the Various
Chemical Elements chart of the element magnesium. Comparing the rest of the
elements to the Atomic Emission Spectrum of Various Chemical Elements chart, it
can be concluded that Unknown F is lithium and Unknown D is hydrogen.