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Supernova Chemistry Student Handout |
SAFETY
Wear safety glasses throughout this activity. The
devices used in this experiment to power the gas-
filled tubes use a very high voltage of
electricity. Do not remove the gas-filled tubes or
insert metal objects such as pens or paper clips
into the power devices. The gas-filled tubes will
be very hot to the touch, so be careful to not
touch the surfaces.
INTRODUCTION
Atomic spectroscopy is an extremely important tool
for scientists. Because the electron patterns
around every kind of atom are unique, and because
these electrons interact with light in different
ways because of their different positions, you can
determine what kinds of atoms are present in a
substance by the kind of light absorbed or emitted
by the substance. Every atom has a kind of
"fingerprint" in the normal light spectrum that is
measured with a device called a Spectrometer. This
instrument uses a diffraction grating as a prism,
splitting the incoming light into its composite
colors.
As an example, a marine ecologist may suspect that
the reason many bottom-dwelling organisms are dying
in a local harbor is because of a chemical
pollutant. She samples the mud and chemically
extracts a type of metal ion, but sheÕs not sure
what kind of metal it is. She injects the metal
ions into the hot flame of an atomic emission
spectrometer and observes two line spectra. The
lines correspond to the wavelengths of 563
nanometers (nm) and 615 nm. This combination is the
"fingerprint" for tin. The ecologist may then trace
the tin to a particular type of ship's paint or a
nearby industrial source.
In this lab, you have a little bit easier task than
separating metal ions from sea mud. You are
observing various light sources including tubes
that have been filled with various types of gases.
As electricity passes through these tubes, the gas
glows and light is given off. You will compare the
spectra of these gas tubes with incandescent
(regular light bulb) sources and fluorescent light
fixtures. Specifically, you will be asked to
identify the gas that is used to fill fluorescent
light tubes.
PROCEDURE
- Listen to your teacher's directions on how to
use and care for the Spectrometer. These
instruments are expensive and fragile, so make
certain that you understand the rules for their
use.
- Rotate with your lab partner through the
various observation stations. Use the Spectrometer
placed at each station to take your measurements.
Everyone will start at different stations and move
through the lab to complete their observations in
the time established by the teacher. When observing
the light from a gas tube, make sure that the
center of the glowing spectrum tube is very close
to and directly in front of the spectrometer slit
(CAUTION: Do not touch the gas tubes because they
are hot and may give you an electrical shock! ).
- Incandescent light bulb (white light)
This is a "regular" light bulb. Sketch
what you see on the diagram below,
marking the wavelengths that define each
colored region. Also, mark the limits of
your visual range on both ends of the
spectrum. Sketch the range of colors
observed using the colored pencils, and
note the regions where the colors are
most bright and most dim.
- Hydrogen gas tube
Measure and draw the wavelength of any
line spectra that appear on the blank
spectrum on your data sheet. Sketch the
range of any colors observed using the
colored pencils, and note the regions
where the colors are most bright and most
dim.
- Helium gas tube
Measure and draw the wavelength of any
line spectra that appear on the blank
spectrum on your data sheet. Sketch the
range of any colors observed using the
colored pencils, and note the regions
where the colors are most bright and most
dim.
- Neon gas tube
Measure and draw the wavelength of any
line spectra that appear on the blank
spectrum on your data sheet. Sketch the
range of any colors observed using the
colored pencils, and note the regions
where the colors are most bright and most
dim.
- Mercury gas tube
Measure and draw the wavelength of any
line spectra that appear on the blank
spectrum on your data sheet. Sketch the
range of any colors observed using the
colored pencils, and note the regions
where the colors are most bright and most
dim.
- Nitrogen gas tube
Measure and draw the wavelength of any
line spectra that appear on the blank
spectrum on your data sheet. Sketch the
range of any colors observed using the
colored pencils, and note the regions
where the colors are most bright and most
dim.
- "Plant Grow" light bulb
This is an incandescent bulb that is
supposed to provide more light in the
wavelengths that plants can use than
normal light bulbs. On your data sheet,
sketch what you see, marking the
wavelengths that define each colored
region. Also, mark the limits of your
visual range on both ends of the
spectrum. Sketch the range of any colors
observed using the colored pencils, and
note the regions where the colors are
most bright and most dim.
- Compact Fluorescent light fixture
Because fluorescent lights use
considerably less electricity than
incandescent bulbs, these light fixtures
have been invented so that fluorescent
lights can be screwed into regular light
bulb sockets. They are manufactured in a
different way from regular fluorescent
tubes. Measure and draw the wavelength of
any line spectra that appear on the blank
spectrum on your data sheet. Sketch the
range of any colors observed using the
colored pencils, and note the regions
where the colors are most bright and most
dim.
- Chemical Light Sticks
These light sticks work by a chemical
reaction which releases light energy
instead of heat, sound, or electricity as
other reactions may do. The reaction is
very similar to the one that occurs in
the tails of fireflies! On your data
sheet, sketch what you see, marking the
wavelengths that define each colored
region. Also, mark the limits of your
visual range on both ends of the
spectrum. Sketch the range of any colors
observed using the colored pencils, and
note the regions where the colors are
most bright and most dim.
- Fluorescent light source
Turn your spectrometer slit toward a
standard fluorescent light tube. This
type of lighting is very common in
schools and offices because it uses much
less electricity than traditional
incandescent light bulbs. Measure and
draw the wavelength of any line spectra
that appear on the blank spectrum on your
data sheet. Sketch the range of any
colors observed using the colored
pencils, and note the regions where the
colors are most bright and most
dim.
Complete the following questions.
QUESTIONS
- Helium was discovered in the Sun's corona
during the eclipse of 1868. In 1888,
traces of helium were isolated here on
Earth. How could scientists determine
that this was the same gas that had been
identified on the Sun?
- Compare the results of the various gas tube
spectra with the spectrum observed using
the standard fluorescent light tube.
Based on your results, what gas do you
think is used in fluorescent light tubes?
- Was there any difference between the
spectra of the standard fluorescent light
tube and the compact fluorescent light
fixture? Why do you think this is so?
- Compare the results of the incandescent
light bulb with the spectra of the
fluorescent light tube and the compact
fluorescent light fixture. Based on the
observed spectra, can you think of a
reason why the fluorescent lights are
considered as more "energy efficient"?
Could there be a disadvantage to this?
- Now that you know more about what gases
are contained in fluorescent lights, why
do you think there is a concern about the
breakage and improper disposal of these
tubes?
- What colors dominated the spectrum of the
"Plant Grow" light? How was this
different from the regular light bulb?
Can you think of a reason why this light
might be better for plants (hint: plants
are usually green...)?
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