REMOTE LAB ACTIVITY
SUBJECT SEMESTER: ________________TITLE OF LAB: Emission
SpectroscopyLab format: This lab is a remote lab
activity.Relationship to theory (if appropriate):This activity
covers the relationship between colors and absorbed/emitted light,
as well as the relationship between absorption of electromagnetic
radiation and global warming.Instructions for Instructors: This
protocol is written under an open source CC BY license. You may use
the procedure as is or modify as necessary for your class. Be sure
to let your students know if they should complete optional
exercises in this lab procedure as lab technicians will not know if
you want your students to complete optional exercise.Instructions
for Students: : Read the complete laboratory procedure before
coming to lab. Under the experimental sections, complete all
pre-lab materials before logging on to the remote lab, complete
data collection sections during your on-line period, and answer
questions in analysis sections after your on-line period. Your
instructor will let you know if you are required to complete any
optional exercises in this lab.Remote Resources: UV/Vis
Spectrometer; Secondary - Emission Tubes.CONTENTS FOR THIS NANSLO
LAB ACTIVITY:Learning Objectives 2Background Information 2 -
3Equipment 3Pre-lab Assignment 3 - 4Experimental Procedure 4
5Analysis (Can Be Done Offline If Necessary) 5 - 7Preparing to Use
the Remote Web-based Science Lab (RWSL) 8 - 19
LEARNING OBJECTIVES:1. Identify the most intense peaks in the
emission spectra for several molecular and atomic gases.2. Use the
visible emission spectrum for hydrogen gas to determine the
electronic transitions taking place and compare these with the
theoretical predictions using the Rydberg equation.3. Relate
wavelength and color of light.4. Calculate frequency and energy of
electromagnetic radiation from its known wavelength.5. Predict
absorption of light by a gas from its emission spectrum.6. Identify
an unknown gas by its emission spectrum.BACKGROUND
INFORMATION:Spectroscopy is the study of the interaction between
light and matter, in particular how atoms or molecules absorb or
emit electromagnetic (EM) radiation. Electromagnetic radiation is
characterized by its wavelength or its frequency, which are related
by the equation c = , where is wavelength (typically units are
nanometers for visible light), is frequency (units are s-1, known
as Hertz or Hz) and c is the speed of light (299,792,458 m/s). Note
that for any wave, its wavelength times its frequency equals its
speed; for electromagnetic radiation that speed is the speed of
light. Also note that as wavelength increases, frequency decreases,
and vice versa.
Electromagnetic radiation may be understood as having both
wave-like and particle-like properties, depending on the
experimental setup and the type of detector used (in this
experiment, we are measuring wavelengths using a spectrometer that
emphasizes the wave-like properties of light). From a particle-like
point of view, the smallest amount of EM radiation (of a particular
wavelength) that can be emitted or observed is called a photon. As
Albert Einstein showed more than a century ago, the energy of a
photon is proportional to the frequency of the EM radiation
involved (and thus inversely proportional to the wavelength):
Ephoton = h, where h is called Plancks constant (h = 6.62607 x
10-34 Js). Since energy is conserved and since atoms and molecules
almost always emit or absorb one photon at a time, the change in
energy of an atom or molecule will determine the frequency (and
wavelength) of the EM radiation absorbed or emitted: Eatom =
Ephoton = h = hc / .
Atoms (or molecules) emit photons of very distinctive wavelength
(as determined by the previous equation) when the energy of the
atom decreases. Atoms can absorb energy when they absorb a photon
with an appropriate wavelength (a photon whose energy matches the
difference in energy between the initial and final energy states of
the atom, Eatom). Since atoms have quantized energy levels (only
certain energy levels are possible,) there are only certain values
possible for Eatom. Thus, only certain frequencies and wavelengths
of EM radiation will be emitted by the atoms (and molecules) in
this experiment.
For most atoms, determining the energy levels possible involves
very complex quantum mechanical calculations. The H atom (hydrogen)
is a notable exception since it is the simplest of atom with only a
single electron. Even before quantum mechanics was discovered and
understood, physicists and chemists were able to write a very
simple equation to predict the wavelengths for the EM radiation
absorbed or emitted by H atoms known as the Rydberg equation: 1 / =
RH {(1/n12) (1/ n22)} where RH is called the Rydberg constant
(0.010967760 nm-1), and n1 and n2 are positive (non-zero) integers
called quantum numbers such that n1 < n2. See your text for more
details about the Rydberg equation and to see an example of using
this equation in a calculation.
You may notice that we are using hydrogen molecules (H2) in this
experiment whereas the Rydberg equation only applies to hydrogen
atoms (H). Hydrogen atoms are not chemically stable, but H2
molecules are stable and can be used to fill the glass tube in the
hydrogen lamp. The high-voltage electrical discharge used to power
the lamp will temporarily break up H2 molecule into individual H
atoms which then gain additional energy from the discharge. This
additional energy is then emitted in the form of visible light as
the H atoms return to lower energy states.The energy of a photon of
electromagnetic radiation is given by the relationship: E = h where
E = energy in joules, = frequency in cycles per second, and h =
Plancks constant = 6.62607 x 10-34 JsThe relationship between
wavelength and frequency of electromagnetic radiation is: = c where
= wavelength in meter and c = 2.996 x 108 m/s, the speed of radiant
energy in a vacuum
EQUIPMENT: Paper Pencil/Pen Computer with Internet access
PRE-LAB ASSIGNMENT:1. Use the Rydberg equation to predict the
wavelength of the electromagnetic radiation emitted for following
electron transitions for the hydrogen atom (rounded-off to the
nearest 0.1 nm).
2. Using Figure 1 and your predicted wavelengths above,
determine what type of electromagnetic radiation is produced by
these electron transitions in the hydrogen atom. In other words,
does the transition of n = 3 2 produce ultraviolet (UV), visible or
infrared (IR) radiation? What about the other transitions
above?
Figure 1: By Jonathan S. Urie [CC-BY-SA-3.0
(http://creativecommons.org/licenses/by-sa/3.0)] via Wikimedia
Commons
3. Review the Experimental Procedure below and let your
instructor know if you have any questions.EXPERIMENTAL
PROCEDURE:Read and understand these instructions BEFORE starting
the actual lab procedure and collecting data. Feel free to play
around a little bit and explore the capabilities of the equipment
before you start the actual procedure.Once you have logged on to
the Remote Lab, you will perform the following Laboratory
procedures:4. Use the control panel to gather data from the
emission lamps.
a. Be sure to start the spectrometer so you can view the spectra
when the lamps are energized.b. Use the camera to zoom in on each
emission lamp to read the labels and determine what gas is in each
one.c. Use the screw-drive robot to position the fiber optic cable
for the spectrometer and record the spectrum of each of the
emission lamps. d. While viewing each spectrum, use the cursor to
find the wavelength of five or six most intense peaks for each of
the gases. Record these in a table.e. Also, while each lamp is
glowing, zoom in close with the camera and see what color it
appears to be.ANALYSIS (CAN BE DONE OFFLINE IF NECESSARY):5. How
closely do the first three transitions listed in the table you
prepared in the pre-lab assignment correspond to the observed
wavelength of the three largest peaks in the hydrogen atom emission
spectrum?
6. Note that all the most intense peaks for neon gas have
wavelengths greater than 580 nm. Based on Figure 2, what colors of
visible light are emitted by the neon tube? Does this explain the
apparent color of neon lamps to the naked eye?
Figure 2: Visible Portion of EM Spectrum7. Shown below is a
portion of the emission spectrum produced by a mixture of two of
the gases involved in this experiment. Based on your experimental
results, does this gas mixture include helium gas? Explain your
reasoning. Can you determine which two gases are in this gas
mixture?
Figure 3: Spectrum of Gas Mixture
8. Iron vapor produces an emission spectrum that includes an
intense peak at 527.0 nm. Determine the frequency (in Hz) for this
type of electromagnetic radiation. What color of visible light
corresponds to this wavelength? What is the energy (in J) per
photon emitted at this wavelength? What is this photon energy in
units of kJ per mole? (In other words, one mole of these photons
with wavelength of 527.0 nm consists of how many kilojoules of
electromagnetic energy?)
9. The peaks that you observe in the emission spectrum of each
gas are also wavelengths of light that the gas will absorb better
than others. So, if a gas shows an emission peak at 550 nm, the gas
will also absorb light with a wavelength of 550 nm. The more
intense the emission peak, the more that light will be absorbed by
the gas. Based on this information, rank the four gases you
observed in this experiment in order of how well they will absorb
infrared light. Write the strongest infrared absorber on the left
and the weakest on the right:
Best absorber > next best > next best > worst
absorber10. Based on these results, and the reference listed below,
why do you think carbon dioxide is considered a greenhouse gas that
we need to be concerned about when compared to the other gases you
observed in this experiment?
Reference:
http://www.ecoearth.org/article/Atmospheric_composition
(Bear in mind that these results only take a small portion of
the infrared portion of the spectrum into account.)
11. Figure 4 below shows the absorption spectra of several
common gases that are prevalent in the atmosphere. Peaks in this
spectrum indicate the wavelengths that these gases absorb the best.
The horizontal axis is the wavelength in microns which is another
name for micrometers. Note that this horizontal axis is a
logarithmic axis. So this single figure covers a large portion of
the electromagnetic spectrum, namely the ultraviolet, visible and
infrared regions of the spectrum. The vertical axis is the percent
absorptivity of each gas (in other words, what percent of EM
radiation at a given wavelength is absorbed by each gas). A percent
absorptivity of zero means a gas is completely transparent at that
wavelength. A value of 100 means complete absorbance at that
wavelength so the gas is opaque. The spectrum labeled "Total"
corresponds to the spectrum of the total atmosphere.
a. The visible spectrum is typically defined as wavelengths
between 400 and 700 nm. Convert these wavelength values to microns
and locate the visible region in the figure below. Also locate the
ultraviolet and infrared regions of the figure (hint: does infrared
radiation have longer or shorter wavelengths than visible light?).
b. Does the spectrum labeled "Total" indicate whether the
atmosphere is mostly transparent or mostly opaque in the visible
region? Briefly explain your answer.c. The figure also shows that
the Earth emits large amounts of thermal radiation at wavelengths
between about 5 and 50 microns. Is this in the ultraviolet,
visible, or infrared region of the spectrum? Greenhouse gases can
cause global warming by absorbing this emitted thermal radiation,
trapping heat in the Earths atmosphere. Are carbon dioxide, water
or oxygen (plus a little ozone, O3) greenhouse gases according to
this figure? Briefly explain your answer. d. Why are scientists and
governments much more concerned about carbon dioxide acting as a
greenhouse gas than water or oxygen? What effect do human
activities have on the levels of these gases in the atmosphere?
Figure 4: Solar Radiation12. Identify the unknown gas in the
emission lamp labeled E. Explain why you think you are correct.
PREPARING TO USE THE REMOTE WEB-BASED SCIENCE LAB (RWSL):Read
and understand the information below before you proceed with the
lab!Scheduling an Appointment Using the NANSLO Scheduling
SystemYour instructor has reserved a block of time through the
NANSLO Scheduling System for you to complete this activity. For
more information on how to set up a time to access this NANSLO lab
activity, see www.wiche.edu/nanslo/scheduling-software. Students
Accessing a NANSLO Lab Activity for the First TimeYou must install
software on your computer before accessing a NANSLO lab activity
for the first time. Use this link to access instructions on how to
install this software based on the NANSLO lab listed below that you
will use to access your lab activity
www.wiche.edu/nanslo/lab-tutorials.1. NANSLO Colorado Node -- all
Colorado colleges. 2. NANSLO Montana Node -- Great Falls College
Montana State University, Flathead Valley Community College, Lake
Area Technical Institute, and Laramie County Community College. 3.
NANSLO British Columbia Node -- Kodiak College.Using the
Spectrometer for the Emission Spectroscopy NANSLO Lab ActivityWe've
provided you with three ways to learn how to use the microscope for
this NANSLO lab activity:1. Read these instructions. 2. View this
short video at
https://www.youtube.com/watch?feature=player_embedded&v=X8Mr1nuVm3Y.
SPECTROMETER LAB INTERFACE INSTRUCTIONSThe Remote Web-based Science
Lab (RWSL) spectrometer is controlled remotely by using a web
interface as shown below. This lab interface allows you to control
every function of the spectrometer just as if you were sitting in
front of it.The equipment control software shown below is written
using the LabVIEW software from National Instruments. The user
interface is presented as a LabVIEW control panel which will be
referred to as the lab interface for the remainder of the
document.Figure 5: Spectrometer lab interface for emission
spectroscopy labCOMMUNICATING WITH YOUR LAB PARTNERSAs soon as you
have accessed this lab interface, call into the toll free
conference number shown on the control panel to communicate with
your lab partners and with the Lab Technicians. Use the PIN code
noted to join your lab partners. Only one person can be in control
of the equipment at any one time so talking together on a
conference line helps to coordinate control of the equipment and
creates a more collaborative environment for you and your lab
partners.GAINING CONTROL OF THE SPECTROMETERRight click anywhere in
the grey area of the lab interface and choose Request Control of VI
from the dialogue box that appears when multiple students are using
the spectrometer at the same time,. After you request control, you
may have to wait a short time before you actually receive control
and are able to use the features on this lab interface.
Figure 6: Take control of the lab interface by right clicking
and selecting "Request Control of VI."RELEASING CONTROL OF THE
SPECTROMETERTo release control of the spectrometer so that another
student can use it, right click anywhere in the grey area of the
lab interface and choose "Release Control of VI" from the dialogue
box that appears.
Figure 7: Release control of the lab interface by right clicking
and selecting "Release Control of VI."ACTIVATING THE SPECTROMETERTo
activate the spectrometer, click the "Start" button on the far left
portion of the lab interface. The button will now turn yellow and
say Pause.
Figure 8: After clicking on the "Start" button, it turns to a
"Pause" button.SPECTROMETER VIEW WINDOWThe Image view Window
displays the real-time video feed from a digital camera focused on
the spectrometer, the emission lamps, and a horizontal screw-drive
robot with mounted fiber optic cable located in front of the
emission lamps. The four black boxes, labeled A through E and also
labeled from left to right H2, He, Ne, CO2 and ?, are the emission
lamps that generate different colors of visible light depending on
the gas that is in them. The optic cable transmits the detected
light to the spectrometer where the spectrum is digitally acquired.
The spectrometer is the small box located near one end of the
track.
Figure 9: Spectrometer View Window showing spectrometer,
emission lamps, and robot with mounted optic fiber.CAMERA PRESETS
AND PAN-TILT-ZOOM CONTROLSSeveral camera preset positions have been
programmed for use with this lab interface. Hovering over the grey
area where the buttons are will give you a pop-up menu that
describes where each preset is assigned to as shown in Figure 10.
Camera presets 1 through 5 allow you to zoom in quickly to one of
the 5 lamps. Preset Camera 6 allows you to see a full view of the
spectrometer, the emission lamps, and a horizontal screw-drive
robot with mounted fiber optic cable located in front of the
emission lamps.
Figure 10: Six camera presets.The four arrows used to pan and
tilt allow you to move the camera right to left and up and down.
The two zoom buttons allow you to zoom in to see a closer look at
the equipment such as shown in Figure 11 or zoom out to view more
of the room.
Figure 11: Pan, tilt and zoom capabilities.SETTING UP THE
SPECTROMETERTo acquire the spectrum of one of the emission lamps,
first select Camera Present 6 - Full View so that you can see the
sensor move along the track. Click on the green-colored A button on
the left side of the screen. This will position the sensor in front
of this tube and turn on the H2 emission lamp.
Figure 12: Select Camera Present 6 and the "A" button.Next click
on Camera Preset 1 to view a closeup of the H2 emission lamp once
it is turned on.Use the Nudge Left and Nudge Right buttons to move
the fiber optic and make sure you are getting the maximum signal
from the lamp. If the lamp turns off before you are finished, just
click the same letter again, and it will re-energize. By default,
the TimeTubeOn is set to 60 seconds. You can adjust this setting;
however, because of the high voltage involved in these lamps, DO
NOT set the TimeTubeON field to more than 120 seconds. The lamp
status and the number of seconds it has been energized are shown in
the Lamp Status portion of the interface screen (to the right of
the green lamp buttons A E).Once you have the signal maximized,
click the Pause button to hold the image so the light doesnt have
to be energized while you locate the maximum peaks (Figure 13).
Figure 13: Press the Pause button to "freeze" the spectrumYou
will now need to zoom out on the spectrum window to view the entire
spectrum properly. Heres how to zoom in and out on the spectrum:1.
Click on the center button at the lower right of the graph, shown
below in Figure 14.
Figure 14: Click button to access other options.2. This brings
up a small sub-menu of other buttons. The only two that are useful
to you are the left-most buttons in the top and bottom rows. Select
the left-most button in the bottom row to view the entire
spectrum.
Figure 15: Spectrum Zoom Out Button3. Select the left-most
button in the top row to select specific parts of the spectrum to
zoom in on and view more closely (see Figure 16). After clicking
this button, you use the mouse to draw a box around the area that
you want to zoom in to. Be sure you draw the box so that it
includes some area past the top of the peak you are interested in
or else it will chop off the top of it in the viewing window. If
you accidentally zoom in too far or on the wrong part of the
spectrum, just zoom out and start over again.
Figure 16: Spectrum Zoom In ButtonIDENTIFYING THE PEAK TO
EXPORTTo export a graph, you will first locate the most intense
peaks. Make sure you are zoomed out to view the entire spectrum
(Figure 15 above.) Click the button labeled "Enable Cursor" under
the left side of the graph. The green light will come on, and a
vertical green cursor line will appear on the screen. Click the
cursor control button. Use the mouse to "grab" the cursor line by
clicking on it and dragging it to the peak that you want to
identify. You must have control of the lab interface to be able to
do this activity.
Figure 17: Click the "Enable Cursor" button and then the "Cursor
Control" icon to identify the peak.There are now two fields under
the graph: Wavelength (nm) and Intensity. The Wavelength field
shows the current position of the cursor, and Intensity shows a
relative intensity reading of wherever the cursor is located
(Figure 17).
Use the cursor to find the wavelength of each major peak in the
spectrum.
Once you have the cursor on top of a peak, you can zoom in on it
to make sure you are really on the highest part of the peak.
(Sometimes they are double peaks!) If you zoom in or out, you will
need to click the cursor control button again in order to move the
cursor.If you want to zoom in on a peak for a closer look, make
sure you place the cursor approximately on that peak before you
click the "Spectrum Zoom In" button and draw a bar around it.If you
lose the cursor while zooming in on peaks, just zoom out again to
find it.EXPORTING A GRAPH OF THE SPECTRUMLocate the" Export to
Clipboard" button. Go to the pull-down box to the right of it and
set it to "Graph Image." Now click the Export to Clipboard button
which will place a copy of the spectrum in your clipboard.
Start a program like Paint or Word or PowerPoint and paste in
the spectrum. Save the file with an appropriate name so you can
find it later.You must have control of the Control Panel to do
this, of course.For more information about NANSLO, visit
www.wiche.edu/nanslo.All material produced subject to:
Creative Commons Attribution 3.0 United States License 3
This product was funded by a grant awarded by the U.S.
Department of Labors Employment and Training Administration. The
product was created by the grantee and does not necessarily reflect
the official position of the U.S. Department of Labor. The
Department of Labor makes no guarantees, warranties, or assurances
of any kind, express or implied, with respect to such information,
including any information on linked sites and including, but not
limited to, accuracy of the information or its completeness,
timeliness, usefulness, adequacy, continued availability, or
ownership.
19 | PageLast Updated May 5, 2014