Name _________________________________________________
Date
Initials
Minutes
Score
Investigation 2: Electron Arrangement
Pre-Lab 2A
5
POINTS
1. Go to the Chemistry Lab page:
http://www.redjacket.org/webpages/ottr/chemistry.cfm
2. Complete and submit the questions before the next lab class.
3. Read Diffraction Gratings.
Materials:
Name
Barium nitrate
5
POINTS
Formula
Safety Information
Calcium nitrate
Copper (II) nitrate
Hydrochloric Acid
Lithium nitrate
Lead nitrate
Potassium nitrate
Sodium nitrate
Strontium nitrate
Regents Chemistry Lab  Page 19
Diffraction Gratings
Introduction:
A diffraction grating is made by making many parallel, closely spaced scratches on the
surface of a flat piece of transparent material. The scratches are opaque but the areas
between the scratches can transmit light. The multitude of parallel slits split and diffracts
the light. Like a prism, a diffraction grating separates the colors in white light to produce
a spectrum. The spectrum, however, arises not from refraction but from the diffraction of
the light transmitted or reflected by the narrow lines in the grating.
Procedure:
1. Obtain a diffraction grating. Handle it by the frame only. Do not scratch the surface.
2. Turn off the classroom lights and view the spectrum of an incandescent light.
Through the diffraction grating. Is the spectrum continuous? Concentrate at the red
and violet ends of the spectrum. Do you see more red or more violet?
3. Turn on the lights. Hold the diffraction grating toward the fluorescent lights. Is the
spectrum continuous? Do you see more red or more violet?
4. Compare two fabric swatches under both types of light and complete the table. Does
swatch #1 appear more maroon or red? Does swatch #2 appear more blue or purple?
Results:
5
POINTS
White Light
Incandescent
Continuous
Red or Violet
Swatch #1
Fluorescent
Pre-Lab 2B
5
POINTS
1. Go to the Chemistry Lab page:
http://www.redjacket.org/webpages/ottr/chemistry.cfm
2. Complete and submit the questions before the next lab class.
3. Read Emission Spectra.
Investigation 2  Page 20
Swatch #2
Emission Spectra
Introduction:
A quantum leap is a change of an electron from one quantum state to another within an
atom. The electron "jumps" from one energy level to another very quickly, after existing
briefly in a state of superposition. The normal electron configuration of atoms or ions of
an element is known as the “ground state” when electrons are in the lowest energy levels
available. When electrons absorb enough energy and “leap” to higher energy levels the
element is said to be in the “excited state”. One convenient method of exciting the atoms
of an element is to pass an electric current through a sample of the element in the gaseous
phase (see Fig.1). This is the principle behind the spectrum tubes we will be using in this
investigation. Each tube contains a small amount of vapor. The electric discharge through
the tube will cause the vapor to glow brightly. The glow is produced when excited
electrons emit radiant energy as they return to lower energy levels. When this visible
radiant energy is passed through a diffraction grating, an emission spectrum (or brightline spectrum) is produced, dispersing the photons of various wavelengths (colors)
contained in the beam of light.
Figure 1
Procedure/Results:
5. Turn on the transformer with the hydrogen gas sample. Describe the sample of H2.
6. Using colored pencils diagram the visible bright-line spectra of H2 to scale.
5
POINTS
Regents Chemistry Lab  Page 21
7. Compare this bright line spectrum to a continuous spectrum.
8. With the transformer off and the power cord unplugged, carefully replace the tube
with helium gas. Describe the electrified sample of He.
9. Using colored pencils sketch the visible bright-line spectra of He.
5
POINTS
10. Repeat step 3, but replace the tube with neon gas. Describe the sample of Ne.
11. Using colored pencils sketch the visible bright-line spectra of Ne.
12. Repeat step 3, but replace the tube with oxygen gas. Describe the sample of O2.
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POINTS
13. Using colored pencils sketch the visible bright-line spectra of O2 .
Investigation 2  Page 22
Explanation:
5
POINTS
1. What is the relationship between the observed color of each tube without using the
diffraction grating and the multiple colors of the bright line spectra observed using
the diffraction grating?
2. Write electron configurations for each of the gases tested.
Element
Electron
Configuration
Pre-Lab 2C
5
POINTS
1. Go to the Chemistry Lab page:
http://www.redjacket.org/webpages/ottr/chemistry.cfm
2. Complete and submit the questions before the next lab class.
3. Read Energy Levels.
Energy Levels
Introduction:
Each electron in an atom has its own distinct amount of energy that corresponds to the
energy level it occupies. Electrons can gain and lose energy and move from one discrete
energy level to another. Energy levels (n) may be = 1,2,3,…
In this investigation we will study the emission spectra of hydrogen (which has only one
electron) Most wavelengths from this spectra are beyond our visible range so we will
only view wavelengths associated with specific spectral lines in the Balmer series that
result when electrons in shells n > 2 transition to n = 2.
Each wavelength can be mathematically related to a definite quantity of energy produced
by the movement of electrons from higher energy levels to lower energy levels. Thus
emission spectra are experimental proof that electrons exist at definite, distinctive energy
levels in an atom.
Regents Chemistry Lab  Page 23
Procedure:
1. Set up the apparatus as shown in Figure 2. The slit should be placed on the 50.0 cm
mark of one-meter stick. The high-voltage transformer with spectrum tube should be
placed directly behind the screen so the light is transmitted through the slit. The
diffraction grating should be placed on the second meter stick at exactly 100.0 cm.
Plug in and turn on the transformer.
Figure 2
2. One observer will view the emission spectrum of hydrogen by looking through the
diffraction grating at the slit in the cardboard screen. Another student will move a
pointer slowly along the meter stick nearest the transformer. The student viewing the
spectrum should indicate when the pointer is superimposed over the image of the
spectral line.
3. Measure the distance, in centimeters, between the tube and the image of the spectral
line. Record this distance (x) in the data table.
4. Repeat step 3 for the other spectral lines of hydrogen.
5. Disconnect the transformer.
Results:
Bright-line
x (cm)
5
POINTS
Investigation 2  Page 24
y (cm)
Calculation:
Calculate and tabulate the following for hydrogen. Show your work for one of each
calculation and record the answers in the table below.
1. Find the hypotenuse (z) from the diffraction grating to the image of the spectral line.
(x2 + y2 )
z =
5
POINTS
2.  is the angle of emergence of the spectral line through the diffraction grating. Find
the sine of  (N.B. Remember from trigonometry that the sine of an angle is opposite
over hypotenuse.)
sin =
x
/z
3. Find the slit separation (d) on the diffraction grating we used from N, the grating
constant. N is simply the number of scratches per cm in the diffraction grating.
d =
1
/N
4. From the sine of the angle and slit separation find the wavelength () of the spectral
line.
5
POINTS
 = d (sin)
5. Convert the wavelength from centimeters to Angstroms.

(in Angstroms) =  (in cm) x 108 Å/ cm
Bright-line
z (cm)
sin 
 (cm)
 (Å)
% error
5
POINTS
Regents Chemistry Lab  Page 25
Error Analysis:
1. These visible colors produced by hydrogen are from
the Balmer series. Calculate percent error to compare
your experimental results to the known wavelengths
listed in Angstroms. Show your work for one
calculation and record the answers in the table above.
Bright-line
Red
Blue-green
Blue
Violet
 (in Å)
6564
4862
4341
4102
Explanation:
1. From your investigation what is the relationship between the wavelength and color in
the visible spectrum.
5
POINTS
2. Research and find which colors of light have more energy.
3. Based on your answers above, predict and explain whether light with longer or
shorter wavelengths should have greater energy.
5
POINTS
Investigation 2  Page 26
4. Based on your answers above, predict and explain which bright-line color from the
Balmer series is produced in the Bohr model of the atom below showing a transition
from n = 5 to n = 2.
Pre-Lab 2D
5
POINTS
1. Go to the Chemistry Lab page:
http://www.redjacket.org/webpages/ottr/chemistry.cfm
2. Complete and submit the questions before the next lab class.
3. Read Flame Tests.
Flame Tests
Introduction:
We have used electricity in the previous activities to excite electrons. When atoms or
ions in the ground state are heated to a high temperature electrons can be excited. As
always, the excited condition is unstable, and the electrons “fall” to their normal levels of
lower energy. As the electrons return to the ground state, the energy that was absorbed is
emitted in the form of electromagnetic radiation.
In this activity we will record the flame test color of several salts by placing solutions of
the salts with a wire loop into a Bunsen burner flame. Only metals, with their loosely held
electrons, are excited easily in the flame of the laboratory burner. Thus, flame tests are
useful in the identification of metallic cations (positively charged ions). Many cations
exhibit characteristic colors when vaporized in the burner flame. In this experiment,
characteristic colors of several different metals will be observed. After your tests, you
will be given a numbered, unknown solution, which you will attempt to identify.
Regents Chemistry Lab  Page 27
Procedure/Results:
Safety glasses are required for all of the following procedure.
1. Obtain, rinse with deionized water, and dry a well plate. Place a few drops of 1.0 M
HCl into each of five wells in the well plate.
2. Clean a wire loop under water and then with steel wool.
3. Dip the flame test wire into the first well of HCl, and then hold it in the flame for 10
seconds. Place the wire into the second well of HCl then into the flame for 10
seconds. Repeat the process in the 3rd, 4th, and 5th well of HCl.
4. Place a few drops of a test solution into an empty well. You will be testing salts of
barium, calcium, copper, lead, lithium, potassium, sodium, and strontium in any
order.
5. Dip the wire into the well to capture a droplet of solution then place the loop in the
flame. Repeat this step until you are confident of the color. Record your results.
6. Repeat procedures 2 through 5 for each of the test solutions.
5
POINTS
Cation
Color
7. Using clean spoons place a few crystals of each of the following solids in three
separate wells, sodium nitrate, potassium nitrate, and a mixture of the two.
8. Obtain a filter paper. Handle it by the edges. Rip the paper in half; do not touch the
center of the uneven edge. Rip each semicircle in half; again do not touch the uneven
edges. You should have four quarters of filter paper, each with a clean point.
Investigation 2  Page 28
9. Liberally wet the point on a quarter of filter paper with deionized water. Dip the
moistened point into one solid nitrate sample. Place the point of the paper in the edge
of a Bunsen burner flame. CAUTION: Do not leave the filter paper in the flame
for more than 5 seconds to prevent burning. If the filter paper does begin to
burn immediately place it in a beaker of tap water.
10. Record the color. Repeat with new filter paper points for each of the three samples.
11. Repeat step 10, but observe the flames through two thicknesses of cobalt glass.
Record the color as seen through the glass.
Cation
Color without Co Glass
Color through Co glass
5
POINTS
Explanation:
1. Compare flame tests to spectral lines.
2. Discuss the use of cobalt glass as a light filter.
Regents Chemistry Lab  Page 29
3. Write the electron configuration and determine the number of valence electrons for
each sample tested.
5
POINTS
Sample
Ba
Electron Configuration
Valence Electrons
Ca
Cu
Li
Pb
K
Na
Sr
Unknown Cation Determination
Introduction:
Each element has its own unique emission spectrum by which it can be identified. Using
flame tests the color light produced can be used to identify the elements involved. You
will use your results to identify a metal in unknown salt solutions. This process is the
same as that used by chemical laboratories to identify the make-up of chemical
contamination in chemical spills, landfills, industrial sites, etc.
Procedure:
Safety glasses are required for all of the following procedure.
1. Each lab partner should obtain a sample of unknown salt solution. Record their
numbers. Perform a flame test and record the color. The unknown sample can be
identified by comparing its color to those salts previously tested.
Investigation 2  Page 30
Results:
Error Analysis:
5
POINTS
Discuss sources of error from the procedural method or experimental set up that may
cause uncertainty in your determination.
Regents Chemistry Lab  Page 31
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Investigation 2  Page 32