REGENTS CHEMISTRY LAB
SPECTROSCOPIC STUDY OF ELEMENTS
Introduction:
When electrical energy is directed through gas tubes containing elements, we see that each
element creates a different colored light. This is the principle behind “neon” lights used for
advertising. When the light from a glowing gas is passed through a diffraction grating or
spectroscope, you will see that a particular color seen with your eyes is really a series of
colored “bright lines” all blended together.
In this lab you will observe the emitted light emitted from several gas discharge tubes using a
spectroscope. When you view the light from the glowing gas, it will be broken up into
several brightly colored lines called “spectral lines”. Each spectral line indicates excited
electrons that are falling back down to the ground state and emitting photons of energy of
specific wavelengths. You will be able to read the wavelengths (in angstroms) of each
brightly colored line.
From the observed wavelengths, you will calculate the frequency and energy of each bright
line (for hydrogen only). You will then compare your data to a chart to determine which
electron jump is responsible for each colored line for hydrogen These calculations will be
done for hydrogen gas only.
‫ ٭‬Precautions:
Turn off the spectrum tubes as soon as you are done using them. Letting
them constantly burn reduces their useful life span.
DO NOT touch black power supplies.
Procedure:
1.
Using the gas discharge tubes note the colored lines that you see through a
spectroscope and record the color and wavelengths (in Å) for each bright line.
Record wavelengths for the following tubes on the attach data sheet
Hydrogen
Mercury
Helium
Neon
Air
Sodium
Oxygen
Water
Fluorescent light bulb (look for the bright lines within the “rainbow”)
Calculations and Questions:
1.)
For the hydrogen tube only, calculate the energy of each bright line that you observed.
Red Line:
Wavelength converted to meters (1 Angstrom = 1x10-10 meters)
Determine the frequency of the colored line using this formula:
c = speed of light = 3 x 108 meters/sec
λ = wavelength (in meters) of the colored line
γ = frequency (in cycles/sec) of the colored line
Determine the energy of the colored line using this formula:
γ = frequency (in cycles/sec) of the colored line
E = energy in Joules
h = Planck’s constant = 6.63 x 10-23 J/sec
Frequency (γ):_____________________
Energy (E): _______________________
Determine the frequency of the colored line using this formula:
c = speed of light = 3 x 108 meters/sec
λ = wavelength (in meters) of the colored line
γ = frequency (in cycles/sec) of the colored line
Wavelength (λ): ___________________
c = λ x γ
Frequency (γ):_____________________
E = h x γ
Energy (E): _______________________
Purple Line:
Wavelength converted to meters (1 Angstrom = 1x10-10 meters)
Determine the frequency of the colored line using this formula:
c = speed of light = 3 x 108 meters/sec
λ = wavelength (in meters) of the colored line
γ = frequency (in cycles/sec) of the colored line
Determine the energy of the colored line using this formula:
γ = frequency (in cycles/sec) of the colored line
E = energy in Joules
h = Planck’s constant = 6.63 x 10-23 J/sec
c = λ x γ
E = h x γ
Blue Line:
Wavelength converted to meters (1 Angstrom = 1x10-10 meters)
Determine the energy of the colored line using this formula:
γ = frequency (in cycles/sec) of the colored line
E = energy in Joules
h = Planck’s constant = 6.63 x 10-23 J/sec
Wavelength (λ): ___________________
Wavelength (λ): ___________________
c = λ x γ
Frequency (γ):_____________________
E = h x γ
Energy (E): _______________________
2
Compare your answers with this chart, which represents the energy released when an electron in hydrogen
falls between different energy levels and emits energy.
From level 2 to level 1
1.63 x 10-18 J
From level 3 to level 1
1.94 x 10-18 J
From level 4 to level 1
2.04 x 10-18 J
From level 5 to level 1
2.09 x 10-18 J
From level 3 to level 2
3.03 x 10-19 J
From level 4 to level 2
4.09 x 10-19 J
From level 5 to level 2
4.58 x 10-19 J
From level 4 to level 3
1.06 x 10-19 J
From level 5 to level 3
1.55 x 10-19 J
From level 5 to level 4
4.09 x 10-20 J
2.
Using your answers, predict which electron jump is responsible for each colored line in the hydrogen
spectrum. (Example: The red line is caused by an electron jumping from level 5 to level 2, etc.)
3.
Did any similarities exist between the hydrogen, oxygen and water spectrum tubes? Should you
expect any similarities between these three tubes? Why or why not?
4.
The fluorescent tube contains one element whose spectrum you observed in this experiment. By
comparing bright lines and wavelengths of the fluorescent tube with the other spectrum tubes, what
element exists inside a fluorescent light bulb?
5.
Based on the things you have seen in this spectral tube lab, would you expect to see any similarities
between the bright lines in a nitrogen spectrum tube and the bright lines in an air spectrum tube? Why
or why not?
6.
Using the terms excited state, ground state, absorption and emission of energy describe how electrons
cause specific spectral lines according to the Bohr model.
7.
Explain in terms of subatomic particles, why an excited atom is electrically neutral
8.
Describe why emission spectroscopy is a helpful tool in determining the identity of materials in fields
like forensic science.
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