SPECTROSCOPY LAB

A LOOK AT ABSORBTION, CONTINUOUS EMISSION,

AND ATOMIC LINE SPECTRA.

 

(Modified from E-Chem; Thompson, Resseguie; 1994; pgs 21 - 27 and

Chemtrek; Thompson, pgs 12 - 37)

 

Purpose: 

·        To compare various spectra using a spectroscope.

·        To quantitatively measure wavelengths in the visual spectrum.

·        To better understand the uses of spectroscopy.

·        To identify unknown substances by their spectra.

 

Discussion:

                        "A tremendous amount of useful information can be obtained from the analysis of the interaction of light with matter.  The study of the chemical and physical process of the absorbtion and emission of light has proved important in topics as diverse as urine analysis, cosmological chemistry, and interior decorating.  The development of modern theories of color space has provided a sound basis for the extensive use of color in television, computer applications, paints, fabrics, papers and construction materials.  The science of spectroscopy, the analysis of light into its component colors, has revealed the electronic and nuclear structure of atoms and molecules as well as the nature of stars, galaxies, quasars and interstellar matter." (E-Chem, pg 21)  In this lab you will be using your high tech spectrometer to investigate many types of spectra including absorbtion, continuous emission, and atomic line spectra.

 

                        Emission spectra are produced when electrons from the light source lose energy by moving from a higher quantum level to a lower one - emitting that energy in the form of light.  Absorbtion spectra are seen as dark lines (from the spectrum of the sun, called Fraunhofer lines) created by atoms in the sun absorbing energy at specific quantum levels or specific wavelengths.  Electrons move from a lower energy state to a higher one.

 

Procedure:

 

            Part 1: Compare various continuous emission sources.

 

·        Look at the spectra from the following light sources:

                                    Candle, light bulb, Fluorescent light, sun (DO NOT LOOK AT THE SUN!!!, the sky will do.)

·        Record your observations.  Draw pictures to illustrate the differences between spectra.

·        Compare and contrast the different spectra

 

 

            Part 2: Atomic line spectra (emission spectra)

 

There are several discharge tubes available for study.  Each one produces a different line spectra (because they have different gases in them) exclusively its own, a spectral  "finger print".  These "finger prints" are used as an identification tool.

 

·        Be very careful when near discharge tubes, they are very fragile and expensive and the power supply may give you a substantial electric shock!

 

·        Observe the spectra.  Due to the low light level of the tubes, you will get better results if all other lights are off. 

 

·        List each tube you viewed, A, B, C, D, and E, the number of lines visible, the color of each line, and the wavelength of each line by drawing spectra below.

·        Determine the element in the tube by comparing your results with the chart on the wall – known spectra. Hint:  you must know the wavelengths because the chart is based on wavelengths NOT what your spectra look like in your spectroscope.  In addition, due to error, some spectra may not appear to match – do your best!

 

 

Record observations here:  Draw the spectra using rulers and colored pencils or markers.  Superimpose the ruler of the spectroscope on the drawing of your spectra – this will be important for identifying unknowns. 

  1. Candlelight:

 

 

 

 

 

 

  1. Lightbulb:

 

 

 

 

 

 

  1. Fluorescent Light:

 

 

 

 

 

 

  1. Sun:

 

 

 

 

 

Which one(s), if any, of the above showed absorbtion lines,  emission lines?

 

 

What is the wavelength range of each of the colors, in nanometers?      Red:                         Orange:                       Yellow:                         Green:

      Blue:                             Violet:

 

 

  1. Tube A:  (Draw spectrum here)

 

 

 

 

 

                        Identification (from chart on wall):

 

  1. Tube B:

 

 

 

 

 

                  Identification:

 

  1. Tube C:

 

 

 

 

 

 

                        Identification:

 

  1. Tube D:

 

 

 

 

 

                        Identification:

 

  1. Tube E

 

 

 

 

 

                        Identification:

 

           

 

 Questions: 

Define the following terms or phrases:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What are some practical uses for spectroscopy? – list at least four:

1.

 

2.

 

3.

 

4.

 

5.

 

Why does each element produce a unique spectrum?  Talk about electrons in the atom.

 

 

 

 

 

 

What is red shift?

 

 

 

What is blue shift?

 

 

 

 

List and describe at least 6 of the non-visible portions of the electromagnetic spectrum.  Tell why each of the parts of the non-visible spectrum is important to human life and/or understanding?

 

            1.

 

 

 

            2.

 

 

 

            3.

 

 

 

            4.

 

 

 

            5.

 

 

 

            6.

 

 

 

Bonus Question (extra credit):  How can we tell that galaxies are spinning?