Introduction:
Define EMR, wavelength, frequency, and energy of EMR. Give the equations that relate each. Explain what is meant by the emission spectra of atoms. Give the Rydberg-Balmer equation and for what it is used. Explain what happens when electrons are excited by an electrical current or heat from a Bunsen burner and why it often produces visible light. This link should prove to be very helpful.
Procedure:
Line Spectra
Read the brochure accompanying each spectroscope, then look through your spectroscope at the overhead light and or the light from the window. Note the colors and the range of numbers on the scale above the spectrum. Describe.Using your spectroscope look at each of the 2 spectrum tubes, Helium and Hydrogen and record the wavelength and color of each line you see and use colored pencils to make a sketch of how the lines look to you.
Flame Tests
The Visible Spectrum
- Knowns: Test each solution by soaking a cotton swab in distilled water, then squeezing out the excess water. To obtain the flame spectrum for a given solution, dip the swab into the solid compound, and then place the tip of the swab in the hottest part of the Bunsen burner flame (the part immediately above the cone of the flame). Record the color (or colors) observed in your data table. Repeat the procedure for all the salt solutions provided using a fresh swab for each.
- Unknown(s): Test the three unknowns as described above using a new swab for each unknown. Record the identity label of your unknown(s) along with your observations. Identify your unknow(s)in your Results.
Take a piece of chalk cut at a slant and place it in a test tube the same size as the cuvettes and put it into the sample holder os a Spec 20 with the slanted side facing the light source of the Spec 20. Observe and record the color of the beam every 50 nm from 650 nm until 350 nm. You may adjust the brightness knob for those wavelengths where the light appears dim or too bright. Use colored pencils to draw a color spectrum in your lab book, labeling the wavelength where the color changes. Next, set the wavelength to 600 nm. Note the color(s) you see. How many different wavelengths of light make up the band of light you see? Now adjust the wavelength to 550 nm. Rotate the brightness knob and see how the light intensity changes with the rotation. Be sure you note the variation in light intensity across the band that you see.
Data Analysis
Use a spreadsheet to calculate the frequency and energy for each line for each element.For hydrogen only, use your spreadsheet with the Balmer-Rydberg equation and your hydrogen wavelengths to calculate the energy level transition for each line. Compare to the Balmer series. Solve the equation for the value of n for each line.
Results and Discussion
Compare your lines for the helium and hydrogen with those on the spectrum chart. These are expected to be the "true" values. Don't worry about the color in the green-yellow region, the color scale is off, but the wavelength values of the lines are okay.Identify the three unknowns you tested in the flame tests.
What is the range (in nanometers) for each of the colors in ROYGBIV? Compare the limits on each side of the visible spectrum that you can see with two people other than your partner, in your class. How do the colors you see for the different wavelength compare to the colors seen by these two other students? What specific color do you see at 510 nm?
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