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Spectral Detective (10 Favorites)

LAB in Interdisciplinary, Atomic Spectra, Identifying an Unknown, Emission Spectrum, Electromagnetic Spectrum, Emission Spectrum. Last updated January 25, 2019.


Summary

In this lab, students will use a spectroscope to view the atomic spectra of various unknown elements. Using their collected data in combination with known atomic spectra, they will identify the chemical elements.

Grade Level

Middle School or High School

Objectives

By the end of this lesson, students should be able to

  • understand how a spectroscope works.
  • use a spectroscope to match an unknown spectrum to its chemical element.
  • understand how diffraction can separate light into its component colors.

Chemistry Topics

This lesson supports students’ understanding of

  • Atomic structure
  • Atomic spectra

Time

Teacher Preparation: 30 minutes

Lesson: 60 minutes

Materials

  • Spectroscope (one per pair of students)
  • Known Chemical Element Spectra sheet (one per pair of students)
  • Chemical element gas discharge tubes (at least 6 - Hydrogen, Helium, Nitrogen, Oxygen, Neon, Sulfur, Argon, Krypton, Iodine, Mercury)
  • Power supply for the gas discharge tubes
  • Colored pencils

Safety

  • Students should not touch or attempt to remove the gas discharge tubes from the power supply.
  • Never look directly into the sun with the spectroscope.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials.

Teacher Notes

  • It is best if the students work with a partner when using the spectroscope.
  • A clearer spectrum is formed if the discharge tubes are surrounded by a box or other materials to block out ambient light sources.
  • Inexpensive spectroscopes, as well as the gas discharge tubes and power supply, can be purchased from a source such as www.amazon.com.
  • As an extension, the students could use the spectroscope to see how the spectrum shifts when the bulb is moved closer or further away from the spectroscope (Doppler Shift).
  • Use a classroom projector to show the prelab video: NASA Launchpad: Neon Lights – Spectroscopy in Action

For the Student

Lesson

Prelab Questions

  1. When scientists look at stars that are hundreds (or more) light years away, they can determine the chemical elements that make up that star. How do you think that a scientist can do this even though the star is too far away for a spaceship to reach?
  2. We are now going to watch a short video: NASA Launchpad: Neon Lights – Spectroscopy in Action
    At the conclusion of the video, re-answer the above question.

Problem

How can you identify unknown chemical elements?

Materials

  • Spectroscope (one per pair of students)
  • Known Chemical Element Spectra sheet (one per pair of students)
  • Chemical element gas discharge tubes
  • Power supply for the gas discharge tubes
  • Colored pencils

Procedure

  1. Record the letter on the first discharge tube in the data table below.
  2. Point the spectroscope’s slit at the first gas discharge tube, so the light is entering the spectroscope. Make sure that the slit is in a horizontal position.
  3. While the light is entering through the slit, look through the circular opening at the other end of the spectroscope and adjust the spectroscope until you see a spectrum (rainbow of many lines of color). The spectrum will appear off to the side.
  4. Sketch the exact spectrum that you see using colored pencils in the data table below.
  5. Compare your sketch to the pictures to the spectra on the Known Chemical Element Spectra sheet. Look for a match.
  6. Determine the type of chemical element and record its name on the data table below.
  7. Repeat steps 1-6 for all of the other gas discharge tubes.

Data

Discharge Tube Letter Spectrum Sketch
Type of Chemical Element

Analysis

  1. How can you use a spectroscope to identify chemical elements? Write your response in CER (claim, evidence, reasoning) form.
  2. Take your spectroscope outside and look at the sky (DO NOT LOOK DIRECTLY AT THE SUN). You should see a rainbow pattern in your spectroscope. What chemical elements do think are in the sun? Explain why you think that these elements are in the sun.
  3. Some types of light bulbs look like they are a certain color, such as yellow or bluish. Using what you have observed with the spectroscope today, why might this be?