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JoVE Lab Manual
Lab: Chemistry

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Education
Metal Flame Emission
 

Learning Objectives

At the end of this lab, students should know...

How do electrons move to a higher energy state?

When an electron absorbs energy equal to the energy difference between the ground state and a higher energy excited state, it moves to that higher energy state. Electrons must transition to specific energy levels, which means they can only absorb specific quantities of energy.

What happens when an electron relaxes back down to a lower energy state?

When the electron relaxes back to a lower energy state, it releases energy in the form of a photon.

How is the metal flame emission test performed?

The metal flame emission test is performed by placing a metal sample in a flame and observing the flame color, which corresponds to a specific metal. Each element has a unique emission due to its electronic configuration.

Why measure an emission spectrum when performing the flame test?

Most metal samples contain metal ions, oxides, and salts, which all absorb and emit different wavelengths of light. The emission spectrum is used to determine the relative amount of each substance in the sample and can be used to identify components of a sample.

What is the difference between absorbed and emitted light?

The emitted light is the energy that is released during electron relaxation. Emitted light and absorbed light are complementary to each other in the color wheel. Emitted light is produced as a photon of a particular energy when excited electrons transition to lower energy levels and produce different wavelengths of light.

List of Materials

  • Data acquisition device
    2
  • UV-Vis spectrophotometer
    2
  • Fiber-optic cable with CCD
    2
  • Test tube rack
    2
  • 10 x 75 mm test tubes
    12
  • Disposable spatula
    6
  • 400-mL glass beaker (+1 for instructor's hood)
    2
  • 6" cotton-tipped applicator with wood handle
    12
  • Flash drive
    2
  • Sparkler
    2
  • Bunsen burner with tubing (+1 for instructor's hood)
    2
  • Fire striker (+1 for instructor's hood)
    2
  • 250-mL glass Erlenmeyer flask
    1
  • 250-mL plastic wash bottle
    1
  • NaCl
    50 g
  • BaCl2·2H2O
    50 g
  • KCl
    50 g
  • LiCl
    50 g
  • CuCl2·2H2O
    50 g
  • SrCl2·6H2O
    50 g

Lab Prep

Source: Smaa Koraym at Johns Hopkins University, MD, USA

  1. Lab Preparation for Metal Flame Emission Testing

    Here, we show the laboratory preparation for 10 students working in groups of 5, with some excess. Please adjust quantities as needed.

    • Put on a lab coat, safety glasses, and nitrile gloves.
    • Barium, copper, and strontium require special disposal, so place an appropriate waste container and a wash bottle of deionized water in the waste hood.
    • Prepare a spectrophotometer for each student group. Confirm that the devices are working and charged before distributing them to the student's fume hoods.
    • Set a Bunsen burner, a length of latex tubing, a striker, a sparkler in a 250-mL Erlenmeyer flask, and a 400-mL glass beaker in the main instructor's hood.
    • Prepare the metal salts. For each student group, place 6 small test tubes in a rack.
    • Label the 6 tubes as 'Na', 'K', 'Li', 'Ba', 'Sr', and 'Cu'. Prepare an extra rack as a backup.
    • Obtain the metal salts and a few paper towels to catch any spills. Use a small disposable spatula to fill each Na tube with NaCl to a depth of about 2 mm. Discard the spatula afterward.
    • Fill the remaining tubes in the same way using a clean spatula for each metal to prevent cross-contamination.
    • Place a rack of filled test tubes at each fume hood. Store the extra rack in the instructor's hood and clean up any traces of spilled salts.
    • Distribute a Bunsen burner and striker to each fume hood.
    • Lastly, just before the lab, fill a 400-mL beaker with deionized water for each student group and place 6 cotton-tipped applicators tip down in each beaker. Set one at each fume hood.

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