Summary

In this lab, students will observe the colors produced when different metal salt solutions are heated in a flame. Students will take on the role of a forensic investigator and use their results to help them determine if collected evidence was contaminated.

Grade Level

High School

Objectives

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

• Use flame tests to identify a metal or metallic salt by the color that it produces when it is put into a flame.
• Identify an unknown metal by the color it emits when passed through a flame.

Chemistry Topics

This lab supports students’ understanding of

• Energy
• Electromagnetic Spectrum
• Atomic structure
• Atomic spectra
• Electrons
• Visible light spectrum
• Identifying an Unknown

Time

Teacher Preparation: 30 minutes (longer if solution preparation is necessary)

Lesson: 45 minutes

Materials

• Metallic Salt Solutions:
  • 50 mL of 1.0M Barium Chloride (BaCl₂) – Note: Barium chloride is highly toxic. Do not ingest the salt or solution.
  • 50 mL of 1.0M Calcium Chloride (CaCl₂)
  • 50 mL of 1.0M Copper Chloride (CuCl₂)
  • 50 mL of 1.0M Lithium Chloride (LiCl)
  • 50 mL of 1.0M Potassium Chloride (KCl)
  • 50 mL of 1.0M Sodium Chloride (NaCl)
  • 50 mL of 1.0M Strontium Chloride (SrCl₂)
  • Evidence Sample from Well (see Teacher Notes)
  • Evidence Sample from Garage (see Teacher Notes)
• Deionized water
• 9, 100 mL beakers for Salt Solutions
• 9, 250mL beakers of water (for extinguishing flame)
• 9 Bunsen burners
• Wooden splints
• Striker

Safety

• Barium chloride is highly toxic. Do not ingest the salt or solution.
• Wear proper personal protective equipment when preparing and working with solutions.
• Wash hands after handling materials used to prepare for or perform this experiment.
• Students should always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Always use caution around open flames. Keep flames away from flammable substances.
• Always be aware of an open flame. Open flames can cause burns. Do not reach over it, tie back hair, and secure loose clothing.

Teacher Notes

• This lab is designed to be set-up as lab stations. Each station should include one 100ml beaker of the metal salt solutions with a number of soaking wooden splints, a Bunsen burner, and a 250ml of water for extinguishing the wooden splint.
• Students should spend 4-5 minutes at each station as the complete the procedure and collect data.
• There are many ways that a teacher can plan for conducting the forensic scenario in this lab. I include two additional stations, one labeled “well” and another “garage,” which are used to decide the outcome of the case. Using distilled water for the “well” sample and a sodium solution for the “garage” would suggest that the misguided youth had nothing to do with the well because they do not match in color. But sometimes I use a sodium salt solution for both the “well” sample and the “garage” sample, suggesting that the students are the sort who like to get into mischief, and did contaminate the well. The situation could be switched up from the morning to afternoon, so that students from different classes can’t share results. Likewise, alternative contaminates could be used in different classes.

Solution Preparation:

• If you need to make ≈1.0M solutions of the metallic salts follow these instructions:
• Label each of the 100 mL beakers with the name of the salt that it will hold.
• Add the solid metallic salts to the beakers:
  • 12.2 grams of Barium Chloride (BaCl₂*2H₂O) – Note: Barium chloride is highly toxic. Do not ingest the salt or solution.
  • 5.5 grams of Calcium Chloride (CaCl₂)
  • 8.5 grams of Copper Chloride (CuCl₂*2H₂O)
  • 2.1 grams of Lithium Chloride (LiCl)
  • 3.7 grams of Potassium Chloride (KCl)
  • 2.9 grams of Sodium Chloride (NaCl)
  • 7.9 grams of Strontium Chloride (SrCl₂)
• Add deionized water up to the 50 mL mark.
• Note: if you do not have 100 mL beakers, substitute another piece of glassware and use a 50 mL graduated cylinder to add the deionized water.
• Use a separate wooden splint to stir each of the solutions.
• Distribute the remaining wooden splints between the solutions.
• Allow the splints to sit in the solutions overnight.
• One at a time, slowly pass the wooden splints through the burner flame. Repeat with additional splints until students have identified color. The flame will color as follows:
  • Barium Chloride: light green
  • Calcium Chloride: orange red
  • Copper Chloride: blue/green
  • Lithium Chloride: pink/fuchsia
  • Potassium Chloride: light lilac
  • Sodium Chloride: yellow flame
  • Strontium Chloride: red or crimson flame