demonstrations:flame_tests
Flame Tests
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★☆ Some safety precautions required to perform safely
Categories: Atoms, Elements and Periodic Table
Alternative titles: Flame Test Colors
Summary
Different metal ions produce characteristic flame colors when their solutions are heated in a flame.
Procedure
- Label small beakers for each metal salt and prepare about 50 mL of ≈1.0 M aqueous solutions for BaCl2, CaCl2, CuCl2, LiCl, KCl, NaCl, and SrCl2.
- Soak separate wooden splints in each solution overnight; reserve a water beaker to quench used splints.
- Set up a Bunsen burner in a clear area and light it with a striker; dim room lights if possible.
- One at a time, pass a soaked splint slowly through the hottest part of the flame and observe the color; place the used splint in the water beaker.
- Record the observed color and estimate wavelength or frequency using a visible spectrum chart.
- For a mixture test, place a copper and a strontium splint in the flame together and identify both colors present.
- If desired, present two unknown splints for students to identify from their color matches.
Links
Flame Test Colors - Step by Step Science:
The Flame Test Experiment- The Chemistry of Colorful Flames - Chem Camp with Mrs. Newman:
📄 The Flame Test - ACS Institute: https://institute.acs.org/acs-center/lab-safety/education-training/safer-experiments/flame-test.html
Variations
- Look at through a spectroscope to filter the individual color bands.
- Spray the solutions onto a flame using a perfume sprayer.
Safety Precautions
- Wear safety goggles, lab coat or apron, and tie back hair.
- Use only aqueous salt solutions on splints; do not use flammable solvents such as methanol or ethanol.
- Keep flammables away from the burner and maintain a clear workspace.
- Some salts are highly toxic; refer to safety data sheets before use.
- Quench used splints in water and dispose of residues sensibly.
Questions to Consider
- Which ions produced each flame color, and how can color be used to identify an unknown?
- Using c = λν, convert an observed wavelength to frequency and vice versa; which colors correspond to higher energy photons?
- How do electronic energy levels and electron transitions explain the observed discrete colors?
- How is this safer method different from the traditional rainbow demo that used alcohol fuels on the bench?