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

  1. 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.
  2. Soak separate wooden splints in each solution overnight; reserve a water beaker to quench used splints.
  3. Set up a Bunsen burner in a clear area and light it with a striker; dim room lights if possible.
  4. 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.
  5. Record the observed color and estimate wavelength or frequency using a visible spectrum chart.
  6. For a mixture test, place a copper and a strontium splint in the flame together and identify both colors present.
  7. If desired, present two unknown splints for students to identify from their color matches.

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?