Ethanol solutions of metal salts are sprayed into a burner flame producing brilliant fireballs with the characteristic color of each metal.
This demo is usually used when discussing atomic structure to illustrate that electron transitions are discrete and characteristic of a particular element. Allow about 5 minutes for this demo.
As the metal ions are heated by the burner flame, some of their electrons absorb energy and move to excited states. As the electrons return to a lower energy, they emit light of a characteristic frequency corresponding to the amount of energy that they lost moving to the lower energy level. Since the frequency and color of the light are characteristic of a particular metal, flame tests are sometimes used as an analytical test for the presence of certain metal ions.
- four Nalgene aerosol spray bottles containing solutions of copper acetate, potassium acetate, strontium nitrate, and sodium acetate in ethanol
- propane torch
- Light the burner.
- Dim the lights.
- Spray each solution into the flame of the burner. If necessary, pump the bottle cap a few times to pressurize the bottle. Do not get the spray bottles too close to the flame. Be sure that the spray is directed away from any observers.
- The metal salts in solution are copper acetate (green), potassium acetate (violet), strontium nitrate (red), and sodium acetate (yellow).
- Turn off the burner.
- Do not get the spray bottles too close to the flame.
- Be sure that the spray is directed away from any observers.
- Remove all flammable materials from the area of the demonstration.
- Ethanol is very flammable. Be sure that there is a fire extinguisher nearby.
- Wear goggles.
If the bottles have been stored for a while, test them. If the ones that aren't supposed to contain sodium ion are contaminated with the yellow-orange color of sodium the entire apparatus needs to be broken down and cleaned with an analytical-grade laboratory detergent and rinsed with deionized water. Then the spray bottles should be restocked with fresh solutions.
The concentration of the solutions is not critical as long as there is enough ion present to produce a brilliant flame color.