Colored Fire Spray Bottles

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Colored Fire Spray Bottles
Colored fire spray bottles work on the same principle as the flame test in chemistry.

Colored fire spray bottles are a classic chemistry demonstration that delights the audience and raises interest in chemistry. In the pilot episode of “Breaking Bad”, chemistry teacher Walt White performs a demonstration in which he changes the color of a Bunsen burner flame by spraying the flame with chemicals. You can perform the colored fire demonstration yourself. All you need are some common chemicals, alcohol, and spray bottles. Here is a list of metal salts you can use to (safely) color fire. Also, there is a safer procedure that uses water instead of alcohol and reduces the risk of accidents.

Colored Fire Spray Bottle Chemicals

The classic demonstration uses metal salts dissolved in methanol or another alcohol. Spritzing a blue or nearly colorless Bunsen burner flame reveals the colors.

Here’s a list of common chemicals and the colors of flames they produce:

  • dark red = lithium chloride
  • red = strontium chloride (found in emergency flares and red sparklers)
  • pink = lithium chloride + potassium nitrate
  • orange = calcium chloride (a bleaching powder)
  • yellow = sodium chloride (table salt) or sodium carbonate (washing soda)
  • yellowish green = borax (sodium borate, a common insecticide and cleaning agent)
  • green = copper sulfate (pool and aquarium algicide, root killer)
  • blue = copper(I) chloride (lab chemical)
  • violet = 3 parts potassium sulfate, 1 part potassium nitrate (saltpeter)
  • purple = potassium chloride (salt substitute)

Many of these chemicals occur in the home. Others are available online. Other metal salts produce colors, but the ones on this list are preferable because they have low toxicity.

Prepare the Flame Colorants

If you were just coloring a campfire or other wood fire, you could simply sprinkle the dry metal salts onto the fire. Copper chloride is especially nice for this since the sodium that is naturally present in wood causes this chemical to produce a mix of blue, green, and yellow flames. However, for the gas flame in a burner, you need the salts dissolved in a flammable liquid. The obvious choice here is alcohol. Common alcohols found around the home include rubbing alcohol (isopropyl alcohol) and ethanol (e.g., in vodka). Another option is methanol (a fuel treatment), but it is highly toxic.

  1. Add 100 milliliters of alcohol to each spray bottle.
  2. Label the bottles before adding the metal salts.
  3. Add 5 grams of chemical per bottle.

So, if your bottle is smaller, use less alcohol and less salt. For example, dissolve 5 grams of metal salt in 50 milliliters of alcohol. The amount is not critical, so accurate measurements are unnecessary.

Perform the Colored Fire Spray Bottles Demonstration

  1. In separate small spray bottles, dissolve a chemical in a small amount of alcohol.
  2. Stand away from the burner flame and spritz the liquid in the bottle toward the flame. Remember, alcohol is flammable, so the size of the flame expands when you spray it.
  3. Repeat with other chemicals.

Safety Information

While the colorants used in this demonstration are generally safe, this project involves flammable materials and flames.

  • Always have a fire extinguisher when working with flames.
  • Keep the demonstration free of flammable materials.
  • Secure long hair and loose clothing.
  • Remember gas flames, as from burners, are often nearly invisible.
  • Never spray chemicals toward a person, pet, or object.
  • Wear eye protection and long clothing.
  • Ideally, separate the demonstration from the audience using a clear barrier. Otherwise, have viewers stay 10 feet (3 meters) away from the flame.

How Colored Fire Spray Bottles Work

Heat from the burner flame imparts energy to the chemicals. Atoms absorb the energy, raising electrons to a higher energy state. The excited electrons return to a lower energy state, releasing photons (light) in the process. The wavelength of color of the light is characteristic of the atomic emission spectrum of the chemical.

A Safer Version of the Demonstration

You do not need to spray a flame with flammable chemicals to see colored fire. While less dramatic, a safer version uses metal chlorides dissolved in water and wooden splints. Chlorides work for this variation because they are soluble in water. Chlorides also enhance color, so they are popular in firework formulations. But, if you can’t find chlorides, substitutes include nitrates and acetates.

  • Strontium chloride (SrCl2) – red
  • Sodium chloride (NaCl) – yellow
  • Potassium chloride (KCl) – pale violet
  • Lithium chloride (LiCl) – red to pink
  • Copper chloride (CuCl or CuCl2) – blue-green to green
  • Calcium chloride (CaCl2) – orange
  1. In 6 separate small jars, dissolve the metal salts in a small amount of water.
  2. Soak the ends of wood splints in the solutions.
  3. When you are ready for the demonstration, use a striker and light the burner.
  4. Insert the end of a soaked splint in the flame and observe the color. Note that the damp sticks do not ignite. Move the splint around in the flame and ensure it does not burn.
  5. Place the used splint in a bowl of water.
  6. At the end of the project, if you have unused soaked splints, let them dry for later use.

References

  • Landis, Arthur M.; Davies, Malonne I.; Landis, Linda; Thomas, Nicholas C. (2009). “‘Magic Eraser’ Flame Tests”. Journal of Chemical Education. 86 (5): 577. doi:10.1021/ed086p577
  • Reynolds, R. J.; Thompson, K. C. (1978). Atomic Absorption, Fluorescence, and Flame Emission Spectroscopy: A Practical Approach. New York: Wiley. ISBN 0-470-26478-0.
  • Sanger, Michael J.; Phelps, Amy J.; Banks, Catherine (2004). “Simple Flame Test Techniques Using Cotton Swabs”. Journal of Chemical Education. 81 (7): 969. doi:10.1021/ed081p969
  • Uden, Peter C. (1992). Element-specific chromatographic detection by atomic emission spectroscopy. Columbus, OH: American Chemical Society. ISBN 0-8412-2174-X.