Abstract

Objective

The goal of this project is to investigate the colors produced when different chemicals are burned.

Introduction

All matter is made of atoms. Atoms have a nucleus, consisting of protons and neutrons, surrounded by electrons. The nucleus is concentrated in a very small space, about 10⁻¹⁵ m. An entire atom is on the order of 10⁻¹⁰ m, so the electrons are relatively far from the nucleus, and, strangely enough, atoms are mostly empty space.

Physicists have found that the electrons traveling around the atomic nucleus can have only certain specified energy levels. In other words, the energy levels of atomic electrons are quantized. When provided with more energy, the electrons can move from one energy level to another, but these different energy levels are not continuous—they come in discrete steps. This fundamental discovery is known as quantum mechanics. Quantum mechanics describes how an atom's electrons interact with electrons of other atoms and with photons.

Atomic electrons at higher energy levels can also lose energy, dropping down to a lower energy level. Again, the electron moves from one allowed energy state to another. The lost energy can be carried away in the form of heat (vibrational energy) or in the form of light—when the electron reverts to a lower energy state, a photon of light is produced. The photon produced will have an energy equal to the difference between the electron's initial high energy state and the later lower-energy state. For visible light, we perceive these differences in photon energy as differences in the color of the light.

In this project, you will use a procedure that is similar to flame photometry to observe the color of light produced when various chemical compounds are burned. You'll need an adult to help you with this experiment, and you will have to perform the experiment extremely carefully so that the flames stay small and under control. What colors will different chemicals produce?

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Atoms
• Protons
• Neutrons
• Electrons
• Photons
• Flame photometry
• Ions
• Metals
• Non-metals
• Spectral lines
• Atomic spectroscopy

Questions

• How are the colors produced by a chemical when it burns related to the atomic structure of the chemical?

Bibliography

• Here are some good references on spectral lines to get you started with your background research:
  • Goldman, M.V., et al., 2000. "Spectral Lines," Physics 2000 [accessed August 17, 2007] http://www.colorado.edu/physics/2000/quantumzone/index.html.
  • Wikipedia contributors, 2007. "Spectral Lines," Wikipedia, The Free Encyclopedia [accessed August 17, 2007] http://en.wikipedia.org/w/index.php?title=Spectral_line&oldid=150188421.
• You can read about flame photometry on this webpage:
  Resonance Publications, date unknown. "Atomic Spectroscopy," Resonance Publications [accessed August 17, 2007] http://www.resonancepub.com/.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• Chemical safety goggles
• Fire extinguisher
• Pinecones (15). If you can't find pinecones, substitute something else that will burn easily, like sheets of balsa wood from a craft store.
• White glue (1 bottle), such as Elmer's
• Fireplace, campfire ring, outdoor barbeque pit, or other place where you can safely burn a pinecone.
• Tablespoon measuring spoon (1)
• Flashlight
• Ziplock bags, gallon size (4)
• Masking tape (1 roll)
• Pen or marker (1)
• Chemicals for testing flame color:
  
  • Sodium chloride (table salt), available at grocery stores
  • Boric acid (powdered roach killer), available at drug stores or hardware stores
  • Lithium chloride, available online at http://www.sciencecompany.com/sci-exper/flamecolors.htm, catalog #NC-4851
  • Copper sulfate, available online at http://www.sciencecompany.com/sci-exper/flamecolors.htm, catalog #NC-0304
• Matches
• Camera and tripod
• Lab notebook

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Experimental Procedure

1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
2. Have an adult present when you do the experiment, and follow all of the safety precautions, above.
3. Several hours before sunset, prepare the pine cones. Using the paintbrush, apply a thin layer of glue to three of the pinecones. These are the controls and will have no chemical applied to them.
   1. Attach a piece of masking tape with the word "control" to each pinecone.
   2. Set the pinecones aside to dry.
4. Take the first chemical, sodium chloride, and measure four tablespoons into a ziplock bag.
5. Using the paintbrush, quickly apply a thin layer of glue to a pinecone and then put it in the ziplock bag with the sodium chloride. Shake the bag to coat the pinecone thoroughly in sodium chloride.
   1. Work quickly to coat the pinecone before the glue dries.
   2. Attach a piece of masking tape with the words "sodium chloride" to the pinecone.
   3. Set the pinecone aside to dry.
   4. Repeat steps 4-5 for two more pine cones until you have a total of three pinecones coated with sodium chloride.
6. Repeat steps 4-5 for the remaining pine cones and chemicals. Make sure to carefully wipe off and wash the measuring spoon when you switch chemicals. In the end you should have pine cones coated with:
   1. No chemical, just glue (3). These are your controls.
   2. Sodium chloride (3).
   3. Boric acid (3).
   4. Lithium chloride (3)
   5. Copper sulfate (3)
7. Once the pinecones are dry and it has gotten dark outside, set up your camera on its tripod directly across from the fireplace, or other burning area, you'll be using. Adjust the camera's settings to take photos without flash.
8. Place 1 control pinecone in the fireplace.
9. Carefully use the match to light the pine cone. Either have an adult do this step, or make sure an adult is present to ensure your safety.
10. Observe the color of the flame, and photograph it with your camera. Record all observations in your lab notebook.
    1. You'll be able to observe the colors best (and get the best pictures) if the background is dark, so try doing this experiment at twilight, or in some other dim outdoor setting.
    2. By studying the photographs of the different chemical flames side-by-side at the end of the experiment, you may notice subtle differences that you did not originally pick up on. Make sure to keep all your camera settings constant during the experiment in order to make the most accurate comparisons.
11. Repeat steps 8-10 two more times to confirm that the flame color is reproducible.
12. Repeat steps 8-11 using the chemical coated pine cones. Burn each pinecone by itself.
13. What colors were produced as each chemical solution burned?
14. Sodium chloride (table salt) and lithium chloride both have a chloride ion, but have a different metal ion (sodium vs. lithium). Are the flame colors produced by these two compounds similar or different? What does this tell you about the source of the color?

Variations

• For more science project ideas in this area of science, see Physics Project Ideas.

Credits

Andrew Olson, Ph.D., Science Buddies

Justin Spahn, Science Buddies

Sandra Slutz, Ph.D., Science Buddies

Sources

This project is based on an entry to the 2007 San Mateo County (California) science fair (author names not published).

Last edit date: 2010-10-06 13:45:00