Rainbow Fire

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Abstract

Objective

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

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).

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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 and Concepts

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?
• What is flame spectrometry and how is it used by physicists and chemists?
• How does this science project relate to what astronomers do when they are trying to identify the atomic makeup of a star?
• What are metal ions? In the chemicals used in this science project which elements in the compounds are metals?

Bibliography

Here are some good references to get you started with your background research:

• Goldman, M.V., et al. (2000). Spectral Lines. Retrieved October 16, 2012 from http://www.colorado.edu/physics/2000/quantumzone/index.html
• Wikipedia contributors. (2012, October 15). "Spectral Lines." Wikipedia, The Free Encyclopedia. Retrieved October 16, 2012 from http://en.wikipedia.org/w/index.php?title=Spectral_line&oldid=517881133
• Niece, Brian K. (2006). Atomic Spectra. Retrieved October 16, 2012 from http://www1.assumption.edu/users/bniece/spectra/tutorials/AS_Introduction.html

Materials and Equipment

Supplies for this project are available in one convenient kit from the Science Buddies Store

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

• White glue (1 small bottle), such as Elmer's
• Bamboo skewers (12)
  • Science Buddies Kit: The kit contains 24 skewers, enough to do the experiment twice.
• Chemicals; 12 grams (g) each of:
  • Copper sulfate
  • Strontium chloride
  • Boric acid
  • Sodium chloride
• Masking tape
• Pen or marker
• Small vials or ziplock bags for the chemicals (4)
  • Science Buddies Kit: Each chemical in the kit has its own jar just large enough for the chemical plus a skewer tip. No additional vials or ziplock bags are needed.
  • Vials should be fairly narrow and short; just large enough to hold the chemicals and 1 inch of the tip of a bamboo skewer.
  • Ziplock bags should be small; 2" x 2" or 2" x 3" would be ideal.
• Chemical goggles
• Disposable latex or nitrile gloves
• Paper towel (4 sheets)
• Matches (1 box); the strike on box kind work best but any type will do
• Solid fuel tablet (1); Esbit 14 g tablets available from Amazon.com work well
  • Science Buddies Kit: The kit contains 2 tablets, enough to do the experiment twice.
• Aluminum foil
• Hard nonflammable outdoor surface like a sidewalk, driveway, or brick/concrete patio
• Container of water
• Heat resistant bowl (1); a soup or cereal bowl would work well
• Lab notebook
• Optional: video camera or digital camera and tripod
• Optional: flashlight

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Experimental Procedure

Preparing the Chemical Skewers

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 (a day or more is also fine), prepare the bamboo skewers. . You will be making 3 skewers per chemical.
4. Put a piece of masking tape around the blunt end of each skewer (a total of 12 skewers) like a flag as seen in Figure 1 below. With a pen, write the name of a chemical on each skewer's masking tape label.
   1. In the end you should have 3 skewers labeled for each chemical.

Figure 1. A completed skewer is shown here. Notice the masking tape label at the blunt end, and the copper sulfate coating approximately 1 inch of the tip.

5. Apply a thin layer of glue to the last 1 inch of the tip of a skewer as shown in Figure 2.
   1. Just a little bit of glue is enough.
   2. You can squeeze the glue directly from the glue bottle onto the skewer.

Figure 2. Cover approximately 1 inch of the tip of each skewer with a small amount of glue. Make sure the glue is on all sides of the skewer.

6. While wearing the chemical goggles and disposable gloves, dip the glue-coated tip end of the skewer in the jar of chemical. Twist the skewer back and forth a bit to coat the skewer with the chemical.
   1. Make sure the name of the chemical on the skewer label is a match for the chemical you are using.
   2. If you are not using the Science Buddies kit you may need to put your chemicals into vials or small ziplock bags to do this step. The Science Buddies Kit chemical jars are just the right size to coat the skewer in.
7. Repeat steps 5 and 6 until you have made 3 skewers for each of the chemicals.
8. Let the skewers dry for at least two hours before performing the flame tests.

Conducting the Flame Tests

1. The flame test should be conducted outside, in the dark (or at twilight), on a hard nonflammable surface. Adult supervision is needed.
2. Find a hard nonflammable surface outside for the flame test. A driveway, sidewalk, or brick/concrete/cement patio are all examples of a good testing surface.
3. Bring the dried chemical skewers (make sure they have dried for at least two hours first) and all other materials outside. You may find it easiest to use a flashlight or other outdoor light while you are getting set up. When you are done setting up and ready to test the skewers make sure to turn off the light(s).
4. Place a solid fuel tablet on a square of aluminum foil on your nonflammable surface as shown in Figure 3.

Figure 3. Outside on a nonflammable surface is the ideal place to conduct your flame test. For easy cleanup make sure to but your solid fuel tablet on a square of aluminum foil.

5. As a safety precaution make sure to have a container of water with you. A fire extinguisher would be a fine alternative. If you are using a video camera, start recording.
6. Have an adult use a match to light the solid fuel tablet. You may find that laying the lighted match on the foil next to the tablet is the easiest way to get the tablet to start burning. Note the color of the flame in your lab notebook. If you are using a digital camera to document your experiment, take a picture of the burning tablet.
7. Once the solid fuel tablet is burning, carefully take a skewer and hold the chemical coated end in the flame. Observe the flame color and record it in your lab notebook. Take a photo if you are using a digital camera for documentation.
   1. The skewer may also catch fire after a few moments. Simply remove it from the flame and blow it out like a birthday candle. You can also extinguish the skewer in the container of water.
8. Repeat step 7 for all 12 skewers (3 per chemical). Record all your observations in your lab notebook.
9. When you are done either wait for the solid fuel tablet to burn itself out or extinguish it by carefully putting a heat resistant bowl over the tablet, as shown in Figure 4, for a few minutes.

Figure 4. The solid fuel table will burn itself out in under 20 minutes. If you do not want to wait, you can extinguish it by covering it with a heat resistant bowl for 1 minute. This will deprive the fire of oxygen thus causing the flame to go out.

10. When you are sure everything has been extinguished, you can dispose of the aluminum foil, used chemical coated skewers, and spent fuel tablet in the garbage.
11. What colors were produced as each chemical burned?
12. Sodium chloride (table salt) and strontium chloride both have a chloride ion, but have a different metal ion (sodium vs. strontium). Are the flame colors produced by these two compounds similar or different? What does this tell you about the source of the color?

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