Flame Photometry - Discovering the Emission Spectrum - Eva Varga

In this activity, 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?

Materials

• Boric acid
• Copper sulfate
• Strontium chloride
• Sodium chloride (table salt)
• 2 glasses of water
• wooden skewers
• Clean Burning Fuel Tablets

Experiment

1. Dip the skewer in water.
2. Dip the wet skewer into the boric acid.
3. Dim the lights and place the boric acid-covered skewer into a flame. What color does the flame produce?
4. Extinguish flame by placing skewer into another glass of water.
5. Dip another skewer in water.
6. Dip the wet skewer into the sodium chloride (table salt).
7. Again, dim the lights and place the sodium chloride-covered skewer into a flame. What color does the tartar flame produce?
8. Extinguish flame by placing skewer into another glass of water.
9. Repeat with the remaining chemicals, testing them one at time.

When you are sure everything has been extinguished, you can dispose of the used chemical coated skewers and spent fuel tablet in the garbage. What colors were produced as each chemical burned? 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?

Explanation

The experiment that you just conducted is called a flame test.  Flame photometry is a procedure used  to detect certain elements in a material. When you put the boric acid in the flame, you should have notice a bright green flame. The green flame denotes the presence of the element Boron. The cream of tartar should have yielded a purple flame, the color associated with the presence of potassium (cream of tartar is a potassium salt). These element-specific colors are a result of their emission spectrum. The emission spectrum of an element is the color emitted when an atom’s electrons make a transition from a high energy state to a low energy state.

Questions to Ponder

• 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 activity 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?