Atomic Theory

Atomic Spectra Lab - Flame Tests

Flame testing is a simple experimental procedure based on visible light emission. It is particularly useful in identifying certain metallic elements. With this method, a bunsen burner is used to provide the energy to excite the electrons in the atoms, and then one observes a particular color of light as the electrons return to lower energy levels. This color, as well as the corresponding line spectrum, are characteristic of the metal. In this lab you will look at different metal solutions and see what flame color each produces.
Line spectrum of elements are also useful in identifying the element. In this lab you will look at three different elements and record the line spectrum.

Before you come into lab:
In your lab book, write a title, introduction/background, hypothesis, brief procedure, and two data tables. Your introduction/background should relate how colors are produced from an element in a flame, how line spectrum are made (include diagrams showing when lines are formed) and why different colors are seen in the spectrum. Be thorough in this part, use your notes as well as the text but state this in your own words. State the purpose behind this lab as well. For your hypothesis you just need to state if you think you will see different colors for the metal solutions when burned and why. (Read the procedure so this makes more sense.)

Procedure:
Materials required for each group:
bunsen burner, goggles, diffraction grating, discharge tubes, wood splints which have been soaking in metal solutions of Na⁺, Ca⁺², Ba⁺², Sr⁺², Cu⁺², Li⁺, and K⁺.

Part I.

1. Obtain a wood splint of each solution. Be sure to label the splint on the end that is dry. Be careful not to touch different wood splints together.
2. Light your bunsen burner, obtain a blue cone.
3. Hold a wood splint briefly in the flame and observe the color. Record your observations.
4. Repeat step 3) for each sample except K⁺.
5. Repeat step 3) for K⁺. Get a fresh wood splint and use a piece of blue cobalt glass to look through while observing the flame. Record your observations. When finished, turn off the burner and throw the splints in the trash.

Part II.

1. Look through the spectroscope at the fluorescent light to calibrate the scope.
2. Look at the three discharge tubes. Record element, colors, and wavelength.

Questions: (these belong in the data analysis section)

1. At times, sodium contamination can prevent the potassium color from being seen. Blue cobalt glass is used to see the potassium flame when sodium contamination is present. Why does this help?
   
2. Why do different metals have different characteristic flame test colors?
   
3. Could flame tests be useful in determining identities of metals in a mixture? If so, what problems might arise? If not, why not?
   

Evaluation: As usual.
Conclusion: As usual.

 

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