Chem
Name: ______Date: ______Block: ____
Flame Tests
Background:
When elements are heated to high temperatures, they may be placed in an excited state. In an excited state, the electrons move to higher energy levels. The changes in energy that occur when the excited atoms return to their ground state cause the substance to be luminous or emit light. The observed colors or spectrum of the substance is caused by the set of visible wavelengths of light emitted. Since each element emits a unique set of wavelengths, emission spectra can be used as a tool to identify the elements. (Note: Different wavelengths correspond to different colors – below is the visible spectrum of light. For the entire electromagnetic spectrum of light, both visible and invisible, see p. 120 of your textbook.)
One method used to demonstrate the emission spectrum of a substance is the flame test. Using this method, a small amount of a substance is heated and the characteristic glow of the substance is observed. In this experiment you will perform a flame test on several metallic salts. Based on your observations, you will develop a reference table which lists the flame color for each metal ion. You will then perform a flame test on an unknown substance. By comparing your observations to the data in your reference table, you will be able to identify the metal ion in the unknown substance.
Objectives:
In this experiment, you will
· Observe the spectra emitted from selected ions;
· Identify metallic ions by the color emitted during vaporization of the element;
· Evaluate the usefulness of this method of metal identification.
Equipment:
Chem
Bunsen burner
flint lighter
test tube rack
test tubes containing metallic ion solutions
wooden splints
Chem
Lab Writing Assignment:
With your group members, you will complete a formal lab report that will count as a TEST GRADE.
Report Requirements:
1. Use a professional font, size 12 (examples = Times New Roman, Courier New, Arial, Tahoma, etc.)
2. Every section of the report must have a heading in BOLD.
3. Report should be single-spaced, but you may skip spaces between sections or between questions in the Analysis/ Conclusions section.
4. Margins of the document should be 1” all around. You can change margins in the Page Setup section under the File menu.
Procedure:
1. Dip a clean wooden splint in a solution of your first metallic salt and heat at the outer edges of the flame. Observe the color emitted and record a detailed description in your observation table.
2. Dispose of used splint in the “WASTE” beaker, return the station to condition in which you found it, and move on to the next station.
3. Repeat steps 2 & 3 for the remaining salts. Observe and record the color for each in your table.
4. Obtain a sample of unknown from your teacher. Repeat steps 2 and 3.
5. Continue until you have tested all 3 of the unknowns.
Observations:
Metallic Salt(metals) / Flame Color / Corresponding
Wavelength (nm)
Unknown # 1
Unknown # 2
Unknown # 3
Analysis/Conclusions:
1. What were the identities of the unknowns? How do you know? Please refer to the unknowns by number.
2. Based on your results and observations, would this method be practical to determine metals in a mixture? If not, why not?
3. Give at least two reasons why the flame test may sometimes be invalid.
4. Are flame tests a form of qualitative or quantitative analysis? What other means of qualitative or quantitative analysis can be used to identify metals? Definitions for qualitative and quantitative can be found in your textbook.
5. What are the corresponding wavelengths for the colors observed in this lab? Please place your answers in your observation table.
6. One particular use of these colored flames would be in the design of fireworks. Using the information in your observation table, please design your own firework and then predict what it would look like as it burns!
Recreate the drawing to the right showing how the cylinder of the firework should be filled, and make sure to include an explanation of what a viewer would observe as your firework was set off.
7. Advertising lights (“neon lights”) are produced by sealed tubes of various excited noble gases, which emit colored light. Using internet resources, explain the techniques used in producing these lights. Please paste the link of your resource in your report following your response.
8. Use internet resources to determine the flame color for five additional metal ions. If we have any of these metals in the storage closet, we can certainly try them out in class at a later date! Please paste the link of your resource in your report following your response.