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Flame_Tests_Lab- F11

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					Flame Tests___________________________
Introduction
         According to the Bohr theory of the atom, electrons may occupy only specific energy
levels. When an atom absorbs sufficient energy, an electron can “jump” to a higher energy level.
Higher energy levels tend to be less stable, however, and if a lower energy level is available, the
electron will “fall back”, giving off energy in the process. The difference in energies between the
two levels is emitted in the form of a photon of electromagnetic radiation. The energy of each
photon is described by the equation E = hv, where h is Planck’s constant and v is the frequency of
the radiation. If the wavelength of the released photon is between 400 and 700 nm, the energy is
emitted as visible light. The color of the visible light will depend on the atom’s electron
configuration.
         White light is a continuous spectrum in which all wavelengths of visible light are present.
An excited atom, however, produces one specific line in its spectrum, which is unique to that
element due to its electron configuration.
         Flame tests are a quick method of producing the characteristic colors of metallic ions.
The loosely held electrons of a metal are easily excited in the flame of a Bunsen burner. The color
of the flame produced may be used to determine the identity of the ion.
         In this investigation, you will perform flame tests on several metallic ions, then use your
results to determine the identity of some unknown ions.


Problem

What colors are characteristic of particular metallic ions in a flame test?


Materials

goggles                                   lab apron
gloves                                    well plate
wooden splints                            beaker-50mL
Bunsen burner                             wash bottle
flint striker

solutions of the following salts:
barium chloride (BaCl2)                   copper chloride (CuCl2)
strontium nitrate (Sr(NO3)2)              lithium chloride (LiCl)
potassium chloride (KCl)                  sodium chloride (NaCl)
calcium chloride (CaCl2)                  2 unknown solutions

Safety

        Wear your goggles and gloves at all times during this lab. The HCl is extremely irritating
         to the skin, nasal passages, eyes, and clothing. The salt solutions are toxic, with the
         exception of NaCl. Tie back loose hair and secure loose clothing.
Procedure

   1. Put on your goggles, gloves and lab apron.
   2. Obtain a wooden splint for each sample, flint striker, and Bunsen burner. Light the burner
      using the correct procedure and adjust flame to low.
   3. Wave the wooden splint in the burner flame for a few seconds. Notice the color of the
      wooden splint as it’s heated so that you don’t confuse its color with a flame test. This is
      the color you should see after each test.
   4. Place each pre-soaked wooden splint in the flame and observe. Record your observations
      in the Data Table 1. Allow burned splints to cool on moistened paper towel and repeat
      until you have tested each solution.
   5. Perform flame tests on each unknown solution and record your observations in Data
      Table 2.
   6. Turn off the burner. Clean up your work area.

Data/Results

Data Table 1
                   Salt Solution                                   Color
                      BaCl2
                      CuCl2
                       LiCl
                        KCl
                       NaCl
                      CaCl2
                    Sr(NO3)2

Data Table 2
                Unknown Solution                                   Color
                      #1
                      #2


Analysis/Conslusions

   1. What metallic ions are present in each of the unknown solutions?
   2. Summarize the process that produces the colors seen in the flame tests.
   3. The line emission spectrum of lithium has a red line at 670.8 nm. Calculate the energy of
      the wave.
   4. How do you think metallic salts are used in fireworks?

				
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posted:11/2/2011
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