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Flame Test Lab - DOC

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					Flame Test Lab

Background:
When atoms absorb energy, the electrons jump to a higher energy state. When
the electrons fall back to the ground state, that energy is released as visible
light. This light can be broken down into a bright line spectrum. Each element
has its own unique bright line spectrum, because the arrangement of electrons in
the atom is unique to each element. In this experiment, we shall use a flame to
give atoms energy, and observe the flame color and bright-line spectrum. We
will then use this data to identify an unknown atom.

Materials:
Beakers with solutions and wooden splints
Spectrometer
Bunsen burner and striker
Inoculating loop
Double cobalt glass square

Procedure:

   1.     On a separate sheet of paper, create a data table with 6 columns and
          14 rows. Label the 3rd, 4 th and 5th boxes of the first row, Trial 1, Trial
          2, Trial 3. Label the SECOND row as follows (in order): metal
          compound, color of flame, wavelength (nm), wavelength (nm),
          wavelength (nm), summary. Label the first column (starting with the
          3rd row): CaCl2 solution, K2SO4 solution, Li2SO4 solution, Na2SO4
          solution, SrCl2 solution, NaCl solution, NaCl crystals, Na2SO4 (cobalt
          glass), K2SO4 (cobalt glass), Na2SO4 and K2SO4, Na2SO4 and K2SO4
          (cobalt glass), Unknown solution.

   2.     Look at the beakers on your lab bench. Be sure you have correctly
          identified each and matched it to the correct row in your data table.

   3.     Obtain and light a Bunsen burner.

   4.     Using ONE of the wooden splints in the beaker labeled CaCl 2 solution,
          hold the splint in the flame. Observe the color of the flame. Take the
          splint out of the flame before it starts to burn, and place it back in the
          solution. Record.

   5.     Obtain a spectroscope. One person should look at the flame through
          the spectroscope while the other holds the wooden splint in the fire.
          Use the same splint as before. Record the bright lines evident.
6.    Repeat step 5, switching places.

7.    If the data is different in step 5 and 6, do the procedure a third time.

8.    Repeat steps 4-7 using the K2SO4 solution, Li2SO4 solution, Na2SO4
      solution, SrCl2 solution, and NaCl solution.
9.    Wet an inoculating loop in distilled water, and place it in the NaCl
      crystals to get some to stick. Hold the NaCl crystals in the flame and
      record your observations. NOTE: you will not use the spectroscope for
      this procedure, so you will not fill in the wavelength portion of the data
      table.

10.   Obtain a double cobalt glass square. Test the Na2SO4 solution in the
      flame, looking at the flame through the cobalt glass. Repeat so both
      partners can observe. Record your observations. NOTE: you will not
      use the spectroscope for this procedure, so you will not fill in the
      wavelength portion of the data table.

11.   Test the K2SO4 solution in the flame, looking at the flame through the
      cobalt glass. Repeat so both partners can observe. Record your
      observations. NOTE: you will not use the spectroscope for this
      procedure, so you will not fill in the wavelength portion of the data
      table.

12.   Test the K2SO4 and Na2 SO4 solution in the flame, without using the
      cobalt glass. Observe and record the flame color. NOTE: you will not
      use the spectroscope for this procedure, so you will not fill in the
      wavelength portion of the data table.

13.   Test the K2SO4 and Na2 SO4 solution in the flame, looking at the flame
      through the cobalt glass. Repeat so both partners can observe.
      Record your observations. NOTE: you will not use the spectroscope
      for this procedure, so you will not fill in the wavelength portion of the
      data table.

14.   Using your knowledge gained through these procedures, test the
      unknown solution. Record your data.

Clean Up

15.   Leave Bunsen burners, strikers, and the solutions on your lab bench.

16.   Return remaining items to the cart in the middle of the room.
   17.   Put all used wood splints into the waste beaker on the cart in the
         middle of the room.

   18.   Wash your hands before returning to your seat.

Questions: (answer separately, DO NOT work with your lab partner).

   1.    Examine your data table, and create a summary for the flame tests for
         each metal ion. Write this summary in the correct place in your data
         table.

   2.    Explain how viewing the flame under the cobalt glass can make it
         easier to analyze the ion being tested.

   3.    Explain how the lines seen in the spectroscope relate to the position of
         electrons in the metal atom.

   4.    What metal ion is in your unknown solution? How do you know?

   5.    How sensitive is the flame test? Could it be used to accurately identify
         metal ions? What difficulty could there be when identifying ions by the
         flame test.

   6.    Explain how you could use a spectroscope to identify the components
         of a solution with several different metal ions in it.

   7.    A student performed a flame test on several unknowns and observed
         that they all were shades of red. What should the student do to
         correctly identify these substances? Explain your answer.

   8.    Fireworks come in a variety of color. Explain how the fireworks
         manufacturers could get these colors.


To Turn in:
   1. Data sheet
   2. Answers to questions

Do not turn in this paper.

				
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