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Lab Flame Test for metals

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					Name_____________________________________ Period_____ Date_____



                         Flame Tests for Metals Lab
Purpose
To observe and identify metallic ions using flame tests.

Introduction ; The characteristic yellow of a candle flame comes from the glow of
burning carbon fragments. The carbon fragments are produced by the incomplete
combustion reaction of the wick and candle wax. When elements, such as carbon,
are heated to high temperatures, some of their electrons are excited to higher
energy levels. When these excited electrons fall back to lower energy levels, they
release excess energy in packages of light called photons, or light quanta.
       The color of the emitted light depends on its energy. Blue light is more
energetic than red light, for example. When heated, each element emits a
characteristic pattern of light energies, which is useful for identifying the
element. The characteristic colors of light produced when substances are heated
in the flame of a gas burner are the basis of flame tests for several elements.
In this experiment, you will perform the flame tests used to identify several
metallic elements.

Materials
     5 cotton swabs             5 solutions         pencil or pen
     Goggles                    lab apron           Bunsen burner



Procedure

BEFORE DOING THE LAB, ANSWER THE PRE-LAB QUESTIONS

   1. Obtain the solutions containing the metal ions from your instructor.
   2. Put on the safety gear and light the Bunsen burner.
   3. Dip a cotton swab into the solution you are going to test and then place it in
      the edge of the flame. Note the color of the flame in the data table below.
       NOTE: Don’t leave the cotton swab in the flame long enough to burn it.


   4. Do the same thing for the other solutions.
Pre-Lab Questions:

Answer the following questions to make sure you understand the background
information.

   1.   What did Earnest Rutherford’s gold foil experiment demonstrate about the
        composition of an atom?




   2. What happens to an atom’s electrons when exposed to excess energy?




   3. What is released when an atom’s electrons lose energy and return to its
        ground state?




DATA TABLE

                         Solution           Color when heated
                 Lithium Chloride
                 LiCl
                 Copper Chloride
                 CuCl2
                 Strontium Chloride
                 SrCl2
                 Sodium Chloride
                 NaCl
                 Potassium Chloride
                 KCl
Analyses and Conclusions:


1. Why did different chemicals emit different colors of light?




2. Why do you think the chemicals had to be heated in the flame for the
   colored light to be emitted?




3. Using what you know about wavelengths, frequency, and energy, list the
   metallic elements used in the flame test in increasing order of the energy
   of the light emitted.




4. How does the flame test provide support for quantized energy levels?
   Explain your answer.

				
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posted:3/11/2012
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