Flame Test Lab

Flame Test Emission Spectroscopy Mr. Bartelt’s Chemistry Class

I. Introduction If an element can be placed in solution and that solution aspirated into (sucked into) a burning flame, the element's electrons will absorb energy. This process is sometimes called "exciting" the electrons. As those electrons then return to their normal or “ground” state, energy is emitted in the form of electromagnetic radiation. Simply stated: if you excite, via heat, a metallic electron, that electron will become excited and emit light as it returns to its ground (non-excited) state. Every element emits a unique characteristic light. Just as a fingerprint is unique to each person, the color of light emitted after excitation of an element is unique to that element. Only a few elements give off a characteristic light in the visible region of the spectrum. The visible region of the spectrum is that which is visible to the human eye. For most elements the characteristic frequencies are detectable only in the ultraviolet or infrared region of the spectrum. The emission of a characteristic color (electromagnetic radiation) as the excited electron returns to its ground state provides remarkable tools to analytical chemists (e.g., emission spectrograph, quantometer, flame spectrophotometer, etc.). In a crude way, you will be replicating the process used in these very sophisticated instruments. Barium, calcium, lithium, potassium, sodium, and strontium are examples of elements that display a characteristic light in the visible region of the spectrum. These metallic ions can be identified via the flame test. II. Objective: • To excite selected substances and observe the characteristic emission spectra. • To identify substances by their color emission.

Caution: We will be working with flammable liquids in lab today. There is to be not horse play or practicle jokes. Safety goggles and a lab apron are to be worn at all times while not observing through the spectroscope. NOTE: The evaporating dishes will be housing an alcohol flame. This makes the evaporating dish quite hot. DO NOT TOUCH THE EVAPORATING DISH WITH YOUR HANDS AFTER IT HAS BEEN ON FIRE!

Materials Needed: Evaporating dish and compounds (LiCl, NaCl, KCl, CaCl2, CuCl2) Laboratory burner Graduated cylinder, 50 mL or 100 mL Stirring rod, spatula, and tongs Bunsen burner, flint lighter II. Procedure: 1. Obtain the first sample of from your instructor. 2. Place a small amount of your sample in an evaporating dish using a spatula. 3. Add 25-50 mL of ethanol (denatured so if you drink it you go blind) to the evaporating dish. 4. Using a clean stirring rod, carefully stir the solution until as much of the solid as possible has dissolved. 5. When you are told, ignite your Bunsen burner. 6. Use your Bunsen burner to ignite the alcohol. 7. Wait approximately 30 seconds for the flame to begin emitting the substance’s characteristic light. At this point the lights will be turned off. 8. Observe the flame and record color of the line on the worksheet provided. Be sure to label the substance observed and the color of the flame produced (e.g. Ba2+ Green/Yellow). Additionally, record any other observations about the sample that you feel might be important. Describe the way it burns, or how the flames behave or anything else that seems peculiar or unusual. 9. Repeat steps 1-8 for every sample. III. Data/Results

Sample LiCl NaCl KCl CaCl2 CuCl2

Color emitted/ observations

Questions to be addressed in the conclusion 1. What color flame did each sample produce? 2. Why are different colored flames produced?