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Lab: Flame Test Introduction: The normal configuration of the electrons about the atom or ion of an element is called the “ground state”. The electrons of this stable particle are at their lowest possible energy level. However, when these stable particles are heated to very high temperatures, some of the electron leave their ground state and become excited; that is, these electrons move to a higher energy level. They do so by absorbing energy in the form of heat. This excited state is quite unstable and the tendency of these “excited” electrons is to return to their ground state. As these electrons return to the ground state, they release the absorbed heat energy in a different form. Some of this released energy is in the visible region of the electromagnetic spectrum that we see as different colors of light. An excited electron that falls from the 6th energy level down to the 2nd energy level emits a different color of light than an electron falling from the 6th energy level to the 4th energy level. Thus, when heated, metals can emit different colors based on where their ground state electrons “live”. Using colors to identify a metal is called a flame test. Materials: burner 24-well reaction plate Matches modified jumbo pipets holding various known solutions 7 Q-tips unknown solution Cobalt sheet Procedure: 1. Put on goggles and apron 2. Light your burner and properly adjust the flame 3. Soak the end of a Q-tip in a solution of sodium nitrate (NaNO3) 4. Without burning the cotton, passed the soaked end of the Q-tip slowly back and forth through the flame of the burner until there is a color changed in the flame (NOTE: this may require 6 or more passes through the flame) 5. Record the color (make yourself a chart!) 6. Repeat the process with the remaining solutions, including the unknown 7. Repeat steps 3-6 using the cobalt sheet A word of caution…. The flame test’s effectiveness may be limited by contaminants in the solutions, particularly sodium. Sodium is present in many compounds (even though it isn’t on the label!) and can color the flame. Cobalt glass is often used to filter out the yellow color given off by sodium. Name _______________________________ Lab Report Sheet for Flame Test Lab (to answer these questions you will need to reference chapter 10 ) Pledge: 1. Why do the chemists use flame tests? 2. Describe, in terms of electrons, how light is produced in a flame test. Be sure to include the terms ground state and excited state. 3. Is the flame color a test for the metal or for the anion in each solution? _____________. Explain 4. List the ions and their color. Note the data given is not in ion form. Solution ID Ion Flame Color Copper(II)Nitrate Green Barium Nitrate Yellow Green Rubidium Nitrate Deep Red Sodium Nitrate Intense yellow Potassium Nitrate Pale pink-violet Indium nitrate Blue 5a. Which metal ion produced color in the highest-energy range (do not ask Mr. Campbell or Ms. Albach whether it is with or without the cobalt – you figure it out!)? b. Which metal ion produced color in the lowest-energy range? 6. What letter is your unknown? ____A_______ Color : Yellow Green 7. What metal is present in your unknown? _______________. How do you know? 8. What would happen to the color of the flame if you mixed 2 of the solutions together (would the 2 colors mix and become 1 new color or would the two colors be separate)? Explain. 9. Planck’s equation relates the energy of a photon of light to its frequency. E = hv Where Planck’s constant h =6.64 x 10-34 J∙s And frequency (v) is measured in 1/seconds or hertz(Hz) a. If the frequency of a red spectral line is 1.60 x 1014 Hz, how much energy does one photon of this light have? b. If the frequency of a violet spectra line is at 2.50 x 1014 Hz, how much energy does one photon of this light have? 10. The visible light spectrum represents only a small portion of the electromagnetic spectrum. Infrared and ultraviolet radiations lie directly outside the visible range. * UV radiation is dangerous and is located just past the violet region on the spectrum. *IR radition is harmless and is located just before the red region on the spectrum. Based on your calculations in question 9 above, explain why you think UV is more dangerous than IR. 13. If you had two metals that have the same flame color, what additional test could you do to distinguish between them.
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