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Flame Tests of Metal Ions -- Chemistry Laboratory Purpose: To discover the different frequencies of light that is emitted by various metallic ions. Pre Lab Questions: Electromagnetic spectrum 1. What are the colors of light in the visible spectrum in order of increasing energy (decreasing wavelength)? 2. Define atomic emission spectrum. 3. Define ground state 4. Define Photon 5. How can electrons become excited? 6. What generally happens when electrons loose extra energy? Background information: Using your text book and the handout include information about the electromagnetic spectrum. Make sure to include information about the color of light in the visible spectrum, the energy of the light, and how the light is produced. Safety: Follow appropriate safety procedures when operating the burners. Tie back long hair and secure loose clothing. Many of the salts used in this experiment are toxic. Be sure to wash hands thoroughly after coming into contact with any of the substances. Materials Metal Salts 10 metal salts (s) Unknown (a mixture of 2 or more of the above salts) Equipment Bunsen Burner Striker Cotton Swab Beaker of water Procedure: 1. You will be rotating through 7 different stations in a clockwise direction. You will have no more than 4 minutes at each station. 2. If the burner is not lit, follow the appropriate procedures for lighting the burner. Pick up a correctly labeled cotton swab or paperclip loop. 3. Dip the wire loop into the beaker of distilled water. Then dip the wire loop into the beaker of metal salt crystals so that a FEW crystals adhere to the loop. Don’t pick up too many crystals or the will make a mess! Remember, some of these are toxic and we do not want crystals lying around the station to get onto your skin or into your eyes. 4. Place the wire loop into the burner flame. Observe the color produced and record it in a table you construct. Watch carefully because some colors will not last long. Be as descriptive as possible. (e.g. red orange instead of orange) 5. Rotate to the next station. DO NOT LEAVE THE FLAME UNATTENDED. If another group is ready to use your station, you may leave the flame in their care. Otherwise, extinguish the flame by turning off the gas before leaving your station. 6. Repeat steps 1-5 until you have observed all six metal salts and the unknown. Observations: Record you observations as directed in the procedure. You will need to create a table to make your observations on similar to the one shown below: Element No. 1 Metal Salt Strontium Chloride, SrCl2 Detailed Observations Post Lab Questions: What is the unknown metal ion? Describe what evidence you have to support your answer. Explain how colors are produced by the metal ions. Include terms such as ground state, excited state and photon in your explanation. Explain how a forensic scientist could use similar methods to determine an unknown substance at a crime scene. List the electron configurations for the metal ions used in the compounds you tests. You may use the noble gas configurations if you would like. Draw the orbital box diagram for each. Atomic Spectrum The Atomic Spectrum is a series of lines of color produced when light from an excited atom is passed through a prism. It is also known as a line spectrum. Each element has its own unique atomic spectrum and address. Because of their unique nature, atomic spectra are also referred to as the "fingerprints of the elements." The series of lines of color that an atom will produce is related to the locations of the electrons on that atom and their relationship with the nucleus. Atomic spectra were fundamental pieces of experimental information used by chemists in the development of the electronic structures of atoms. By studying the colors emitted by the different elements, it is possible to work backwards to the sources of those colors. In this way it is possible to determine the electronic structures of the elements. Most of the basic information known today about electronic structures was derived from studying the light emitted by the atoms. The process of exciting an atom, involves adding energy to the atom. This can be done in a variety of ways. Simply heating a sample of an element up in an open flame will excite electrons. Passing electricity through a sample of an element will excite electrons. The colored lights observed when sky rockets explode are a result of burning gunpowder exciting electrons within atoms of elements packed with the gun powder. Electromagnetic Radiation Spectrum The Electromagnetic Radiation Spectrum, or EMR Spectrum, is a full "rainbow" of all colors of light, both visible and non-visible. To a large degree it is a theoretical spectrum, in that no real system is capable of producing all colors of emr. The EMR Spectrum is generally broken down into three regions--visible, ultraviolet and infrared. By tradition, the spectrum is shown with the colors in order of increasing wavelengths, decreasing frequencies and decreasing energy values. Energy Level An energy level is a specific location on an energy level diagram that corresponds to an allowed specific energy content of an electron. Bohr Theory said that the electron was restricted to existing only at specific levels of energy and would never be found with energy content between those levels. This component of the theory was based on work done by Max Planck. Excited State The Excited State according to Bohr Theory is a position on an energy level diagram that contains more energy than the Ground State. When an electron is exposed to energy it may absorb some of that energy. If it does, it will rise up the energy level diagram to a new position that corresponds to the higher energy content. An electron in an excited state is not in its most stable position. An electron in an excited state will eventually return to the Ground State. Electron Transition An electron transition is the movement of an electron from one energy level to another. If an electron moves from a low energy level to a higher energy level it does so by gaining energy. If it moves from a higher energy level to a lower energy level, it does so by releasing energy. The released energy is in the form of electromagnetic radiation. The energy content and wavelength of the released electromagnetic radiation will correspond to the difference in energy content of the two levels. This transition is also known as a Quantum Jump.