Name:______________________________________________________________________________ Flame Test Lab (Unit 3.3 and 3.4) Background: When an element is heated, the electrons will be excited. Then as these electrons fall back from one energy level to another, they will emit photons of light. These photons will have different colors depending on the element and its discrete energy levels. That is, different wavelengths of light (colors) will be emitted when the electrons of different elements go down the step(s) between their energy level(s). Each element will have its own set of steps; therefore each will have its own color or set of colors. Compounds containing elements in Group I and II of the Periodic Table can be identified by the colors they emit. The spectrum of the flame of each element consists of certain colors— wavelengths—characteristic of that element. These lines are a characteristic of an element as fingerprints are of an individual person. No two elements give the same bright line spectrum. Spectral lines are the result of energy changes in the electrons of the atoms. When an atom from a metal element is heated, its electrons become excited, that is, their energy is increased. Excited electrons soon lose the energy they have gained. This energy is lost in the form of light, called photons. A photon is an individual packet of light having a specific wavelength. Certain wavelengths of light are visible to humans and can be seen as different colors. By observing the color of light emitted from heating a metal solution, its visible light spectrum can be seen, and thus, its identity can be determined. Today you will be heating various salts (compounds containing various metals bonded to non-metals) and observing the emission colors they produce. This test is an example of how scientists use emission spectra to identify different elements based on Bohr’s model. Procedure: 1) Scoop a small amount of each salt in separate wells of your spot plate. Record which salt you put in each well. 2) Light your Bunsen burner. (Once it is lit, either you or your lab partner must stay with it at all times.) 3) Put a small amount of one salt on the inoculating needle and burn in the blue cone shaped area of the flame. (You may need to do this several times to see the full spectrum.) 4) As the flame burns use the spectroscope to view the line emission spectra of the salt. Record the color you see with the naked eye as well as the bands of color you see in the spectroscope in the table on the next page. 5) Repeat steps 3 and 4 for each salt. Be sure to test Sodium Chloride (NaCl) last. Name:______________________________________________________________________________ Salt Color of flame produced Emission bands produced Barium Chloride BaCl2 Lithium Chloride LiCl Potassium Chloride KCl Strontium Nitrate Sr(NO3)2 Copper (II) Nitrate Cu(NO3)2 Lead Nitrate Pb(NO3)2 Copper Sulfate CuSO4 Unknown Substance Sodium Chloride NaCl Questions: 1) What inaccuracies (errors) may be involved in using flame test for identification purposes? 2) Why do the different compounds produce different wavelengths of light when heated? Be specific about what is happening to the electrons of the atom. 3) The energy of colored light increases in the order of red, orange, yellow, green, blue, indigo and violet. List the metallic elements used in the activity in order of increasing energy emitted (lowest to highest). 4) Why do you think the chemicals have to be heated in the flame before the colored light is emitted?