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Ions and Color I - The Color of Ionic Salts Prepared by...

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The Color of Ionic Salts Prepared by Maryann McDermott Jones, University of Maryland, College Park ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) PURPOSE OF THE EXPERIMENT To determine which ion—cation or anion–is responsible for the color of an ionic salt (and the color of the solution it forms) by comparing the color of salts containing the same cation or anion while changing the other. To the identify common features of the electron configuration of colored and colorless ions which account for color. To then devise an approach to using visible light absorption measurements to determine solution concentration. )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) REQUIRED BACKGROUND Students should understand what constitutes an ionic bond and what chemical species exists in aqueous solution when an ionic salt dissolves. Knowledge of the common charge on common ions is essential, as is knowing how to calculate molar concentration. ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) BACKGROUND INFORMATION Visible Light Electromagnetic radiation , such as light in the visible spectrum, has Spectrum properties associated with both waves and particles. When an atom is energized, radiant energy, characteristic of its atomic make-up, is given off in the form of light of a specific wavelength (ex: the characteristic colors of fireworks produced by ionizing metal atoms with explosives). The energy of a discrete unit ( quantum ) of radiant energy is related to the wavelength (the distance from one wave peak to the next) and frequency (the number of waves passing a given point in some fixed time) of visible light: higher frequencies and shorter wavelengths are associated with higher energy radiation, while lower frequencies and longer wavelengths correspond to lower energy. The colors observed for various ions in solution reflect the energy of the valence electron shell of those ions. )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) PROCEDURE CAUTION : Wear departmentally approved safety goggles while doing this experiment )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) NOTE: Record all data in your lab notebook . Reproduce the Data Form at the end of the experiment in the notebook. You will neatly copy that data onto the sheet included in the protocol to submit with the report. Sloppy forms with scratched-out data will not be graded. ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) Students will work and gather data in teams of four.
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I SALT AND SOLUTION COLOR During this part of the experiment, students must gather data from at least one other team about the set of salts and solutions they observe; ideally the class would share and compare data from four sets of salts. 1. The TA will assign to each team to study one of the sets of four salts which appear in Table 4.1 . Table 4.1 Ionic Salts to Test for Solution Color (0.10 M) Group I lithium nitrate, zinc nitrate, copper (II) nitrate, copper (II) sulfate Group II sodium nitrate, strontium nitrate, nickel nitrate, nickel chloride Group III potassium nitrate, barium nitrate, cobalt (II) nitrate, cobalt chloride Group IV magnesium nitrate, aluminum nitrate, iron (III) nitrate, iron (III) chloride 2. Use a clean, dry scoopula to place a small sample (~0.02 g, just enough
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