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2007
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In the Laboratory
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Flame Emission Spectrometry in General Chemistry Labs: Solubility Product (Ksp) of Potassium Hydrogen Phthalate
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Frazier W. Nyasulu, William Cusworth III, David Lindquist, and John Mackin
Department of Chemistry, University of Washington, Seattle, WA 98195-1700
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March 2007
Vol. 84 No. 3
p. 456
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| Abstract |
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In this general chemistry laboratory, flame emission spectrometry is used to determine the potassium ion concentration in saturated solutions of potassium hydrogen phthalate (KHP) in the 0–65 °C temperature range. From these data the solubility products (Ksp), the Gibbs free energies of solution (ΔsolnG°), the standard enthalpy of solution (ΔsolnH°), and the standard entropy of solution (ΔsolnS° are calculated. Students also determine Ksp in 0.50 M KCl at room temperature wherein the K+ concentration is determined by flame emission and HP- concentration is determined via titrating with NaOH. In determining both the K+ and HP- concentrations in a saturated solution of KHP in 0.50 M KCl, students verify that Ksp is a constant by showing that the same numerical values are obtained, with and without KCl. This experiment also addresses one of the serious problems we and many others have noticed; students do not know how to prepare solutions accurately, especially dilute solutions. We therefore require our students to prepare the K+ calibration standards from KHP(s). As an additional exercise, students determine the concentration of potassium in Gatorade.
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| Supplement |
Student handouts, notes for the instructor, and an example of a postlab report are available.
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| More Information |
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Citation |
Nyasulu, Frazier W.; Cusworth, William, III; Lindquist, David; Mackin, John. J. Chem. Educ. 2007 84 456.
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Keywords |
Acids / Bases; Atomic Spectroscopy; Equilibrium; First-Year Undergraduate / General; Hands-On Learning / Manipulatives; Laboratory Instruction; Physical Chemistry; Quantitative Analysis; Spectroscopy; Thermodynamics; Titration / Volumetric Analysis
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History |
Created:
Last Updated: |
2/1/2007
2/16/2007
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 Caution! | | Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations. |
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456
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