Flame Emission Spectrometry in General Chemistry Labs: Solubility Product (Ksp) of Potassium Hydrogen Phthalate.

• Autores: Frazier Nyasulu, William Cusworth III, David Lindquist, John Mackin
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 84, Nº 3, 2007, págs. 456-458
• Idioma: inglés
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• Resumen

  • 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 (?solnG°), the standard enthalpy of solution (?solnH°), and the standard entropy of solution (?solnS° 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.