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 [degree]C temperature range. From these data the solubility products (K[subscript sp]), the Gibbs free energies of solution ([Delta][subscript soln]G[degree]), the standard enthalpy of solution ([Delta][subscript soln]H[degree]), and the standard entropy of solution ([Delta][subscript soln]S[degree]) are calculated. Students also determine K[subscript sp] in 0.50 M KCl at room temperature wherein the K[superscript +] concentration is determined by flame emission and HP[superscript -] concentration is determined via titrating with NaOH. In determining both the K[superscript +] and HP[superscript -] concentrations in a saturated solution of KHP in 0.50 M KCl, students verify that K[subscript sp] 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[superscript +] calibration standards from KHP(s). As an additional exercise, students determine the concentration of potassium in Gatorade. (Contains 2 tables.)