The objectives of this lab are to evaluate the temperature dependence of the solubility product constant (Ksp) for potassium hydrogen phthalate (KHP) and to determine whether or not the solubility product is affected by the presence of a “common ion.”
In this experiment, after standardizing a solution of sodium hydroxide, you will titrate several saturated KHP solutions at different temperatures. From the information you gather about the concentration of the hydrogen phthalate ion (HP-) in each solution, you will plot the calculated Ksp for each solution as a function of temperature. This plot will provide the information necessary to determine the standard molar enthalpy of solution, the standard molar entropy of solution, and Gibbs free energy, based on rearrangement of the following equations:
One of the solutions you will titrate will contain potassium chloride (KCl) in addition to KHP. This means that, for this solution, there are two sources of the K+ dissolved in the solution. You are asked to figure out whether or not the presence of a second potassium-containing compound will affect the Ksp of your KHP solution – the “common ion” effect.
In Part A of this lab, you will use the techniques of preparing standard solutions from a stock solution and using the standard solutions to prepare a calibration curve equation, as you did in the second lab this quarter. In this lab, however, you will use a different spectroscopic technique, called atomic emission spectroscopy, in place of the absorbance spectroscopy employed in Lab 2. For Parts B and C, the chemicals and techniques will be familiar to you. Your experience earlier this quarter in titrating KHP with NaOH to the phenolphthalein endpoint will serve you well.