Determination of the Solubility Product Constant of a Salt
Date Performed: March 1, 2011
If solid KHC4H4O6 is added to a beaker of water, the salt will begin to dissolve. The amount of solid diminishes, and the concentrations of K+(aq) and HC4H4O6-(aq) in the solution increase. When no KHC4H4O6 dissolves, the concentrations of K+(aq) and HC4H4O6-(aq) will not increase further and any additional KHC4H4O6 added after this point will remain as a solid. At this point, the solution is said to be saturated. The rates at which KHC4H4O6 is dissolving and reprecipitating are equal in a saturated solution, so that no net change is observed. This process is another example of dynamic equilibrium. The equation for potassium hydrogen tartrate dissolving in water is: KHC4H4O6 (s) K+(aq) + HC4H4O6-(aq). For the generalized chemical reaction aA + bB cC + dD, the equilibrium constant expression is keq = [C]c[D]d/[A]a[B]b. The value of the constant that reflects the solubility of a compound is referred to as the solubility product constant, or the ksp. The solubility product constant can be calculated using the equation: Ksp = [k+][HC4H4O6-]. On the other hand, the solubility of a compound refers to the concentration of a solute in equilibrium with undissolved solute in a saturated solution. In this experiment, the solubility and the solubility product constant in water of KHT was determined. The concentration of HC4H4O6- in solution can be determined by the direct titration of a filtered solution with a standard sodium hydroxide solution, since it is a slightly soluble salt. Because one mole of sodium hydroxide neutralizes one mole of HT- ions, the number of moles of sodium hydroxide used in the titration will equal the number of moles of HT-. The concentration of HT- can be determined by dividing its moles by its volume. The concentration of HT- will be equal to the concentration of K+, which in turn will be equal...