Solubility Product Constant Illinois Central （溶度积常数伊利诺斯州中部）.pdfVIP

Page 1 Solubility Product Constant In general, when ionic compounds dissolve in water, they go into solution as ions. When the solution becomes saturated with ions, that is, unable to hold any more, the excess solid settles to the bottom of the container and an equilibrium is established between the undissolved solid and the dissolved ions. For example, when enough calcium oxalate is introduced into solution for it to become saturated, the following equilibrium is established. CaC O Ca+2 + C O 2 2 4(s) (aq) 2 4 (aq) If we write an equilibrium expression for this situation, we obtain: K = [Ca+2][C O 2] sp 2 4 Note that the solid itself does not appear as a denominator in the expression since it is a it is not in the same phase as the aqueous ions. In general, the solubility product constant (Ksp), is the equilibrium constant for the solubility equilibrium of a slightly soluble ionic compound. Like all equilibrium constants, the Ksp is temperature dependent, but at a given temperature it remains relatively constant. It also noteworthy, that, just like any equilibrium expression, each ion concentration in the expression is raised to the power of its coefficient in the solubility equation. For example, the Ksp expression for CaCO3(s) Ca+2 (aq) + CO32(aq) is Ksp = [Ca+2 ][CO3-2] but for the equation PbI2(s) Pb+2(aq) + 2 I 1(aq) Ksp = [Pb+2][I 1]2