solubility and complex-ion equilibria

solubility

the concentration at the point of saturation in a solution; precipitation and dissolution occur at the same rate

solubility product constant

Ksp; constant for the equilibrium established between a solid solute and its ions in saturated solution

molar solubility

the number of moles of solute that can dissolve in one liter of solution at equilibrium

Ksp formula

Ksp = [A^m+]^x[B^n-]^y where Am+ and Bn- are the concentrations of the ions in a saturated solution, and x and y are their respective coefficients in the balanced dissolution equation.

when do you use molar solubilities instead of Ksp?

when comparing solubilities of different substances with different cation-anion ratios in a mixture or solution.

solubility and common ion effect

The common ion effect describes the decrease in solubility of a salt when a common ion is added to the solution. This occurs because the presence of the common ion shifts the equilibrium, reducing the solubility of the original salt.

salt effect

The salt effect refers to the change in solubility of a solute when salts are added to the solution. This effect is due to ionic interactions in the solution between the solution and the added ions which are different than those directly involved in the solution equilibrium, which can alter the solubility equilibrium.

incomplete dissociation

due to ion pairs forming in solution, leading to lower concentrations of free ions than expected.

ion pair

association of cation and anion in solution; effective concentrations decrease, solubility increases, so equilibrium shifts to right to increase ion concentrations

ion product Qsp vs. Ksp

• Qsp > Ksp : precipitate will form until Qsp = Ksp

• Qsp = Ksp : equilibrium exists and solution is saturated

• Qsp < Ksp : solute will dissolve until Qsp = Ksp

fractional precipitation

A technique used to separate ions from a solution by adding a reagent so that one ion precipitates out while others remain dissolved.