CHEM 132, Chapter 15

• Solubility


  The ability of a substance to dissolve
• Ionic compounds


  Dissociate when they dissolve
• Molar solubility


  Every ionic compound has a molar solubility and a Ksp
• When solubility is lowered


  Ksp lowers because it is dependent on the number of ions produced upon dissociation
• Ksp


  Dependent only on ionic compound and temperature
• The solubility of ionic compounds


  Is dependent on Ksp
• When solubility is reached


  Q=Ksp
• When Q<Ksp


  The solution is unsaturated, and no precipitate forms
• When Q=Ksp


  The solution is saturated
• When Q>Ksp


  The solution is supersaturated and a precipitate forms
• Ksp value


  Determined from molar solubility which is determined by experiment
• Due to common ion effect


  The solubility of a solid is lowered if the solution already contains ions common to the solid
• If a salt is in equilibrium with its ions and a different salt containing one of the ions already in solution is added

  Equilibrium shifts left, lowering solubility
• pH of a solution


  Can affect a basic salt's solubility
• Addition of OH- ions

  Increases pH, equilibrium is forced left, decreasing solubility
• Addition of H+ ions


  Decreases pH, equilibrium is forced right, increasing solubility
• If anion X- is effective


  Salt MX has increased solubility in acidic solution
• Selective precipitation


  The separation of mixtures of metal ions in aqueous solutions by using a reagent whose anion forms a precipitate with only one or a few of the metal ions in the mixture