Factors Affecting Solubility

pHCommon Ion Effect

Formation of Complex Ions

Common Ion Effect

If one of the ions in a solution equilibrium is already dissolved in the solution, the equilibrium will shift to the left and the solubility of the salt will decrease.

BaSO4(s) Ba2+(aq) + SO42−(aq)

Common Ion Effect Example

• Calculate the solubility of solid CaF2 (Ksp = 4 x 10 -11)

in a 0.025 M NaF solution.

CaF2 (s) Ca +2 + 2 F-

Ksp = 4 x 10-11 = [Ca +2] [ F-]2

pH

– If a substance has a basic anion, it will be more soluble in an acidic solution.• Cl-, I-, Br-

– Substances with acidic cations are more soluble in basic solutions.

pH Example• What is the effect of adding a strong acid on the solubility

of silver acetate?

1. Silver acetate dissolves: AgC2H3O2 (s) Ag+(aq) + C2H3O2

- (aq)

2. Acetate ion combines with H+(aq) ions from strong acid: H+

(aq) + C2H3O2- (aq) HC2H3O2

(aq)

• [Acetate ion] is lowered by adding strong acid to form a weak acid.

• According to Le Chatelier's principle, the solubility equilibrium will shift to the right, causing more silver acetate to dissolve.

Complex Ions• Question: What is a complex ion?• Answer: A metal ion surrounded by ligands

– Metal ions can act as Lewis acids and form complex ions with Lewis bases in the solvent.

More Complex Ions

Ligand = Lewis Base, has lone pair that can be donated to empty orbital on metal to form a covalent bond

Coordination Number(s) of 6,4,2 are most common.

Complex Ions

– The formation of these complex ions increases the solubility of these salts.

Amphoterism

– Amphoteric metal oxides and hydroxides are soluble in strong acid or base, because they can act either as acids or bases.

– Examples of such cations are Al3+, Zn2+, and Sn2+.