Download III. Solubility Equilibria Solbility and Equilibrium

III. Solubility Equilibria
Solbility and Equilibrium
- solubility: the amount of solute that will dissolve in a solvent at a given temperature to form a saturated solution
- if a solution becomes saturated, then a solubility equilibrium results
- in a solubility equilibrium, the rate of dissolving is equal to the rate of crystallization
ex. NaCl (s) U Na+ (aq) + Cl- (aq)
- a solute with high solubility will result in an equilibrium that favours the products; a solute with low solubility will result in an
equilibrium that favours the reactants
- the extent to which the equilibrium favours the products is described by the solubility product constant
The Solubility Product Constant, Ksp
- the equilibrium constant for solubility reactions is Ksp
ex. BaSO4 (s) U Ba2+ (aq) + SO42- (aq)
Ksp = [Ba2+][ SO42]
ex. Write the solubility equilibrium and Ksp expression for the following solutes.
(1) CaCO3
(2) PbCl2
(3) aluminum hydroxide
Calculations Involving Ksp
ex. What is the concentration of S2- ions present in a saturated solution with [Co2+] = 0.020 M.
(cobalt (II) sulphide has Ksp = 5.0x10-22)
ex. What is the concentration of CO32- ions present in a saturated solution with [Ag+] = 0.050 M.
(silver carbonate has Ksp = 8.1x10-12)
ex. The solubility for silver bromide is 8.8x10-7 M. Determine Ksp.
(note: at equilibrium, there will be no excess solid remaining)
ex. The solubility of iron (II) hydroxide is 1.4x10-3 g/L. Determine Ksp.
ex. The Ksp for cobalt (II) sulphide is 5.0x10-22. Determine the solubility. What is the concentration of each ion at equilibrium?
ex. The Ksp for copper (II) iodate is 1.4x10-7. Determine the solubility. What is the concentration of each ion at equilibrium?
Relative Solubilities
- if solutes dissolve to give the same number of ions, the solute with the highest Ksp will have the highest the solubility
ex. rank the following substances from highest to lowest solubility.
CuI (Ksp = 5.0x10-12)
CaSO4 (Ksp = 6.1x10-5)
AgI (Ksp = 1.5x10-16)
- if the solutes dissolve to give different numbers of ions, the solubility must be calculated from the Ksp.
ex. rank the following substances from highest to lowest solubility.
Ag2S (Ksp = 1.6x10-49)
CaS (Ksp = 8.5x10-45)
Bi2S3 (Ksp = 1.1x10-73)
Common Ion Effect
- the common ion effect describes the decrease in solubility that results from dissolving a solute in a solvent that contains one of the
ions in the compound
ex. What is the solubility of calcium fluoride (Ksp = 3.9x10-11) in a 0.100 M solution of sodium fluoride in mol/L?
ex. What is the solubility of magnesium fluoride (Ksp = 6.4x10-9) in a 0.200 M solution of magnesium nitrate in mol/L? What is the
solubility in g/L?
Determining if a Precipitate will Form
- if two solutions are mixed, a precipitate will form if ion concentrations are high enough
- to determine if ion concentrations are high enough, a Q value must be calcualted
- if Q>K, ion concentrations are high enough for a precipitate to form; if Q<K ion concentrations are NOT high enough for a
precipitate to form
ex. Will a precipitate form if 20.0 mL of 0.010 M CaCl2 is mixed with 20.0 mL of 0.080 M Na2SO4?
ex. Will a precipitate form if 150.0 mL of 0.0100 M Mg(NO3)2 is mixed with 250.0 mL of 0.100 M NaF? Calculate [Mg2+] and [F-] at
equilibrium.
Selective Precipitation
ex. A solution contains 1.0x10-4 M Cu+ and 2.0x10-3 M Pb2+. If I- is gradually added to the solution, will PbI2 (Ksp = 1.4x10-8) or CuI
(Ksp = 5.3x10-12) precipitate first. What concentration of I- is necessary to precipitate each salt?
Complex Ions
Complex ion: a charged species consisting of a metal ion surrounded by ligands
Ligands: ions or molecules that bond to a metal ion. Common ligands include Cl-, F-, CN-, OH-, NH3, and H2O
Coordination Number: the number of ligands that surround a metal ion. In general, the coordination number can be determined by
doubling the charge on the metal ion.
Complex Ion Reactions
In general, in order to form a complex ion, the metal must be combined with a concentrated solution of the ligand.
ex. A concentrated solution of sodium hydroxide is added to a solution of solid zinc nitrate
ex. An excess of ammonia is added to silver nitrate solution
ex. Excess hydrochloric acid is added to a solution of aluminum nitrate