Associated with any ionic compound is the solubility product constant, which measures how soluble the compound will be in a solvent.
Concept #1: Understanding the Solubility Product Constant.
The general rule is that the greater the solubility product constant for a compound then the more soluble the compound.
Example #1: Consider the following compounds. Which has the highest concentration of OH- ions?
a) Co(OH)2 Ksp = 1.3 x 10-15
b) Cu(OH)2 Ksp = 2.2 x 10-20
c) Ni(OH)2 Ksp = 6.0 x 10-16
d) Fe(OH)2 Ksp = 4.1 x 10-15
e) Zn(OH)2 Ksp = 3.0 x 10-16
Example #2: The solubility of silver sulfate, Ag2SO4, is 0.025 M at 25oC. Calculate its solubility product constant, Ksp.
Whenever the question refers to the solubility then that value represents our “x” variable.
Example #3: Find the solubility of CoCl3 (Ksp = 2.8 x 10-13) in:
a) pure water
Whenever we deal with the solubility product constant we use an ICE Chart and since the reactant will always be a solid then we can ignore it.
If our compound dissolves in a solution with similar ions then the Common Ion Effect takes place.
Example #4: Find the solubility of CoCl3 (Ksp = 2.8 x 10-13) in:
b) 0.20 M NaCl.
Example #5: What is the molar solubility of Fe(OH)3 (s) in a solution that is buffered at pH 3.50 at 25 oC? The Ksp of Fe(OH)3 is 6.3 x 10–38 at 25 oC.
Example #6: Find the pH of a saturated solution of Aluminum hydroxide, Al(OH)3. The Ksp of Al(OH)3 is 1.9 x 10-10.
Example #7: Will a precipitate form when 0.150 L of 0.100 M Pb(C2H3O2)2 and 0.100 L of 0.20 M KCl are mixed? The Ksp value of PbCl2 is 1.2 x 10-5.
Example #8: Two flasks containing 7.12 x 10-6 M silver nitrate, AgNO3, and 8.33 x 10-4 M strontium bromide, SrBr2 respectively, are mixed together into a larger flask. If the Ksp of silver bromide, AgBr, is 5.35 x 10-13 what will happen?
Example #9: A saturated solution of AlCl3 contains 5.15 x 10-4 M chloride ions. What is the solubility product constant, Ksp?
Example #10: Molar Solubility of Ions
Example #11: The solubility of CaF2 is 53.2 g/mL at 25 oC. Calculate its solubility product constant, Ksp.
Example #12: The concentration of chloride and iodide ions present in the solution are [Cl –] = 0.073 M and [I –] = 0.060 M. The use of silver, Ag, can be used to precipitate these two ions. If the Ksp value of AgCl is 1.77 x 10-10 and AgI is 8.51 x 10-17.
a) Which ion will precipitate out first?
b) At what concentration will this ion from Part A begin to precipitate out?