Solubility Equilibria
Name ________________
Chem Worksheet 18-7
Ionic solids that are described as insoluble or slightly soluble can be described using the concept of
equilibrium. An insoluble solid reaches a state of equilibrium with its dissolved ions when there are very
small amounts of ions present. The solubility equilibrium equation for an insoluble ionic compound is
written below. The forward reaction is shows the dissolution of Ni(OH)2 into nickel (II) and hydroxide
ions while the reverse reaction shows the precipitation of Ni(OH)2 from the ions.
Ni2+ (aq) + OH– (aq)
Ni(OH)2 (s)
This equation has a very small equilibrium constant. In other words, an equilibrium is reached when the
reaction has produced a very small concentration of dissolved ions. The amount of the nickel (II) hydroxide
compound that dissolves is described as the molar solubility of the compound.
Example
What is the molar solubility of silver carbonate, Ag2CO3, given that it has a Ksp = 6.3 × 10-12.
- Write the solubility equilibrium equation:
- Write the solubility product expression:
- Create a table to organize concentrations:
2Ag+ (aq) + CO32– (aq)
Ag2CO3 (s)
Ksp
Ag2CO3 (s)
initial
change
equil.
- Substitute equilibrium concentrations and solve:
(solubility)
x
= [Ag+]2[CO32–]
2Ag+ (aq) + CO32– (aq)
0M
0M
+ 2x
+x
2x
x
Ksp
= [Ag+]2[CO32–]
-12
6.3 × 10
= (2x)2(x)
-12
6.3 × 10
= 4x3
x (solubility) = 1.1 × 10-4 mol/L
Solve the following equilibrium problems. Show all work and report answers with units.
1. Write the solubility equilibrium equation for
calcium sulfate, CaSO4.
2. Write the solubility equilibrium equation for
magnesium hydroxide, Mg(OH)2.
3. Write the solubility product expression for
strontium carbonate, SrCO3.
4. Write the solubility product expression for
copper (II) phosphate, Cu3(PO4)2.
5. What is the molar solubility of silver bromide,
AgBr, at 25ºC? (Ksp = 5.0 × 10-13)
6. What is the molar solubility of tin (II)
hydroxide, Sn(OH)2, at 25ºC? (Ksp = 1.4 × 10-28)
7. A sample of lead (II) carbonate, PbCO3, is
added to water at 25ºC. At equilibrium the
concentration of lead (II) ions is 2.7 × 10-7 M.
What is Ksp for PbCO3?
© John Erickson, 2005
8. A sample of aluminum hydroxide, Al(OH)3,
is added to water at 25ºC. At equilibrium the
concentration of Al3+ ions is 2.6 × 10-9 M.
What is Ksp for Al(OH)3?
9. What are the equilibrium concentrations of
Mg2+ and CO32- in a saturated solution of
magnesium carbonate, MgCO3, at 25ºC?
(Ksp = 3.5 × 10-8)
10. What are the equilibrium concentrations of
Ag+ and CrO42- in a saturated solution of
silver chromate, Ag2CrO4, at 25ºC?
(Ksp = 1.1 × 10-12)
11. What are the equilibrium concentrations of
Pb2+ and AsO43- in a saturated solution of lead
(II) arsenate, Pb3(AsO4)2, at 25º?
(Ksp = 4.0 × 10-36)
WS18-7SolubilityEquilibrium