1. Solubility
Physical Equilibria

2. OUTCOME QUESTION(S):
C PREDICTING EQUILIBRIUM
Use the value of the reaction quotient, Q to explain how far a system at equilibrium has gone towards completion.
Write solubility product (Ksp) expressions from balanced chemical equations for salts with low solubility and solve related problems.
Vocabulary & Concepts
Dissociation Ionization Saturate

3. These next 3 slides should be a review of grade 11…
There are 3 actions that affect solubility:
These next 3 slides should be a review of grade 11…
1. Nature of the solute / solvent “like dissolves like”
Polar / ionic (charged) solutes dissolve in polar solvents
Non-polar (uncharged) solutes dissolve in non-polar solvents
2. Temperature
Solids placed in liquids: ↑ temperature - ↑ solubility
Gases placed in liquids: ↑ in temperature - ↓ solubility
3. Pressure
Does not affect the solubility of (s)/(l)
For gases (g): ↑ pressure ↑ solubility

4. Aqueous (aq) phase means “dissolved in water”
Dissolving: whole particles separate in solution
Any solute that is soluble, will dissolve to some degree
Following “like dissolves like” rule
C6H12O6(s) C6H12O6(aq)
Aqueous (aq) phase means “dissolved in water”
SOLVENT
Dissociating: particles disperse as individual ions
Only ionic and highly polar compounds
Ions (charged particles) create electrolyte solutions
NaCl(s) Na+ (aq) Cl-(aq) – + – + – + + – + – – + – + + – + –
SOLUTE
HCl(l) H+ (aq) Cl-(aq)

5. AaBb aA+(aq) + bB¯(aq) AgCl (s) Mg(OH)2 (s) Ag+(aq) + Cl¯(aq)
This is a general ionization/dissociation equation:
AaBb aA+(aq) + bB¯(aq)
silver chloride:
AgCl (s)
Ag+(aq) + Cl¯(aq)
If you can build the compound, reverse engineer it - what are the parts of the compound? Break it up as ions
magnesium hydroxide
Mg(OH)2 (s)
Mg2+(aq) + 2 OH¯(aq)
lead (II) phosphate
Pb3(PO4)2 (s)
3 Pb2+(aq) + 2 PO43-(aq)

6. Ksp Ksp = [A+]a[B-]b = AaBb(s) aA+(aq) + bB¯(aq)
Equilibrium will be reached for a saturated solution at a constant temperature:
AaBb(s) aA+(aq) + bB¯(aq)
Remember: solids and liquids are incorporated into the constant value
Ksp =
[A+]a[B-]b
{AaBb}
Ksp = [A+]a[B-]b
Ksp, called the solubility product constant.

7. Remember to look out for volume values and unit irregularities
At equilibrium, the [Ag+] = 1.3 x 10-5 M and the [Cl-] = 1.3 x 10-5 M, find the Ksp of silver chloride?
AgCl (s)
Ag+(aq) + Cl-(aq)
Remember to look out for volume values and unit irregularities
Ksp = [Ag+][Cl-]
Ksp =(1.3 x 10-5)(1.3 x 10-5)
Think about why these two concentrations are the same (remember ICE tables)
Ksp = 1.7 x 10-10

8. Ksp = [Pb+2][Cl -]2 Ksp = [1.62 x 10 -2][ 3. 24 x 10 -2]2
Calculate Ksp of lead (II) chloride if a 1.0 L saturated solution has of lead ions.
1.62 x 10-2
1.62 x 10-2 M
PbCl2 (s) Pb2+ (aq) Cl1- (aq) 1 1
[I]
(solid - doesn’t matter) X
[C]
- x
+ x
+ 2x
[E]
2(1.62 x 10-2)
In a saturated solution ALL solute has dissolved – in all cases – making this more of a Type III problem
Ksp = [Pb+2][Cl -]2
Ksp = [1.62 x 10 -2][ x 10 -2]2
Remember: the coefficient 2 creates the (2x) and also is the power ([ ]2)
Ksp = 1.70 x 10-5

9. This is a “reverse” question
Ksp of magnesium hydroxide is 8.9 x What are the [equilibrium] of ions in saturated solution?
Mg(OH)2 (s)
Mg2+(aq) + 2 OH¯(aq)
[I] x
-x +x x
x x
[C]
[E]
1.3 x x 10-4
Ksp = [Mg2+][OH-]2
This is a “reverse” question
8.9 x = 4x3
8.9 x = [x][2x]2 4 4
8.9 x = [x]4x2 3√ 3√
2.23 x = x3
8.9 x = 4x3
1.3 x 10-4 M = x

10. First change into mol/L – need dimensional analysis and the molar mass
The solubility of PbF2 is What is the value of the solubility product constant?
0.466 g/L
PbF2(s) Pb2+(aq) + 2 F¯(aq)
(19) = 245g/mol
Ksp = [Pb2+][F-]2
First change into mol/L – need dimensional analysis and the molar mass
0.466 g
1 mol =
1.90 x 10-3 M PbF2
1 L
245.2 g

11. PbF2(s) Pb2+(aq) + 2 F¯(aq)
[I]
1.9 x 10-3 M
[C]
- x
+ x
+ 2x
[E]
1.9 x 10-3 M
3.8 x 10-3 M
In a saturated solution ALL solute has dissolved ~
The original concentration is the final concentration (for 1:1)
Ksp = [Pb2+][F-]2
Ksp = (1.90 x 10-3)(3.80 x 10-3)2
Ksp = 2.74 x 10-8

12. Predicting Precipitation

13. Compare Q value with given Ksp to determine if solution is saturated / unsaturated / supersaturated
1. Q = Keq Solution is at equilibrium.
Qc =
[A+]a[B¯]b
Solution is saturated
2. Q < Keq Solution is NOT at equilibrium.
Qc =
[A+]a[B¯]b
Solution is unsaturated
More solute can dissolve
3. Q > Keq Solution is NOT at equilibrium.
Qc =
[A+]a[B¯]b
Solution is supersaturated
Some solute left undissolved

14. CAN YOU / HAVE YOU?
C PREDICTING EQUILIBRIUM
Use the value of the reaction quotient, Q to explain how far a system at equilibrium has gone towards completion.
Write solubility product (Ksp) expressions from balanced chemical equations for salts with low solubility and solve related problems.
Vocabulary & Concepts
Dissociation Ionization Saturated