Solubility Equilibria

• Write solubility product (Ksp) expressions from balanced chemical equations for salts with low solubility.

 • Solve problems involving Ksp.

Additional KEY TermsDissociation Saturated

C6H12O6(s) C6H12O6(aq)

There are 3 actions that affect solubility:

1. Nature of the solute and solvent“like dissolves like”

Polar / ionic solute dissolve in polar solvent.Non-polar dissolve in non-polar.

Even the most insoluble ionic solids are actually soluble in water to a limited extent

2. Temperature

Solids in liquids: ↑ temperature - ↑ solubility.Gases in liquids: ↑ in temperature - ↓ solubility.

3. Pressure

Does not affect the solubility of (s)/(l).(g): ↑ pressure ↑ solubility.

AaBb(s) aA+(aq) + bB¯(aq)

Ksp, called the solubility product constant.

Ksp = [A+]a[B-]b

Product of ion concentrations in a saturated solution.

Kc =

[A+]a[B-]b [AaBb]

Write the dissociation and the product constant equation for the solubility of calcium hydroxide.

Ksp = [Ca2+][OH-]2

Ca(OH)2 (s)

Pb3(PO4)2(s) 3 Pb2+(aq) + 2 PO4

3-(aq)

Ksp = [Pb2+]3[PO43-]2

Write a solubility product expression for Pb3(PO4)2.

Ca2+(aq) + OH-

(aq)2

At equilibrium, the [Ag+] = 1.3 x 10-5 M and the [Cl-] = 1.3 x 10-5 M, what is the Ksp of silver chloride?

Ksp = [Ag+][Cl-]

Ksp =(1.3 x 10-5)(1.3 x 10-5)Ksp = 1.7 x 10-10

AgCl (s) Ag+(aq) + Cl-

(aq)

*NOTE: Ksp has no units.

SolubilityAnd

I.C.E. Tables(Yeah!)

Calculate Ksp of lead (II) chloride if a 1.0 L saturated solution has of lead ions.

I --- 0 0C -x +x +2xE 0

Ksp = [Pb+2][Cl -]2

Ksp = [1.62 x 10 -2][ 3. 24 x 10 -2]2

Ksp = 1.70 x 10 -5

PbCl2(s) Pb2+(aq) + 2 Cl-

(aq)

1.62 x 10-2 M

2(1.62 x 10-2)

1.62 x 10-2 M

The solubility of PbF2 is . What is the value of the solubility product constant?

PbF2(s) Pb2+(aq) + 2 F¯(aq)

0.466 g1 L 245.2 g

1 mol= 1.90 x 10-3 M PbF2

0.466 g/L

207 + 2 (19) = 245g/mol

Ksp = [Pb2+][F-]2

Ksp = [Pb2+][F-]2

Ksp = (1.90 x 10-3)(3.80 x 10-3)2

Ksp = 2.74 x 10-8

PbF2(s) Pb2+(aq) + 2 F¯(aq)

[E] 0 1.9 x 10-3 M

[I] 1.9 x 10-3 M 0 0

[C] - x + x + 2x

3.8 x 10-3 MSaturated – all solid reactant dissociates.

Calculate Ksp if 50.0 mL of a saturated solution was found to contain 0.2207 g of lead (II) chloride.

I 0.0159 M 0 0C -x +x +2xE 0 0.0159 M 0.0318 M

Ksp = [Pb2+][Cl-]2

0.2207 g278.1g1 mol = 0.0159 M PbCl20.05 L

PbCl2(s) Pb2+(aq) + 2 Cl-

(aq)

Ksp = [0.0159][0.0318]2 = 1.61 x 10-5

Ksp of magnesium hydroxide is 8.9 x 10-12. What are the [equilibrium] of ions in saturated solution?

I --- 0 0C -x +x +2xE 0 x 2x

Mg(OH)2 (s) Mg2+(aq)

+ 2 OH-(aq)

Ksp = [Mg2+][OH-]2

8.9 x 10-12 = [x][2x]2

8.9 x 10-12 = [x]4x2

8.9 x 10-12 = 4x3

[Mg2+] = x = 1.3 x 10-4 mol/L

[OH-] = 2x = 2.6 x 10-4 mol/L

8.9 x 10-12 = 4x3

44

2.23 x 10-12 = x33√ 3√

1.3 x 10-4 = x

Precipitation

Compare value of Q, with given Ksp to determine if an aqueous solution is saturated or unsaturated.

Q = Ksp Saturated solution, no precipitate.

Q >Ksp Precipitate forms (“oversaturated”)

Q < Ksp Solution is unsaturated.

Qsp = [A+]a[B¯]b

· Substances which are insoluble are actually slightly soluble.

· The solubility product, Ksp, describes the product of ion concentrations in saturated solutions.

· Solubility can be determined from the solubility product.

CAN YOU / HAVE YOU?

• Write solubility product (Ksp) expressions from balanced chemical equations for salts with low solubility.

 • Solve problems involving Ksp.

Additional KEY TermsDissociation Saturated