1. The Solubility Product Constant (Ksp)

2. The Solubility Product Constant
Remember  not all salts are soluble!
AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
Write a net ionic equation for the above reaction:
Write Keq for the above equation
What would the dissolving of AgCl(s) look like in an equation?
Wait… is this Keq correct? Are solids included in a Keq equation?

3. The Solubility Product Constant
Since some AgCl remains an undissolved solid, the [AgCl] is constant:
Keq [AgCl] = [Ag+]x[Cl-] = Ksp
Ksp = solubility product constant
Measured at 25ºC
Ksp for AgCl = 1.8x10-10
Equilibrium occurs only at and past saturation point…so only if there is a undissolved alt mixed with dissolved salt

4. Write Ksp for each salt:
Practice Problems
Write Ksp for each salt:
PbCl2 and Ag2CrO4

5. Practice Problems
What is the Ag+ concentration in a saturated AgCl solution at 25ºC?
ICE chart can be included but usually not necessary since initial concentration of the ions are considered 0. The salt dissolves and produces x amount of ions…0 plus x equals x.
(Ksp for AgCl = 1.8x10-10)

6. Practice Problems
Calcium fluoride has a Ksp of 3.9x10-11 at 25ºC. What is the fluoride ion concentration at equilibrium?

7. Consider the following equation: PbCrO4 Pb+2 + CrO42- Ksp = 1.8x10-14
The Common Ion Effect
Consider the following equation:
PbCrO Pb+2 + CrO42-
Ksp = 1.8x10-14
What happens if we add lead (II) nitrate (Pb(NO3)2)?
What are we really adding?
Think about Le Châtelier's Principle!

8. The Common Ion Effect PbCrO4 Pb2+ + CrO42- PbCrO4 Pb2+ + CrO42-
The Pb2+ will precipitated until the product of Pb2+ and CrO42- is 1.8x10-14
Extra Pb2+ Added
The Ksp (just like the Keq) does not change when you add a reactant or product, the reaction shifts to accommodate this addition.

9. Common Ion: an ion added that is common to both salts
The Common Ion Effect
Common Ion: an ion added that is common to both salts
Pb2+ was common to PbCrO4 and Pb(NO3)2
Adding a common ion causes solubility to decrease
Called the common ion effect

10. Common Ion Problems
The Ksp of AgI is 8.3x What is the iodide-ion concentration of a 1.00-L saturated solution of AgI to which mol AgNO3 is added?\
With a common ion, an ICE chart could be useful.
What do you know?
Ksp = 8.3x10-17
Mol AgNO3 added = 0.020
AgI  Ag+ + I-
Ksp = [Ag+] x [I-]
What do you want to know?
[I-] = ?M
At equilibrium, [Ag+] = M
Plug that into Ksp to solve for [I-]
8.3x10-17 = (0.020 M)(x)
x = 4.2x10-15
Does this make sense?
Yes! With [Ag+] being so large, the [I-] should be small!

11. Another problem…
Would precipitation occur when 500mL of a 0.02M solution of AgNO3 is mixed with 500mL of a 0.001M solution of NaCl?
(Ksp for AgCl = 1.8x10-10)

12. Before you go…
A student prepares a solution by combining 0.025mol calcium chloride and 0.015mol lead (II) nitrate and adding water to make 1.0L of solution. Will a precipitate of lead (II) chloride form in this solution.
Ksp = 1.7x10-5