1. Lesson 6: The Solubility Product
Unit 3: Solubility
Lesson 6: The Solubility Product

2. The Solubility Product
For a solubility equilibrium, Keq is given a special name – the solubility product constant (Ksp).
The equilibrium expression is called the solubility product expression.
E.g. For CaF2(s) Ca2+(aq) + 2 F-(aq), Ksp = [Ca2+][F-]2

3. Important!
In a saturated solution, the solubility product is the ion concentrations multiplied together, while the solubility of a substance is the concentration of that substance.

4. The Meaning of Ksp
Since the value of Ksp depends on the concentrations of the ions, a larger value of Ksp indicates a more soluble salt, and vice versa.
Try This: Which of the following salts is the most soluble? The least?
AgCl ; Ksp = 1.8x10-10
AgI ; Ksp = 8.5x10-17
AgBr ; Ksp = 5.4x10-13
5 min

5. Brain Break – Spot 6 Differences!

6. Preparing a Saturated Solution
Two possible methods:
Put a solid compound into water and let it dissolve. The ratio of the ions follows the stoichiometric ratio.
Separately add the ions of the compound into water. We do not know the ratio of the ions unless we are given the experimental values!
Use CaF2 as an example. – 5 min

7. Ksp Calculations
Example 1: A solution in equilibrium with a precipitate of BaF2 contains 4.59x10-2 M Ba2+ and 2.00x10-3 M F-. What is Ksp for BaF2?
Example 2: A saturated solution of BaF2 contains 3.58x10-3 mol of BaF2 in 1.00 L of solution. What is Ksp for BaF2?
Example 3: What is the [Mg2+] in a saturated solution of Mg(OH)2?
For #3, let x=[Mg(OH)2]dissolved then solve using Ksp. – 15 min

8. Practice
Pg. 91 #40
Pg. 95 #42-43, 46-47, and 54
5 min