1. KSP = Solubility product constant

2. Ksp: The Solubility-Product Constant
Ksp is the solubility product constant
It is like Keq for dissociation reactions

3. Ksp: The Solubility-Product Constant
It has to do with solid substances usually considered insoluble in water.
Note that these are the ones we usually say have ‘low solubility’
In each example, we will consider a saturated solution of the insoluble substance. Some points to consider are:
1) Some of the solid does dissolve. Not very much, but enough.
2) The substance dissociates upon dissolving.
3) There exists an equilibrium between the undissolved solid and the solvated ions.

4. Setting up Ksp Expressions
Since equilibrium principles can be used, that is where we start. Our first example is silver chloride, AgCl. When it dissolves, it dissociates like this:
AgCl (s)   Ag+ (aq) + Cl- (aq)
**ALWAYS WRITE THE SOLID AS A REACTANT**
An equilibrium expression can be written:
Keq = [Ag+] [Cl-]
[AgCl]

5. Setting up Ksp Expressions
Remember that in an equilibrium expression, we DO NOT WRITE SOLIDS OR LIQUIDS
In a Ksp expression, there will be no solid.
In other words, there is no reactant in our expression
For our previous example:
AgCl(s) ⇌ Ag+(aq) + Cl-(aq)
Since we don’t include a solid, Ksp will look like:
𝐾𝑠𝑝= 𝐴𝑔 + [ 𝐶𝑙 − ]

6. Writing Ksp Expressions
EACH CONCENTRATION IN THE Ksp EXPRESSION IS RAISED TO THE POWER OF ITS COEFFICIENT IN THE BALANCED EQUATION.
In order to write Ksp expressions properly, you must know how ionic substances dissociate in water. That means, you have to know your chemical nomenclature, polyatomic ions, and the charges associated with ion.

7. Writing Ksp Expressions - Examples
Sn(OH)2 (s) ↔ Sn2+ (aq) + 2 OH¯ (aq)
Ksp = [Sn2+] [OH¯]2
Ag2CrO4 (s) ↔ 2 Ag+ (aq) + CrO42¯ (aq)
Ksp = [Ag+]2 [CrO42¯]
Fe(OH)3 (s) ↔ Fe3+ (aq) + 3 OH¯ (aq)
Ksp = [Fe3+] [OH¯]3

8. Calculations Using Ksp
1) Calculating the Ksp
The concentration of lead ions in a saturated solution of PbI2 at 25˚C is 1.3 x 10-3 M. What is the solubility product constant?

9. Calculations Using Ksp
2) Calculating Concentrations
A) In a 1:1 Ratio
The Ksp for MgCO3 at 25˚C is 2.0 x What are the ion concentrations in a saturated solution at this temperature?

10. Calculations Using Ksp
2) Calculating Concentrations
B) NOT in a 1:1 ratio
Calculate the molar concentration for silver chromate in a saturated solution at 25˚C. Ksp = 1.1 x 10-12