1. Solubility
Lesson 4
Calculating
Ksp

2. Refer to your Ksp table on page 333 of your textbook.
Ksp (the solubility product constant) is the product of the ion concentrations in a saturated solution raised to the power of their coefficients in the equilibrium.
Ksp is indeed a constant.
Only temperature changes can change the value of Ksp.
The higher the value of Ksp, the higher the solubility.
We can find the solubility product constant (Ksp) for certain compounds at 25 ºC
Refer to your Ksp table on page 333 of your textbook.
Provided for you.

3. 1. The solubility of BaCO3 is 5. 1 x 10-5 M @ 250 C. Calculate the
1. The solubility of BaCO3 is 5.1 x C. Calculate the solubility product or Ksp.
BaCO3(s) ⇌ Ba CO32-
Ba2+
CO32-
BaCO3(s)
x x x
Ksp = [Ba2+][CO32-]
Ksp = [x][x]
Ksp = x2
Ksp = (5.1 x 10-5)2
Ksp = x 10-9

4. Ksp
Solubility Product
Saturated solutions- at equilibrium
No Units
Increasing Temperature (for endothermic reactions) increases the solubility and therefore, increases the Ksp

5. Only 2 types of questions
Calculate the solubility product, Ksp.
Calculate the concentration of the ion/solubility, calculate he mass (that is, how many grams?) etc…

6. 2. The solubility of PbBr2 is 0.012 M @ 25 0C. Calculate the Ksp.
dissociation equation
PbBr2(s) ⇌ Pb Br-
solubility
x x 2x
equilibrium expression
Ksp = [Pb2+][Br-]2
substitute & solve
Ksp = [x][2x]2
Ksp = 4x3
Ksp = 4(0.012)3
Ksp = 6.9 x 10-6
Note that the Br- is doubled and then squared!

7. 3. If 0. 00243 g of Fe2(CO3)3 is required to saturate 100
3. If g of Fe2(CO3)3 is required to saturate mL of solution. What is the solubility product?
Fe2(CO3)3 ⇌ 2Fe CO32-
x x x
Ksp = [Fe3+]2[CO32-]3
Molarity = g
x 1 mole
291.6 g
Ksp = [2x]2[3x]3
0.100 L
Ksp = 108x5
= x 10-5 M
Ksp = 108(8.333 x 10-5)5
Ksp = x

8. TRY
If g of Fe(OH)3 is required to saturate mL of solution. What is the solubility product?

9. What if you are asked to find ion concentrations/solubility or mass?

10. Calculate the molar solubility of iron(II) hydroxide from its Ksp.
Write dissociation equation Find corresponding Ksp expression

11. TRY: what mass is dissolved in 275 mL of saturated silver bromate?

12. Last few tips
Don’t ever start a question without writing the dissociation equation first.
Don’t forget to BALANCE this equation.
Don’t forget to use your coefficients as powers in Ksp equation
Use molar mass when converting from gramsmoles or moles grams.

13. Homework: Try ALL of these questions
Homework: Try ALL of these questions! Hebden: Pg 95 #43, 44, 46, 47, 49, 50, 52, 55