SolubilityLesson 4

CalculatingKsp

Ksp

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 ºCRefer to your Ksp table on page 333 of your textbook.

Provided for you.

1. The solubility of BaCO3 is 5.1 x 10-5 M @ 250 C. Calculate the

solubility product or Ksp.

Ba2+ CO32-

BaCO3(s)

BaCO3(s) ⇌ Ba2+ + CO32-

x x x

Ksp = [Ba2+][CO32-]

Ksp = [x][x]

Ksp = x2

Ksp = (5.1 x 10-5)2

Ksp = 2.6 x 10-9

Increasing Temperature (for endothermic reactions) increases the solubility and therefore, increases the Ksp

No Units

Saturated solutions- at equilibrium

Solubility Product

Ksp

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…

2. The solubility of PbBr2 is 0.012 M @ 25 0C. Calculate the Ksp.

Note that the Br- is doubled and then squared!

Ksp = 6.9 x 10-6

Ksp = 4(0.012)3

Ksp = 4x3

Ksp = [x][2x]2

Ksp = [Pb2+][Br-]2

x x 2x

PbBr2(s) ⇌ Pb2+ + 2Br-dissociation equation

solubility

equilibrium expression

substitute & solve

3. If 0.00243 g of Fe2(CO3)3 is required to saturate 100.0 mL of solution.

What is the solubility product?

Ksp = 4.34 x 10-19

Ksp = 108(8.333 x 10-5)5

Ksp = 108x5

Ksp = [2x]2[3x]3

Ksp = [Fe3+]2[CO32-]3

= 8.333 x 10-5 M

0.100 L

291.6 g

x 1 mole0.00243 gMolarity =

x 2x 3x

Fe2(CO3)3 ⇌ 2Fe3+ + 3CO32-

TRYIf 0.0047 g of Fe(OH)3 is required to saturate 200.0 mL of solution.

What is the solubility product?

What if you are asked to find ion concentrations/solubility or

mass?

Calculate the molar solubility of iron(II) hydroxide from its Ksp.

Write dissociation equation

Find corresponding Ksp expression

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

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

gramsmoles or moles grams.

Homework: Try ALL of these questions!

Hebden: Pg 95

#43, 44, 46, 47, 49, 50, 52, 55