1. Solubility Product Constant, Ksp

2. Solubility
is the maximum amount of solute in a solvent at a given temperature
saturated solution, [ ]max
equilibrium between:
solid crystals  dissolved ions
eg. AgNO3(s)  Ag1+(aq) NO31-(aq)

3. 1st 1st - H2O needs to separate - H-bonding needs to be overcome
- dissolving
- NRG input

4. 3rd 2nd 3rd 2nd - H2O removes ions from the lattice - dissociation
- NRG input
2nd
3rd - hydration of ions
- Ion – dipole force
3rd
- NRG output
-  with  H2O

5. • solubility is a contest between:
• ionic bond strengths vs ion-dipole forces
• lattice energies vs hydration energies
• usually exothermic with increased disorder
• if undissolved solid is present, then it is a mixture with a saturated sol’n phase

6. Solubility Product Constant, Ksp:
equilibrium expression for slightly soluble salts
If: AxBy(s)  xAm+(aq) yBn-(aq)
Then:

7. Saturation can be tested by Q:
If: Q = Ksp then it is a saturated solution
Q > Ksp there is noticeable precipitate
Q < Ksp unsaturated
Terminology:
refers to the amount of solid that can dissolve not how much is in solution
solubility units are g/100g or g/100 mL or g/L

8. To find molar solubility from solubility:
(concentration)
[ ]max = solubility ÷ Msolute x V adjustment
or 1/ Msolute
eg. Solubility of Mg(OH)2 is 3.45 g/100 mL.

9. To find solubility from molar solubility:
(concentration)
Solubility = molar solubility x Msolute x V adjustment
eg. Molar solubility of Mg(OH)2 is mol/L.
Do not divide by 100 mL

10. 1st - calculate the [ ] from solubility:
1) Ksp from solubility
eg. Calculate the Ksp of Ag2CO3 given its solubility of g/100g.
1st - calculate the [ ] from solubility:
2nd - create ICE table.
- Since dealing with a solid, the equilibrium is simplified

11. Ag2CO3 ↔ 2 Ag+ + CO32- ;
Q – not necessary
100 Rule
– not necessary

12. 2) Solubility from Ksp
types: solubility, molar solubility, [ion]eq, amount of solid that will dissolve
- all from calculating “x”
eg. How much PbI2 at SATP will dissolve in 1.00 L of water? Give the solute ion concentration, [Pb2+]eq, solubility (g/100mL) and molar solubility.
- when not given the Ksp and not asked to calculate it, find it in the reference table or the textbook
Ksp of PbI2 from textbook is 8.5 x 10-9

13. PbI2 ↔ Pb2+ + 2 I1- ; ICE +x +2x = the molar solubility
- as the solid is not included and the [ion]i = 0, we can write ICE horizontally instead of vertically
PbI2 ↔ Pb I1- ;
ICE
+x x
= the molar solubility

14. Predicting Precipitation:
Don’t  by it is a unit 100 mL
Predicting Precipitation:
• Used to determine precipitation when mixing 2 sol’ns just like in double displacement rxns

15. eg. Will precipitation occur when 5. 0 ml of 0
eg. Will precipitation occur when 5.0 ml of M AgNO3 is mixed with 1.0 ml of M Na2CrO4? (Ksp = 1.1 x for Ag2CrO4)?
1st – write down each reaction and calculate the V and C values

16. 3rd – calculate Q and compare with Ksp
2nd – write down the equilibrium equation, calculate the new [ ] in the combined sol’n
Ag2CrO4 ↔ 2 Ag CrO42- ;
3rd – calculate Q and compare with Ksp

17. eg. Will 0. 10 mg of Ba(OH)2 added to 75 mL of 2
eg. Will 0.10 mg of Ba(OH)2 added to 75 mL of 2.0 x 10-3 M AgNO3 solution form a precipitate? (Ksp (AgOH) = 1.5 x 10-17)?
Ba(OH)2  Ba OH-
= 1.17 x 10-6 mol
C = 2.0 x 10-3 M V = L

18. AgOH ↔ Ag+ + 2 OH- ; C = 2.0 x 10-3 M = 1.56 x 10-5 M
Ksp = [Ag+][OH-]
= 1.5 x 10-17
C = 2.0 x 10-3 M
= x 10-5 M
Q = (2.0 x 10-3)(1.56 x 10-5)
= 3.1 x 10-8 M
Q (3.1 x 10-8)
>
Ksp (1.5 x 10-17)