1. Solubility
Unit III
Lesson 1

2. Solubility is the maximum amount of solute that will dissolve in a volume of water.
Units:
g/L
mol/L
g/100 mL
The unit must have an amount on the top and volume on the bottom!
In order to determine the solubility you must completely fill or saturate the solution!
To saturate a solution, add weighed portions of the solid to a volume of water and stir until full.
A bit of excess solid is present when saturated.

3. unsaturated saturated MgCl2(s) Determining The Solubility of MgCl2
Add measured portions of MgCl2 to mL and stir to dissolve
Amount MgCl2 Dissolved
Rate of dissolving > Rate of crystallization
10.0 g
MgCl2
MgCl2
MgCl2
MgCl2
MgCl2
unsaturated
10.0 g
10.0 g
slow
100.0 mL
3.0 g
very slow
0.0 g
Mg2+
Cl-
saturated
33.0 g
equilibrium
MgCl2(s)
Rate of dissolving = Rate of crystallization

4. Calculate the solubility in units of g/L and mole/L
molar solubility =
the molarity to saturate
33.0 g
x 1 mole
95.3g
s =
0.100 L
= 3.46 M

5. do not use the solid
Equilibrium Equation
MgCl2(s) ⇌ Mg Cl-
Expression:
Keq = [Mg2+][Cl-]2
Ksp = [Mg2+][Cl-]2
The Ksp or solubility product is used for saturated solutions at equilibrium

6. This unit is all about the Ksp and the solubility of saturated solutions.

7. Unsaturated Solutions
Not full -more solid dissolves
The rate of dissolving > the rate of crystallizing
Not at equilibrium

8. Saturated Solutions
Full-more solid does not dissolve
The rate of dissolving = the rate of crystallizing
At equilibrium

9. Supersaturated Solutions
Over full -more solid causes precipitation
The rate of dissolving < the rate of crystallizing
Not at equilibrium

10. What we just calculated was exact solubility
The data book page 4 gives us relative solubility
Low Solubility means  .1M
High Solubility means > .1 M
Na3PO4
High
CuCl2
High
Ca(NO3)2
High
CuCl
Low
K2CO3  
High
High
CuSO4
CaSO4
Low
Ag2SO4
Low
FeSO4
High
BaS
High

11. Ionic Solutions Molecular Solutions
NaCl(aq) C6H12O6(aq) metal
Ca(OH)2(aq) C12H22O11(aq) nonmetal
(NH4)3PO4(aq) CH3OH(aq)
Ca(CH3COO)2(aq) O2(aq)
H2SO4(aq) N2H4(aq)
Conduct electricity Do not conduct electricity

12. Write dissociation (ionic) or dissolving (molecular) equations for the first six compounds to show how each dissolves in water.
The first five are solids and the sixth one is a liquid.
NaCl(s)  Na+ + Cl-
C6H12O6(s)  C6H12O6(aq)
Ca(OH)2(s)  Ca2+ + 2OH-
C12H22O11(s)  C12H22O11(aq)
(NH4)3PO4(s)  3NH4+ + PO43-
CH3OH(l)  CH3OH(aq)

13. Write the equation for equilibrium present in a saturated solution of Al2(SO4)3(s) solution.
Al2(SO4)3(s) ⇌ 2Al3+ + 3SO42-
Equilibrium Expression
Ksp = [Al3+]2[SO42-]3

14. Write the equation for equilibrium present in a saturated solution of Ca3(PO4)2(s) solution.
Ca3(PO4)2(s) ⇌ 3Ca2+ + 2PO43-
Equilibrium Expression
Ksp = [Ca2+]3[PO43-]2
Supersaturated video