Solubility

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
Determining The Solubility of MgCl2
Add measured portions of MgCl2 to 100.0 mL and
stir to dissolve
Amount MgCl2 Dissolved
Rate of dissolving gt Rate of crystallization
10.0 g
MgCl2
MgCl2
MgCl2
MgCl2
MgCl2
10.0 g
unsaturated
10.0 g
slow
100.0 mL
3.0 g
very slow
0.0 g
saturated
33.0 g
equilibrium
Rate of dissolving Rate of crystallization
MgCl2(s)
4
Calculate the solubility in units of g/L and
mole/L
33.0 g
Solubility
330. g/L
0.100 L
the molarity to saturate
molar solubility
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) ? Mg2 2Cl-
Expression
Keq Mg2Cl-2
Ksp Mg2Cl-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 gt 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 lt the rate of
crystallizing
Not at equilibrium
10
What we just calculated was exact solubility
The data book page 4 gives us relative solubility
High Solubility means gt .1 M
Low Solubility means ? .1M
CuCl2
Na3PO4
High
High
CuCl
Ca(NO3)2
Low
High
High
K2CO3  
CuSO4
High
Ag2SO4
CaSO4
Low
Low
BaS
FeSO4
High
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) ? C6H12
O6(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 Al32SO42-3
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 Ca23PO43-2
Supersaturated video