Last Class
• 18.4 Solubility of Salts. Ksp
Ksp Expressions
AgI
BaF2
Ag2CO3
Solubility of Lead(II) Chloride
Today
PbCl2(s) ' Pb2+(aq
aq)) + 2 Cl-(aq
aq))
Ksp = 1.9 x 10-5 = [Pb2+][
][Cl
Cl–]2
• 18.4 Solubility of Salts: S
1
Ksp: Quantifies Solubility
Ksp from Solubility
Calculate the Ksp value for CaF2 if the calcium ion
concentration in a saturated solution
has been found to be 2.4 x 10-4 M.
AgCl (s) ' Ag+(aq)
aq) + Cl-(aq)
aq)
Ksp = [Ag+]eq[Cl–]eq = 1.9 x 10-10
Qsp < Ksp Æ soluble, no precipitation
sobresaturated))
Qsp > Ksp Æ exceeds solubility, precipitation ((sobresaturated
Qsp = Ksp Æ at equilibrium, saturated solution
Solubility of Lead(II) Iodide
Pbl2(s
(s)) ' Pb2+(aq
aq)) + 2 l-(aq
aq))
Ksp = 9.8 x 10-9 = [Pb2+]eq[l–]eq2
Solubility from Ksp
Pbl2(s) ' Pb2+(aq
aq)) + 2 l-(aq
aq))
The value of Ksp
depends on a
‘competition’
between interactions
in the solid and ion
solvation.
The equilibrium
dissociated ions in
solution and the
precipitate is
dynamic.
At equilibrium:
the rate of
dissolution = the
rate of precipitate
formation
Lead Iodide
As the interactions
in the solid become
more favorable
(and/or ion solvation
becomes poorer),
the substance
becomes more
insoluble. (Ksp
becomes smaller.)
2
Solubility Expressions
The Solubility of CoCO3 in the following solutions is:
1) the same,
2) higher
higher, or
3) lower
than in water?
a- NH4AcO
b NaNO3
bc- Na2CO3
d- Co(AcO)2
3