View
218
Download
1
Category
Tags:
Preview:
Citation preview
Previously in Chem104:
•Titration review
•Buffers: little more
• Lewis acid/base reactions
• complex ions• solubility
• Solubility Product
Today in Chem104:
• Solubility Product• Ksp• Common Ion Effect• pH effect• Chelate Effect
• Examples
• Iron Bioavailability:•an example of asolubility problem for Life
All ionic solids dissolve using Lewis A/B interactions
MX(s) + 6H2O [M(H2O)6]+ + X(aq)-
M+:OH2
e- acceptor :e- donorLewis Acid :Lewis Base
Mn+
H2O
H2O OH2
OH2
H2O
OH2
All ionic solids dissolve using Lewis A/B interactions
AgCl(s) + 2H2O [Ag(H2O)2]+ + Cl-
Ksp = 1.8 x10-10 Ksp = [Ag+][Cl-] and [Ag+] = [Cl-] 1.8 x10-10 = [Ag+][Cl-] = x2
AgCl(s) Ag+ + Cl-Written simply:
This is typical expression for solubility equilibriumGiven by the Solubility Product Ksp
Very low solubility due to weak Lewis A/B interactions which does not compensate for large lattice energy
x = 1.3 x10-5 M = [Ag+] = [Cl-] This is the molar solubility of AgCl
Ionic solids which completely dissolve are highly soluble and cannot be described with a Ksp
NaCl(s) + 6H2O [Na(H2O)6]+ + Cl-
Ionic solids which slightly dissolve are thosewhose solubility can be described with a Ksp
AgCl(s) Ag+ + Cl- Ksp = 1.8 x10-10
CaCO3(s) Ca2+ + CO32- Ksp = 3.4 x10-9
CaF2(s) Ca2+ + 2 F- Ksp = 5.3 x10-11
Ag2S(s) 2 Ag+ + S2- Ksp = 6.1 x10-51
Solubility obeys
AgCl(s) Ag+ + Cl- + excess Cl-
Ksp = 1.8 x10-10 Solubility =1.3 x10-5 M = [Ag+] = [Cl-]
AgCl(s) Ag+ + Cl-
If more chloride is added the equilbirum shifts left,and Solubility Product Ksp requires less AgCl dissolves
Ksp = 1.8 x10-10 Solubility, [Ag+] <1.3 x10-5 M
What if more Cl- is added to this equilibrium?
otherwise called The Common Ion Effect obeys
AgCl(s) Ag+ + Cl- + excess Cl-
Ksp = 1.8 x10-10 and Solubility =1.3 x10-5 M = [Ag+] = [Cl-]
For the dissolution of silver chloride, AgCl(s) Ag+ + Cl-
When additional chloride is added, Solubility Product Ksp requires less AgCl dissolves
Ksp = 1.8 x10-10 but
Solubility of silver ion is decreased, [Ag+] <1.3 x10-5 M because [Cl- ] >>1.3 x10-5 M
The pH Effect obeys
Ksp = 3.7 x10-9
Ca(CO3)(s) Ca2+ + CO32-
If pH is lowered by adding acetic acid,more CaCO3 dissolves
…. and cleans the teapot:
+ AH
HCO3-
H2CO3
+ AHH2O + CO2
+ AH
The Chelate Effect obeys
Ksp = 3.7 x10-9
Ca(CO3)(s) Ca2+ + CO32-
If Ca2+ is removed by adding a ligand,
more CaCO3 dissolves
…. and also cleans the dishwasher:
+ citric acid
Ca(citrate)
COOHHOC
COOHHOO
-OCCO-
-OC
OH
O
O
OCa2+
Making better (stronger) Lewis A/B interactionscan improve solubility and clean, too
We have seen:AgCl(s) + 2H2O [Ag(H2O)2]+ + Cl-
Ksp = 1.8 x10-10
AgCl can be completely dissolved!
Very low solubility due to weak Lewis A/B interactions which do not compensate for large lattice energy
But if ammonia is Lewis base:AgCl(s) + 2 NH3 [Ag(NH3)2]+ + Cl-
Does Q have a role in Ksp problems? YES!!Possible outcomes for MX(s) <==> M+ + X-
1. Q Ksp
2. Q < Ksp
3. Q > Ksp
Reactants Products; all salt dissolved
Reactants & Products in equilibrium; Solution is Saturated
Products Reactants; solid precipitates
Recommended