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

Cleanliness is

next to Godliness

So controlling solubility can make you more holy?

Let’s see how…

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

A Siderophore“iron carrier”

Iron(III) Siderophoreready for transport