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 a solubility problem for Life

All ionic solids dissolve using Lewis A/B interactions MX(s) + 6H 2 O[M(H 2 O) 6 ] + + X(aq)- M +  :OH 2 e- acceptor  :e- donor Lewis Acid  :Lewis Base

All ionic solids dissolve using Lewis A/B interactions AgCl(s) + 2H 2 O[Ag(H 2 O) 2 ] + + Cl- K sp = 1.8 x K sp = [Ag+][Cl-] and [Ag+] = [Cl-] 1.8 x = [Ag+][Cl-] = x 2 AgCl(s)Ag+ + Cl- Written simply: This is typical expression for solubility equilibrium Given by the Solubility Product K sp 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 K sp NaCl(s) + 6H 2 O[Na(H 2 O) 6 ] + + Cl- Ionic solids which slightly dissolve are those whose solubility can be described with a K sp AgCl(s)Ag + + Cl- K sp = 1.8 x CaCO 3 (s)Ca 2+ + CO 3 2- K sp = 3.4 x10 -9 CaF 2 (s)Ca F - K sp = 5.3 x Ag 2 S(s)2 Ag + + S 2- K sp = 6.1 x10 -51

Solubility obeys AgCl(s)Ag + + Cl- + excess Cl- K sp = 1.8 x Solubility =1.3 x10 -5 M = [Ag+] = [Cl-] AgCl(s)Ag+ + Cl- If more chloride is added the equilbirum shifts left, and Solubility Product K sp requires less AgCl dissolves K sp = 1.8 x 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- K sp = 1.8 x 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 K sp requires less AgCl dissolves K sp = 1.8 x 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 K sp = 3.7 x10 -9 Ca(CO 3 )(s)Ca 2+ + CO 3 2- If pH is lowered by adding acetic acid, more CaCO 3 dissolves …. and cleans the teapot: + AH HCO 3 - H 2 CO 3 + AH H 2 O + CO 2 + AH

The Chelate Effect obeys K sp = 3.7 x10 -9 Ca(CO 3 )(s)Ca 2+ + CO 3 2- If Ca2+ is removed by adding a ligand, more CaCO 3 dissolves …. and also cleans the dishwasher: + citric acid Ca(citrate)

Making better (stronger) Lewis A/B interactions can improve solubility and clean, too We have seen: AgCl(s) + 2H 2 O [Ag(H 2 O) 2 ] + + Cl- K sp = 1.8 x 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 NH 3 [Ag(NH 3 ) 2 ] + + Cl-

Does Q have a role in K sp problems? YES!! Possible outcomes for MX(s) M + + X - 1. QK sp 2. Q <K sp 3. Q >K sp Reactants  Products; all salt dissolved Reactants & Products in equilibrium; Solution is Saturated Products  Reactants; solid precipitates

A Siderophore “iron carrier” Iron(III) Siderophore ready for transport