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Previously in Chem104: Titration review Buffers: little more Lewis acid/base reactions

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

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Previously in Chem104: Titration review Buffers: little more Lewis acid/base reactions

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  1. 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

  2. All ionic solids dissolve using Lewis A/B interactions MX(s) + 6H2O [M(H2O)6]+ + X(aq)- M+:OH2 e- acceptor :e- donor Lewis Acid :Lewis Base

  3. All ionic solids dissolve using Lewis A/B interactions AgCl(s) + 2H2O [Ag(H2O)2]+ + Cl- Very low solubility due to weak Lewis A/B interactions which does not compensate for large lattice energy Written simply: This is typical expression for solubility equilibrium Given by the Solubility Product Ksp AgCl(s) Ag++ Cl- Ksp = 1.8 x10-10 Ksp = [Ag+][Cl-] and [Ag+] = [Cl-] 1.8 x10-10 = [Ag+][Cl-] = x2 x = 1.3 x10-5 M = [Ag+] = [Cl-] This is the molar solubility of AgCl

  4. 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 those whose solubility can be described with a Ksp AgCl(s) Ag+ + Cl- Ksp = 1.8 x10-10 Ag2S(s) 2 Ag+ + S2- Ksp = 6.1 x10-51 CaCO3(s) Ca2+ + CO32- Ksp = 3.4 x10-9 CaF2(s) Ca2+ + 2 F- Ksp = 5.3 x10-11

  5. Solubility obeys Le Chatelier’s Principle AgCl(s) Ag++ Cl- Ksp = 1.8 x10-10 Solubility =1.3 x10-5 M = [Ag+] = [Cl-] If more chloride is added the equilbirum shifts left, and Solubility Product Ksp requires less AgCl dissolves What if more Cl- is added to this equilibrium? AgCl(s) Ag+ + Cl- + excess Cl- Ksp = 1.8 x10-10 Solubility, [Ag+] <1.3 x10-5 M

  6. otherwise called The Common Ion Effect obeys Le Chatelier’s Principle For the dissolution of silver chloride, AgCl(s) Ag++ Cl- Ksp = 1.8 x10-10 and Solubility =1.3 x10-5 M = [Ag+] = [Cl-] When additional chloride is added, Solubility Product Ksp requires less AgCl dissolves AgCl(s) Ag+ + Cl- + excess Cl- Ksp = 1.8 x10-10but Solubility of silver ion is decreased, [Ag+] <1.3 x10-5 M because [Cl- ] >>1.3 x10-5 M

  7. Cleanliness is next to Godliness So controlling solubility can make you more holy? Let’s see how…

  8. The pH Effect obeys Le Chatelier’s Principle …. and cleans the teapot: Ca(CO3)(s) Ca2+ + CO32- Ksp = 3.7 x10-9 + AH HCO3- H2O + CO2 If pH is lowered by adding acetic acid, more CaCO3 dissolves + AH + AH H2CO3

  9. The Chelate Effect obeys Le Chatelier’s Principle …. and also cleans the dishwasher: Ca(CO3)(s) Ca2+ + CO32- Ksp = 3.7 x10-9 + citric acid Ca(citrate) If Ca2+ is removed by adding a ligand, more CaCO3 dissolves

  10. Making better (stronger) Lewis A/B interactions can improve solubility and clean, too We have seen: AgCl(s) + 2H2O [Ag(H2O)2]+ + Cl- Very low solubility due to weak Lewis A/B interactions which do not compensate for large lattice energy Ksp = 1.8 x10-10 But if ammonia is Lewis base: AgCl(s) + 2 NH3 [Ag(NH3)2]+ + Cl- AgCl can be completely dissolved!

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

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

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