16.6 Solubility Equilibria: 16.6 Solubility Equilibria


Solubility Equilbria: Solubility Equilbria Many ionic cmpds are very soluble in water (as NaCl) but others have limited solubility--p 109 table 4.2


Slide3: Let’s envision what happens when make a saturated solution of some ionic cmpd of limited solubility, as CaCO3. Assume that the solvent is water and the temp is 25oC. CaCO3(s)  Ca2+(aq) + CO32-(aq)    CaCO3(aq) A certain quantity of CaCO3 goes into solution and immediately dissociates into ions. _______________


Slide4: A saturated solution has ___________ Remember in writing equil expressions that pure solids, pure liquids--______.


Solubility Product: Solubility Product CaCO3(s)  Ca2+(aq) + CO32-(aq) Ksp = _____________ Ksp is called the _______________ (equil constant) (Implies ideal behavior) [Ca2+] implies conc units in _________ Ksp values tabulated in book, p 672, table 16.2


Relationship btn molar sol’y (s) and Ksp: Relationship btn molar sol’y (s) and Ksp Define molar solubility, s ,as the ________ Let us examine the stoichiometrically different salts and their relationship to molar solubility.


Slide7: 1:1 salt as AgCl, CaCO3 AgCl(s)  Ag+(aq) + Cl-(aq) Ksp = ____________ [Ag+] = [Cl-] = ____


Slide8: 2:1 or 1:2 salt as CaF2 or Ag2SO4 CaF2(s)  Ksp = ________ [F-] = __ [Ca2+] = __


Slide9: 1:3 or 3:1 salt as Fe(OH)3 or Ag3PO4 Ag3PO4(s)  Ksp = [Ag+] = ___ [PO43-]= ___


Slide10: 2:3 or 3:2 salt as Bi2S3 or Ca3(PO4)2 Bi2S3(s)  Ksp = [Bi3+] = ___ [S2-] = _____ Remember this assumes ideal behavior (as complete ionization--no ion pair formation, no hydrolysis of ions as Al3+ )


Ksp and Q (ion-product): Ksp and Q (ion-product) Remember Ksp refers to a saturated sol’d, Q refers to any sol’n, not just an equilibrium system. Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = [Ag+]3[PO43-] Q = [Ag+]3[PO43-] : these need not be equil concs


Slide12: If Q Ksp _______


Problems: Ksp to s and s to Ksp : Problems: Ksp to s and s to Ksp What are the molar solubilities of CaCO3(Ksp = 8.7 x 10-9) and Ag2CO3 (Ksp = 8.1 x 10-12) Calc Ksp of Ag3PO4, given the sol’y of Ag3PO4 is 6.7 x 10-3 g/L


Slide14: 16.45: The sol’y of an ionic cmpd, M2X3 (molar mass=288g) , is 3.6 x 10-17 g/L. What’s the Ksp? 16.47:What is the pH of a saturated zinc hydroxide sol’n? 16.48: The pH of a sat’d sol’n of a metal hydroxide, MOH, is 9.68. Calc. the Ksp.


Mix two sol’s together, do you get a ppt (predicting ppt rxns): Mix two sol’s together, do you get a ppt (predicting ppt rxns) Do you get a ppt if mix 10 mL of 0.0010M AgNO3 and 10 ml of 0.0010M Na2SO4 10 mL of 1.0 x 10-6M iron(II) chloride and 20 ml of 3.0 x 10-4M barium hydroxide


Slide16: 16.50: A volume of 75 mL of 0.060 M NaF is mixed with 25 mL of 0.15 M Sr(NO3)2. Calc the concs in the final soln of NO3-, Na+, Sr2+, and F-. Ksp for SrF2 is 2.0 x 10-10.


16.8: The common ion effect and solubility: 16.8: The common ion effect and solubility What does Le Chatelier say about the presence of a common ion and solubility AgI(s)  Ag+(aq) + I-(aq)  add Ag+ from AgNO3 ___________


Slide18: Calculate the molar sol’y of SrF2 (Ksp = 2.0 x 10-10) in water in 0.010 M Sr(NO3)2 in 0.010 M NaF _________ 16.56 similar


Slide19: 16.55: How many grams of CaCO3 will dissolve in 300 mL of 0.050 M Ca(NO3)2?


Slide20: What’s the solubility of Fe(OH)3 in HOH? Ksp for Fe(OH)3 =1.1 x 10-36. So does changing pH affect solubility of insoluble hydroxides? 16.62: Calc the pH of Fe(OH)2 in water and at a pH of 7.00, at a pH of 8.00 and at a pH of 10.00. 16.61: Compare the molar soly of Mg(OH)2 in water and in a soln buffered at a pH of 9.00 .


Factors that affect solubility: Factors that affect solubility 1. _______ 2. common ion ____________ 3. pH: salt contains anion (conj base of WA): ____________ CaF2(s)  Ca2+(aq) + 2F-(aq)  H+


Slide22: 4. hydroxides--pH: ___ Except for amphoteric hydroxides as Al(OH)3, Pb(OH)2, Cr(OH)3, Zn(OH)2, Cd(OH)2 Al(OH)3 + OH-  Al(OH)4-(aq) As pH increases (add more OH-), tie up the hydroxide salt as a soluble complex,


Slide23: 5.Complex ion formation Cu2+(aq) +2OH- Cu(OH)2(s) Cu(OH)2(s) + 4NH3(aq)  Cu(NH3)42+(aq) complex ion Cu2+(aq) + 4NH3(aq) Cu(NH3)42+(aq) Kf = [Cu(NH3)42+] = 5.0 x 1013 [Cu][NH3]4 Table of formation constants Kf, p 685, table 16.4


Slide24: 16.67: If 2.50 g of CuSO4 are dissolved in 900 mL of 0.30 M NH3, what sre the concs of Cu2+, Cu(NH3)42+ and NH3 at equilibrium? 16.70: Calc the molar soly of AgI in a 1.0 M NH3 soln.


Slide25: Which of the following will be more soluble in acid solution than in water? BaSO4 PbCl2 Fe(OH)3 CaCO3 Ca3(PO4)2 AgBr


Slide26: 16.54: The molar soly of AgCl in 6.5x10-3M AgNO3 is 2.5 x 10-8 M. In deriving Ksp from these data which of the following assumptions are reasonable? Ksp is the same as soly. Ksp of AgCl is the same in 6.5x10-3M AgNO3 as in pure water. Soly of AgCl is independent of the conc of AgNO3.


Slide27: [Ag+] in soln does not change significantly upon the addition of AgCl to 6.5x10-3M AgNO3. [Ag+] in soln after the addition of AgCl to 6.5x10-3M AgNO3 is the same as it would be in pure water.