PP 25: Solubility Equilibria Drill: Determine the Q-/HQ ratio to make a buffer solution with a pH of 4.70: (Ka for HQ = 3.0 x 10-5) Solubility: The amount of one substance that will dissolve in another Saturated Solution: When the maximum amount of one substance is dissolved in another Precipitation: When dissolved particles come together, change phases & fall out of the solution. When more than the maximum amount of solute is added to a solution, a ppt will form Precipitate (ppt): The new phase that forms and leaves the solution • Water vapor combining to form rain • Dissolved ions combining to form a solid Solubility Equilibrium: Write the equilibrium expression for the following reaction: AgCl(s) Ag+ + Cl- Becaure the AgCl is a solid, not in phase with the solution, it counts as 1 in the Keq. Equilibrium Expression: Ksp = [Ag+][Cl-] MX(s) M+(aq) + X-(aq) Solubility Products: Rxn: Equilibrium Expression: Ksp = [M+][X-] MX2(s) M+(aq) + 2 X-(aq) Solubility Products: Rxn: Equilibrium Expression: Ksp = [M+][X-]2 Problem: Write the equation & equilibrium expression for: Al2(SO4)3 Al2(SO4) 3(s) 2 Al+3(aq) + 2 SO4-2(aq) Rxn: Equilibrium Expression: Ksp = [Al+3]2[ SO4-2]3 Drill: Write the reaction & equilibrium expression when solid Fe2(SO4)3 is added to water. Solubility Equilibria Calculations: Demonstrate: Calculate the solubility of BaSO4(s) 1. 2. 3. 4. 5. Set up & balance rxn: Assign Eq. amounts: Write the Keq: Substitute: Solve for x: (Ksp = 1.2 x 10-10) 1 BaSO4 1 Ba+2 + 1 SO4-2 1–x x x +2 -2 Ksp = [Ba ][ SO4 ] Ksp = [x][x] Ksp = [x]2 = Ksp = 1.2 x 10-10 x = solubility = 1.1 x 10-5 M Problems: Calculate the solubility of SrCr2O7(s) : Calculate the solubility of PbI2(s): Calculate the solubility of Mn2S3(s) (Ksp = 2.5 x 10-13) (Ksp = 8.0 x 10-9) (Ksp = 1 x 10-98) Common Ion Effect: The solubility of any compound is greatly reduced if one of the ions that make up the compound is already present in the solution. Example: The solubility of PbCl2 is greatly reduced when NaCl is added to the solution. Drill: Calculate the solubility & the maximum molarity of all ions in a solution of MZ3. (Ksp for MZ3 = 2.7 x 10-19) Calculate Solubility of Each: MQ2: Ksp = 3.2 x 10-11 MZ3: Ksp = 2.7 x 10-15 CaCO3: Ksp = 4.4 x 10-16 Drill: Calculate the solubility of M3Q4 (Ksp for M3Q4= 6.9 x 10-207) Solubility Concepts: Rxn: AgI(s) Ag+ + I Ksp = [Ag+][I-] at Eq. Qsp = [Ag+][I-] init. As with equilibrium constants earlier, Q has the same formula, but refers to the start of a reaction rather than equilibrium If Qsp > Ksp , a precipitate will form If Qsp < Ksp , no precipitate will form Problem: 150 mL 0.0010 M KI is added to 100 mL 0.050 M Pb(NO3)2. (Ksp for PbI2 = 8.0 x 10-9) • Will a ppt form? Problem: 300.0 mL 0.0010 M KQ is added to 200.0 mL 0.050 M MX2. (Ksp for MQ2 = 6.0 x 10-9) • Will a ppt form? Drill: Calculate the solubility of AgI(s) (Ksp = 1.5 x 10-16) Common Ion Effect: Solubility of a solid is reduced when one of its ions is already in solution Common Ion Solubility Calculation Demonstration: • Calculate the solubility of AgI(s) in 0.10 M NaI : 1. Set up & balance rxns: 2. Assign Eq. amounts: 3. Write Keq: 4. Substitute: 5. Solve for x: (Ksp = 1.5 x 10-16) AgI(s) Ag+ + I1–x x x NaI(s) Na+ + I0.10 – all 0.10 0.10 Ksp = [Ag+][I-] Ksp = [x][0.10 + x] Ksp = 0.10x = 1.5 x 10-16 x = solubility = 1.5 x 10-16 M Problems: • Calculate the solubility of MZ2(s) in 0.20 M M(NO3)2: (Ksp = 2.0 x 10-15) • 30.0 mL 0.0010 M KBr is added to 20.0 mL 0.050 M Y(NO3)2. (Ksp for YBr2 = 6.0 x 10-9) Will a ppt. form? Drill: 10.0 mL 0.050 M KCl is added to 15 mL 0.075 M Pb(NO3)2. (Ksp PbCl2 = 1.7 x 10-5) Will a ppt form? Problems: • Calculate the solubility of Al(OH)3(s) in 0.20 M Al(NO3)3: • Calculate the solubility of PbI2(s) in 0.010 M NaI : • Calculate the solubility of CaCO3 in water: Drill: Calculate the solubility of PbS(s) in water: (Ksp = 2.0 x 10-33) (Ksp = 3.2 x 10-8) ( Ksp = 4.9 x 10-15) ( Ksp = 1.0 x 10-28) Multiple Common Ion Problem Demonstration: Problem: Aqueous NaI is added (dropwise) to a solution of 0.10 M AgNO3 & 0.20 M CuNO3 . (AgI Ksp = 1.0 x 10-16)(CuI Ksp = 5.1 x 10-12) What substance precipitates 1st ? A) Determine all ions present in solution: B) Determine the concentration of each ion NaI Na+ + I? ? ? AgNO3 Ag+ + NO30.10 – all 0.10 0.10 CuNO3 Cu+ + NO30.20 – all 0.20 0.20 Perform equilibrium calculations with ions that appear in the Ksp’s that were given: 1) 2) 3) 4) Set up & balance rxn: Assign Eq. amounts: Write the Keq’s: Substitute: 5) Solve for x: The solubility of AgI < CuI AgI Ag+ + I0.10 – x x x + Ksp1 = [Ag ][ I ] Ksp1 = [0.10 + x][ x] Ksp1 = 0.10 x 0.10 x = 1.0 x 10-16 x = 1.0 x 10-15 M x = 1.0 x 10-15 M > CuI Cu+ + I0.20 – y y y Ksp2 = [0.20 + y][ y] Ksp2 = [0.20 + y][ y] drop x & y Ksp2 = 0.20 y 0.20 y = 5.1 x 10-12 y = 2.6 x 10-11 M y = 2.6 x 10-11 M Thus AgI ppts. 1st Problem: Aqueous Kcl is added (dropwise) to a solution of 0.10 M AgNO3 & 0.20 M Cu(NO3)2 . (AgCl Ksp = 1.8 x 10-10) (CuCl2 Ksp = 2.4 x 10-16) What substance precipitates 1st ? • Calculate the solubility of PbCl2(s): Drill: Calculate the solubility of Sc(OH)3(s): (Ksp = 1.6 x 10-5) (Ksp = 2.7 x 10-31) Test Review Problems: • Calculate the solubility of AgI(s) : (Ksp = 1.5 x 10-16) • Calculate the solubility of AgI(s) in 0.20 M NaI : (Ksp = 1.5 x 10-16) • Calculate the solubility of MgZ2(s): (Ksp = 4.0 x 10-15) • The solubility of Ca(OH)2 = 4.0 x 10-6 M. Calculate its Ksp : • Aqueous MgCl2 is added (dropwise) to a solution of 0.20 M KOH & 0.10 M K2SO4. (Mg(OH)2 Ksp = 5.0 x 10-6) (MgSO4 Ksp = 5.6 x 10-5) What ppts. 1st ? 10.0 mL 0.050 M KCl is added to 15 mL 0.060M Pb(NO3)2.(Ksp PbCl2 = 1.7 x 10-5) Will a ppt form?

Download
# PP 25: Solubility Equilibria