www.hschemsolutions.com The Solubility Product (Ksp) • This is Keq for ionic compounds in water. Equilibrium 9.7 Ca2+(aq) + CO32-(aq) es CaCO3(s) The Solubility Product Constant (Ksp) Predicting Precipitates N ot Ksp = [Ca2+] [CO32-] Pb2+(aq) + 2Cl-(aq) PbCl2(s) ts 'L ec tu re Ksp = [Pb2+] [Cl-]2 Solubility Ex1) Solubility Product (Ksp) Ex1) The solubility product constant for lead (II) fluoride is 3.6 x 10-8 at 25oC. a) Write the balanced chemical equation. b) Write the equilibrium expression. c) Find the maximum molar concentrations of the ions in solution and the molar solubility of the solution. C op y of St ud • The solubility is the maximum molar concentration of formula units that will dissolve at a given temperature. – For every 1 mole of PbCl2(s) that dissolves, 1 mole of Pb2+(aq) ions and 2 moles of Cl-(aq) ions enter the solution. – Solubility of PbCl2 = [Pb2+] = ½ [Cl-] • when the solution is saturated. en Pb2+(aq) + 2 Cl-(aq) PbCl2(s) m pl e Ex1) Solubility Product (cont.) a) Sa b) c) Saturation and Equilibrium • Saturated Solution – The solvent has dissolved the maximum amount of solute that is can at a certain temperature, and some solid solute remains on the bottom. • A solution is at equilibrium when it is saturated. © 2009 High School Chem Solutions. All rights reserved. 1 www.hschemsolutions.com A Saturated Solution is at Equilibrium • The system is at equilibrium. • It is a saturated solution with solid and aqueous species. In a saturated solution, an equilibrium is created between the solid and aqueous states. +B ( aq ) es • The reaction will proceed to the left until the system reaches equilibrium. N ot Solids are constantly dissolving to form aqueous components, and aqueous components are solidifying at the same rate. If Q < Ksp, no precipitate forms. • The solution is unsaturated. • All of the ions will remain in solution. re ( aq ) − If Q > Ksp, a precipitate will form. ts 'L ec tu AB( s ) U A + Q and Ksp If Q = Ksp a) PbCl2(s) Pb2+(aq) + 2 Cl-(aq) ud a) Find Ksp for a saturated solution of PbCl2 if the concentration of Cl-(aq) is found to be 0.0325 M. Ex1) Predicting Possible Precipitates en Ex1) Predicting Possible Precipitates C op y of St b) Will a precipitate of PbCl2 form when 200.0mL of 3.78 x 10-2 M NaCl is mixed with 100.0mL of 2.45 x 10-2 M Pb(NO3)2. Assume that the temperature of the resulting solution is the same as that from part a. m pl e Ex1) Predicting Possible Precipitates b) Step 2, Find [Pb2+] Sa b) Step 1, Find [Cl-] Ex1) Predicting Possible Precipitates © 2009 High School Chem Solutions. All rights reserved. 2 www.hschemsolutions.com Ex1) Predicting Possible Precipitates Ex2) Predicting Precipitates b) Step 3, Find Q for the lead (II) chloride solution es Ex2) If 0.15 M NaOH is slowly poured into a beaker containing 0.14 M Ca(NO3)2 and 0.25 M Fe(NO3)2, which precipitate will form first? ts 'L ec tu re N ot Ksp for Ca(OH)2 = 8.0 x 10-6 Ksp for Fe(OH)2 = 1.6 x 10-14 Ex2) Predicting Precipitates (cont.) Ex2) Predicting Precipitates (cont.) Ca2+(aq) + 2 OH-(aq) Fe(OH)2(s) Fe2+(aq) + 2 OH-(aq) en Ca(OH)2(s) Step 2) Find [OH-]max for Fe(OH)2 Sa m pl e C op y of St ud Step 1) Find [OH-]max for Ca(OH)2 © 2009 High School Chem Solutions. All rights reserved. 3