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Chapter 17: Additional Aspects of Aqueous Equilibria

Chapter 17: Additional Aspects of Aqueous Equilibria. Molar Solubility:. The number of moles of solute that will dissolve per liter of solution. x. x. x. 15.40 Consider the reaction: CaSO 4 ( s ) ⇋ Ca 2+ ( aq ) + SO 4 2- ( aq ) At 25  C, K c = 2.4 × 10 -5 for this reaction.

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Chapter 17: Additional Aspects of Aqueous Equilibria

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  1. Chapter 17: Additional Aspects of Aqueous Equilibria Molar Solubility: The number of moles of solute that will dissolve per liter of solution x x x 15.40 Consider the reaction: CaSO4(s) ⇋ Ca2+(aq) + SO42-(aq) At 25C, Kc= 2.4 × 10-5 for this reaction. (a) If excess CaSO4(s) is mixed with water at 25°C to produce a saturated solution of CaSO4, what are the equilibrium concentrations of Ca2+ and SO42-? Ksp=[Ca2+][SO42-] 2.4 x 10-5 = x2 x = 4.9 x 10-3 M 4.9 x 10-3 moles of CaSO4 will dissolve per liter of solution

  2. (b) If the resulting solution has a volume of 3.0 L, what is the minimum mass of CaSO4(s) needed to achieve equilibrium? (4.9 x 10-3 mol/L)(3.0 L) = 0.015 moles CaSO4 x 136.142 g/mol 2.0 g of CaSO4 Q: What is the molar solubility of CaSO4 if enough CaCl2 is added to make [Ca2+] = 0.10 M? The addition of an ion that is involved with the equilibrium (a common ion), causes a left shift in the equilibrium and reduces the solubility of the solute x 0.10 M x CaSO4(s) ⇋ Ca2+(aq) + SO42-(aq) Ksp=[Ca2+][SO42-] 2.4 x 10-5 =[0.10 M ][x]  the Common Ion Effect x = 2.4 x 10-4 M

  3. Predicting Precipitates = 1.3 x 10-15 (Appendix D) 17.52 (a) Will Co(OH)2 precipitate from solution if the pH of a 0.020 M solution of Co(NO3)2 is adjusted to 8.5? Equilibrium involved: Co(OH)2(s)⇋ Co2+(aq) + 2 OH(aq) Ksp = [Co2+][OH]2 Recall that pH + pOH = 14, so pOH = 5.5 [Co2+] = 0.020 M [OH] = 10pOH = 105.5 = 3.16 x 10-6 M Find Qsp = [Co2+][OH]2 = [0.020 M][3.16 x 10-6 M]2 = 2.0 x 10-13 Because Qsp > Ksp, a precipitate will form

  4. Formation of Complex Ions Ag+(aq) + 2 NH3(aq)⇋ Ag(NH3)2+ • Most transition metal ions are capable of forming complex ions. • A complex ion consists of a cationic metal center and 2, 4 or 6 ligands. • The ligands form a coordinate covalent bond with the metal center by sharing a lone pair on the ligand with an empty d-orbital on the metal center. Kf = 1.7 x 107 Kf =

  5. Ag forms complexes with 2 ligands • Fe forms complexes with 6 ligands • Most of the other TM cations form complexes with 4 ligands

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