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Outline: 3/12/07

Outline: 3/12/07. Chem. Dept. Seminar Wed @ 4pm 2 more lectures until Exam 2 … Chemistry Advising – Today @ 4pm. Today: More Chapter 18. Polyprotic acid titrations Solubility Product (K sp ). Worksheet #8 practice…. #1a. pH = 2.5

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Outline: 3/12/07

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  1. Outline: 3/12/07 • Chem. Dept. Seminar Wed @ 4pm • 2 more lectures until Exam 2… • Chemistry Advising – Today @ 4pm Today: • More Chapter 18 Polyprotic acid titrations Solubility Product (Ksp)

  2. Worksheet #8 practice… #1a. pH = 2.5 [H2A] = 0.997 M [HA-] = 0.00316 M [A2-] = 1  10-8 M #1b. pH = 10.5 #2a. pH = 9.74 #2b. pH = 11.1

  3. Quiz # 7 Please put away all books/papers If you don’t have a calculator, just set up the problems fully…

  4. Quiz # 7 Please turn your papers over and pass them to the right…

  5. Quiz #7 : Buffers #1 4.00 = 4.75 + log ([base]/[1.0M]) pH = pKa + log ([base]/[acid]) [base] = 10-0.75 = 0.178 M [base] = 0.178 mol/1.0L = 14.6 g CH3COONa / 1.0L

  6. Quiz #7 : Weak Base #2 0.015-x +x +x Pyr + H2O = pyrH+ + OH- Kb = 10-8.72 = 1.9110-9 1.9110-9 = x2 / 0.015 x = 5.34 10-6 = [OH-] pH = 14 – log( 5.34 10-6) = 8.73

  7. Quiz #7 : Titration #3 HA + OH- A- + H2O (titration) 0.0025 + 0.0005  0 + 0 (init) pH = pKa + log ([base]/[acid]) 0.0020 + 0  0.0005 (equil) pH = 3.74 + log ([0.0005]/[0.0020]) = 3.14

  8. Weak acid: Ka1 = x2/[H2A] Titration of Polyprotic Acids

  9. Buffer: pKa2+log[A]/[HA] Buffer: pKa1+log[HA]/[H2A] Titration of Polyprotic Acids

  10. log((Ka1× Ka2)0.5) See page 785 Titration of Polyprotic Acids

  11. Try example 18 – 12 (page 787) Sulfurous Acid, H2SO3, has two acidic hydrogen atoms, with pKa values of 1.85 and 7.20. Construct a titration curve for the titration of 125 mL of 0.150 M sulfurous acid with 0.800 M NaOH.

  12. Indicators • changes color as the titration passes the stoichiometric point if : pKin≈ pHstoichiometric point

  13. The Solubility-Product Constant, Ksp • Consider • for which • Ksp is the “solubility product”. (BaSO4 is ignored because it is a pure solid so its concentration is constant.)

  14. Solubility Equilibria • The solubility product is another example of equilibrium calculations • Solubility product calcs depend on the common ion effect (LeChâtelier). • They have particular applications with metal ions and pH calculations (environmental applications).

  15. Types of Equilibrium Constants: Lots of different names…. Keq, KH, Ksp, Ka , Kb, Kf , Kc, Kp… All the same idea!

  16. Solubility Equilibria • Insoluble compounds: solubility is less than 0.01 mol of dissolved material per liter of solution, Ksp << 1 • Slightly soluble: 10-5 < Ksp < 10-2 • Soluble: Ksp > 10-2

  17. Solubility Equilibria • The solubility product is another example of equilibrium calculations • Solubility product calcs depend on the common ion effect (LeChâtelier). • They have particular applications with metal ions and pH calculations (environmental applications).

  18. Factors that Affect Solubility • The Common Ion Effect • Solubility is decreased when a common ion is added (Le Châtelier again) • as F- (from NaF, say) is added, the equilibrium shifts left, therefore CaF2(s) is formed (precipitation occurs). • As NaF is added to the system, the solubility of CaF2 decreases.

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