Drill: A 0.100 M solution of HZ ionizes 20.0 %. Calculate: K aHZ

1. Drill: A 0.100 M solution of HZ ionizes 20.0 %.Calculate: KaHZ

2. Buffer Solutions

3. Buffer Solution • A solution that resists changes in pH

4. Buffer Solution • Made from the combination of a weak acid & its salt

5. Buffer Solution • Made from the combination of a weak base & its salt

6. Buffer Examples • Mix acetic acid & sodium acetate • Mix ammonia & ammonium chloride

7. Buffer Solution • A buffer solution works best when the acid to salt ratio is • 1 : 1

8. Buffer Solution • A buffer solution works best when the base to salt ratio is • 1 : 1

9. Buffer Solution • The buffering capacity of a solution works best when the pH is near the pKa

10. pKa or pKb • pKa = - log Ka • pKb = - log Kb

11. BufferEquilibria

12. To solve buffer equilibrium problems, use the same 5 steps

13. 5 Steps of Equilibrium Problems 1) Set up & balance reaction

14. 5 Steps of Equilibrium Problems 2) Assign Equilibrium amounts in terms of x (ICE)

15. 5 Steps of Equilibrium Problems 3) Write the equilibrium expression (K = ?)

16. 5 Steps of Equilibrium Problems 4) Substitute Equilibrium amounts into the K

17. 5 Steps of Equilibrium Problems 5) Solve for x

18. Buffer Problems • Calculate the pH of a solution containing • 0.10 M HAc in 0.10 M NaAc: Ka = 1.8 x 10-5

19. Buffer Problems • Calculate the pH of 0.10 M NH3 in • 0.20 M NH4NO3: • Kb = 1.8 x 10-5

20. Buffer Problems Calculate the pH of a solution containing 0.10 M HBz in 0.20 M NaBz: Ka = 6.4 x 10-5

21. Drill: Calculate the pH of a solution containing 0.30 M HZ in 0.10 M NaZ: Ka = 3.0 x 10-5

22. Buffer Problem Calculate the pH of a solution containing 0.50 M R-NH2 in 0.10 M R-NH3I: Kb = 4.0 x 10-5

23. Derivations from an equilibrium constant

24. HA H+ + A- [H+][A-] [HA] Ka =

25. HA H+ + A- [H+][A-] [HA] Ka = Cross multiply to isolate [H+]

26. HA H+ + A- [Ka][HA] [A-] [H+]=

27. HA H+ + A- [HA] [A-] [H+] = (Ka)

28. HA H+ + A- [HA] [A-] [H+] = (Ka) Take –log of each side

29. pH = [HA] [A-] pKa - log

30. Henderson-Hasselbach Eq [A-] [HA] pH = pKa + log

31. Henderson-Hasselbach Eq [B+] [B] pOH = pKb+ log

32. Buffer Problems • Calculate the salt to acid ratio to make a buffer solution with pH = 5.0 • Ka for HBZ = 2.0 x 10-5

33. Derivations from an equilibrium constant

34. HA H+ + A- [H+][A-] [HA] Ka =

35. [H+][A-] [HA] Ka = Divide both sides by [H+]

36. Ka [A-] [H+] [HA] = You Get the Salt to Acid Ratio

37. Drill: • Calculate the salt to acid ratio to make a buffer solution with pH = 5.0 • Ka for HBZ = 2.0 x 10-5

38. Buffer Problems • Calculate the salt to base ratio to make a buffer solution with pH = 9.48 • Kb for MOH = 2.0 x 10-5

39. Equivalence Point Point at which the # of moles of the two titrants are equal

40. Titration Curves

42. [HA]=[OH-] [HA]=[A-]

43. Drill: Calculate the pH of a buffer solution containing 0.50 M HX in 0.25 M KX. Ka = 2.5 x 10-5

45. Calculate the HCO3- to H2CO3 ratio in blood with pH = 7.40 • Ka1 for H2CO3 = 4.4 x 10-7

46. 150 ml of 0.10 M NaOH is added to 100.0 ml of 0.10 M H2CO3. Calculate pH. • Ka1 for H2CO3 = 4.4 x 10-7 • Ka2 for H2CO3 = 4.8 x 10-11