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

Drill: A 0.100 M solution of HZ ionizes 20.0 %. Calculate: K aHZ. Buffer Solutions. Buffer Solution. A solution that resists changes in pH. Buffer Solution. Made from the combination of a weak acid & its salt. Buffer Solution. Made from the combination of a weak base & its salt.

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

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  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

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

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

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

  44. 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

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