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Reactions of Acids & Bases

Reactions of Acids & Bases. H 2 O + H 2 O H 3 O + + OH -. Self-Ionization of Water. In pure water at 25 ºC, both H 3 O + and OH - ions are found at concentrations of 1.0 x 10 -7 M. K w = [H 3 O + ][OH - ] = 1.0  10 -14.

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Reactions of Acids & Bases

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  1. Reactions of Acids & Bases

  2. H2O + H2O H3O+ + OH- Self-Ionization of Water • In pure water at 25ºC, both H3O+ and OH- ions are found at concentrations of 1.0 x 10-7 M. Kw = [H3O+][OH-] = 1.0  10-14

  3. In all solutions at 25ºC, the product of the concentrations of H3O+ and OH- ions is equal to 1.0 x 10-14 M.

  4. It’s an acid … if [H3O+] > 1.0  10-7

  5. It’s a base … if [OH-] > 1.0  10-7

  6. It’s neutral … if [H3O+] = [OH-] = 1.0  10-7

  7. pouvoir hydrogène (Fr.) “hydrogen power” pH Scale 14 0 7 INCREASING BASICITY INCREASING ACIDITY NEUTRAL pH = -log[H3O+]

  8. pH Scale pH of Common Substances

  9. pH Scale The pH scale runs from 0 to 14, but each unit represents a tenfold change in the concentration. The H3O+ concentration of 1 x 100 is not 14 times a concentration of 1 x 10-14, but it is a factor of 1014, which is 100 trillion times!

  10. pH Scale

  11. Practice Problem #1 • What is the concentration of OH- ions in saturated lime if [H3O+] = 3.98 x 10-13 M? Is lime acidic, basic, or neutral? [H3O+][OH-] = 1.0  10-14 [3.98  10-13][OH-] = 1.0  10-14 [OH-] = 2.5  10-2 M or 0.025 M BASIC [OH-] > 1.0  10-7

  12. Practice Problem #11 • Analysis of a sample of maple syrup reveals that the concentration of OH- ions is 5.0 x 10-8 M. What is the pH? Is it acidic, basic, or neutral? [H3O+][OH-] = 1.0  10-14 [H3O+][5.0 x 10-8] = 1.0  10-14 [H3O+] = 2.0  10-7 M Acidic pH = 6.7 pH = -log[H3O+]

  13. More Sample Problems • What is the pH of 0.080 M HNO3? • What is the [H3O+] and the [OH-]? [H3O+][OH-] = 1.0 x 10-14 [H3O+] = 0.080 M [ OH-] = 1.0 x 10-14 pH = -log[H3O+] pH = -log[0.080] pH = 1.1 [H3O+] [ OH-] = 1.3 x 10-13 Acidic

  14. More Sample Problems • What is the pH of 0.0123 M H2SO4? • What is the [H3O+] and the [OH-]? [H3O+] = 2(0.0123) M = 0.0246 M pH = -log[H3O+] pH = -log[0.0246] pH = 1.61 [H3O+][OH-] = 1.0 x 10-14 [ OH-] = 1.0 x 10-14 [H3O+] Acidic [ OH-] = 4.07 x 10-13

  15. More Sample Problems • The pH of a solution is 4.29 • What is the [H3O+] and the [OH-]? pH = -log[H3O+] [H3O+][OH-] = 1.0 x 10-14 10 = [H3O+] -pH [ OH-] = 1.0 x 10-14 [H3O+] [H3O+] = 5.13 x 10-5 Acidic [ OH-] = 1.95 x 10-10

  16. Buffers

  17. A buffer is a mixture that is able to release or absorb H+ ions, keeping a solution’s pH constant.

  18. Most common buffers are mixtures of weak acids and their conjugate bases.

  19. Example Acetic acid and acetate ion H3O+ + C2H3O2 - H2O + HC2H3O2 When H3O+ ions are added to this solution, they react with the acetate ion. pH changes only slightly

  20. Example Acetic acid and acetate ion OH- + HC2H3O2H2O + C2H3O2 - When OH- ions are added to this solution, they react with the acetic acid. pH changes only slightly

  21. All buffers have a limited capacity to neutralize added H3O+ or OH- ions. • Buffer Capacity is the amount of acid or base that a buffer can neutralize.

  22. If you add H3O+ or OH- ions beyond the buffer capacity, the ions will remain in solution, and the pH will change.

  23. The greater the concentration of buffer in the solution, the greater the buffer capacity.

  24. The human body must maintain the pH of blood between 7.35 and 7.45. • A pH outside this range can cause extreme illness or death.

  25. Section 19-3 Acid-Base Titration

  26. standard solution unknown solution Titration • An acid base titration is a carefully controlled neutralization reaction. • Find concentration of an unknown solution by using a known “standard” solution

  27. Titration • Equivalence point • When enough standard solution is added to neutralize all the acid or base in the unknown solution. • dramatic change in pH • Determined by the Endpoint • indicator color change

  28. Titration • Strong Acid with Strong Base • Equivalence Point: pH = 7 • phenolphthalein

  29. Titration • Weak Acid with Strong Base • Equivalence Point: pH > 7 • Phenolphthalein

  30. Titration • Weak Base with Strong Acid • Equivalence Point: pH < 7 • Methyl red

  31. Titration moles H3O+ = moles OH- MV#a = MV#b M: Molarity V: volume #: # of H+ ions in the acid or OH- ions in the base

  32. Titration • 42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H2SO4. Find the molarity of H2SO4. H3O+ M = ? V = 50.0 mL n = 2 OH- M = 1.3M V = 42.5 mL n = 1 MV#a= MV#b M(50.0mL)(2) =(1.3M)(42.5mL)(1) M = 0.55M H2SO4

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