1. Brønsted-Lowry definition of an acid: An acid is a proton donor. 721

2. Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. 722

3. Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. H + (aq) + OH - (aq) H 2 O (l) acid base 723

4. Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. H + (aq) + OH - (aq) H 2 O (l) acid base HCl (g) + NH 3(g) NH 4 Cl (s) acid base 724

5. Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. H + (aq) + OH - (aq) H 2 O (l) acid base HCl (g) + NH 3(g) NH 4 Cl (s) acid base Note in this latter example, there is no water present. 725

6. Strong and Weak Acids: 726

7. Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) 727

8. Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) 728

9. Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) K c is large – the concentration of HBr at equilibrium is very small. 729

10. Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) K c is large – the concentration of HBr at equilibrium is very small. The size of K c can be used to indicate the strength of an acid, but there is a more convenient way to represent data on acid strengths, which will be treated shortly. 730

11. HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) 731

12. HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) 732

13. HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) K c for this acid is small. This means the concentration of H 3 O + at equilibrium is small. 733

14. HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) K c for this acid is small. This means the concentration of H 3 O + at equilibrium is small. HF (aq) is a weak acid. 734

15. HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) K c for this acid is small. This means the concentration of H 3 O + at equilibrium is small. HF (aq) is a weak acid. Note that a weak acid can be corrosive. HF (aq) is a very corrosive acid – it attacks glass. 735

16. Strong and weak bases. NH 2 - + H 2 O (l) NH 3(aq) + OH - (aq) 736

17. Strong and weak bases. NH 2 - + H 2 O (l) NH 3(aq) + OH - (aq) amide ion 737

18. Strong and weak bases. NH 2 - + H 2 O (l) NH 3(aq) + OH - (aq) amide ion K c for this reaction is large, indicating the amide ion is a strong base. 738

19. Strong and weak bases. NH 2 - + H 2 O (l) NH 3(aq) + OH - (aq) amide ion K c for this reaction is large, indicating the amide ion is a strong base. NH 3(g) + H 2 O (l) NH 4 + (aq) + OH - (aq) 739

20. Strong and weak bases. NH 2 - + H 2 O (l) NH 3(aq) + OH - (aq) amide ion K c for this reaction is large, indicating the amide ion is a strong base. NH 3(g) + H 2 O (l) NH 4 + (aq) + OH - (aq) K c for this reaction is small, indicating that NH 3 is a weak base. 740

21. Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. 741

22. Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - 742

23. Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O 743

24. Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O base in this reaction 744

25. Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O base in this reaction HCO 3 - (aq) + OH - (aq) CO 3 2- (aq) + H 2 O 745

26. Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O base in this reaction HCO 3 - (aq) + OH - (aq) CO 3 2- (aq) + H 2 O acid in this reaction 746

27. Amphiprotic: A substance that can function as an acid or a base. 747

28. Conjugate acid-base relationships 748

29. Conjugate acid-base relationships Consider the equilibrium: HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) 749

30. Conjugate acid-base relationships Consider the equilibrium: HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) conjugate acid-base pair 750

31. Conjugate acid-base relationships Consider the equilibrium: conjugate acid-base pair HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) conjugate acid-base pair 751

32. Conjugate acid-base relationships Consider the equilibrium: conjugate acid-base pair HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) conjugate acid-base pair The formulas of any conjugate acid-base pair differ only by one H +. CN - is a base, because of the reaction: 752

33. H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O 753

34. H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base 754

35. H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: 755

36. H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: acid 1 + base 2 acid 2 + base 1 756

37. H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: acid 1 + base 2 acid 2 + base 1 757

38. H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: acid 1 + base 2 acid 2 + base 1 758

39. 759

40. Self-Dissociation of Water 760

41. Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: 761

42. Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: H 2 O + H 2 O H 3 O + (aq) + OH - (aq) 762

43. Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: H 2 O + H 2 O H 3 O + (aq) + OH - (aq) The position of this equilibrium lies strongly on the left (at 25 o C): 763

44. Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: H 2 O + H 2 O H 3 O + (aq) + OH - (aq) The position of this equilibrium lies strongly on the left (at 25 o C): 764

45. At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M, and [H 2 O] = 55.5 M. 765

46. At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: 766

47. At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: 767

48. At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: Now set K w =, so that at 25 o C 768

49. At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: Now set K w =, so that at 25 o C 769

50. At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: Now set K w =, so that at 25 o C The w subscript refers to water. 770

51. Criteria for Acidic, Basic, and neutral solutions 771

52. Criteria for Acidic, Basic, and neutral solutions Neutral solution: [H 3 O + ] = [OH - ] 772

53. Criteria for Acidic, Basic, and neutral solutions Neutral solution: [H 3 O + ] = [OH - ] Acidic solution: [H 3 O + ] > [OH - ] 773

54. Criteria for Acidic, Basic, and neutral solutions Neutral solution: [H 3 O + ] = [OH - ] Acidic solution: [H 3 O + ] > [OH - ] Basic solution: [H 3 O + ] < [OH - ] 774

55. The pH concept 775

56. The pH concept To avoid awkward numbers such as 9.2 x 10 -11 when dealing with H 3 O + concentrations, the following concept is employed: 776

57. The pH concept To avoid awkward numbers such as 9.2 x 10 -11 when dealing with H 3 O + concentrations, the following concept is employed: pH = - log[H + ] 777

58. The pH concept To avoid awkward numbers such as 9.2 x 10 -11 when dealing with H 3 O + concentrations, the following concept is employed: pH = - log[H + ] This is actually shorthand for pH = - log([H + ]/M) 778

59. The exact definition of pH is The exact definition of pH is: 779

60. The exact definition of pH is The exact definition of pH is: is called the activity of the hydrogen ion. 780