1. Copyright McGraw-Hill 20091 Chapter 16 Acids and Bases Insert picture from First page of chapter

2. Copyright McGraw-Hill 20092 16.1 Brønsted Acids and Bases Acid – proton donor Base – proton acceptor Conjugate base – what remains of the acid after the donation of a proton Conjugate acid – newly formed protonated species (base)

3. Copyright McGraw-Hill 20093 Conjugate Acid-Base Pairs

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5. 5 16.2 The Acid-Base Properites of Water Autoionization of water – water is amphoteric, can act as an acid or base or

6. Copyright McGraw-Hill 20096 For pure water at 25 o C Relative amounts determine if the solution is acid, base, or neutral. When [H 3 O + ] = [OH  ], the solution is neutral. When [H 3 O + ] > [OH  ], the solution is acidic. When [H 3 O + ] < [OH  ], the solution is basic.

7. Copyright McGraw-Hill 20097 16.3 The pH Scale or pH Meter: Laboratory Measurement of pH

8. Copyright McGraw-Hill 20098 Relative amounts determine if the solution is acid, base, or neutral. When pH = 7, the solution is neutral. When pH < 7.00, the solution is acidic. When pH > 7.00, the solution is basic.

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11. Copyright McGraw-Hill 200911 1.What is the pH of a solution that has a hydronium ion concentration of 6.5 x 10  5 M? 2. What is the hydronium ion concentration of a solution with pH 3.65?

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13. Copyright McGraw-Hill 200913 Relations among pH, [OH  ], pOH, and K w

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15. Copyright McGraw-Hill 200915 1. What is the pOH of a solution that has a hydroxide ion concentration of 4.3 x 10  2 M? 2. What is the hydroxide ion concentration of a solution with pOH 8.35?

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17. Copyright McGraw-Hill 200917 16.4 Strong Acids and Bases Ionization or dissociation goes to completion – not considered an equilibrium process Concentration of ions in solution is determined by the stoichiometry of the reaction only –[H 3 O + ] is equal to starting concentration of the acid –[OH  ] is equal to starting concentration of the base (stoichiometry must be considered) Only a few acids and bases are strong

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20. Copyright McGraw-Hill 200920 What is the pH of a 0.057 M solution of HBr?

21. Copyright McGraw-Hill 200921 HBr completely ionizes, and the [H 3 O + ] is equal to the initial concentration of HBr.

22. Copyright McGraw-Hill 200922 What is the pOH of a solution of 0.034 M solution of Ca(OH) 2 ?

23. Copyright McGraw-Hill 200923 Ca(OH) 2 completely ionizes, and the [OH  ] is equal to twice the initial concentration of Ca(OH) 2.

24. Copyright McGraw-Hill 200924 16.5 Weak Acids and Acid Ionization Constants Weak acids ionize only to a limited extent in water. The degree to which a weak acid ionizes depends on –the concentration of the acid –the equilibrium constant for the ionization called the acid ionization constant, K a.

25. Copyright McGraw-Hill 200925 or For a generic weak monoprotic acid

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27. Copyright McGraw-Hill 200927 Format for solving problems of weak acids using an equilibrium table Fill in initial concentrations Determine concentration changes in terms of x Determine equilibrium concentrations in terms of initial concentrations (C i ) and x Substitute into the K a expression and solve for x

28. Copyright McGraw-Hill 200928 which produces a quadratic expression of the form: If the initial concentration and K a allow, the expression can be simplified by assuming that x is insignificant when compared to C i.

29. Copyright McGraw-Hill 200929 Testing the approximation – it is acceptable to use this shortcut if the calculated value of x is less than 5 percent of the initial acid concentration.

30. Copyright McGraw-Hill 200930 Calculate the pH at 25°C of a 0.18 M solution of a weak acid that has K a = 9.2 x 10  6.

31. Copyright McGraw-Hill 200931 00 0.18 M +x −x−x 0.18 M − x xx Use the approximation since K a is small compared to C i.

32. Copyright McGraw-Hill 200932 Check the approximation: Approximation is valid.

33. Copyright McGraw-Hill 200933 16.6 Weak Bases and Base Ionization Constants Weak bases ionize only to a limited extent in water. The degree to which a weak base ionizes depends on –the concentration of the base –the equilibrium constant for the ionization called the base ionization constant, K b.

34. Copyright McGraw-Hill 200934 For a generic weak base Solving problems involving weak bases requires the same approach as for weak acids. Solving for x in a typical weak base problem gives the hydroxide ion concentration rather than the hydronium ion concentration.

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36. Copyright McGraw-Hill 200936 Determine the K b of a weak base if a 0.50 M solution of the base has a pH of 9.59 at 25°C.

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38. Copyright McGraw-Hill 200938 0 M 0.050 M +3.89x10 -5 M 3.89x10 -5 M − 3.89x10 -5 M 0.050 M*

39. Copyright McGraw-Hill 200939 16.7 Conjugate Acid-Base Pairs The conjugate base of a strong acid, is an example of a weak conjugate base. The conjugate base of a weak acid, is an example of a strong conjugate base. Conversely, a strong base has a weak conjugate acid and a weak base has a strong conjugate acid.

40. Copyright McGraw-Hill 200940 Reciprocal Relationship Between the Strength of an Acid or Base and the Strength of its Conjugate Quantitative Relationship Between K a and K b

41. Copyright McGraw-Hill 200941 Determine K b of the benzoate ion (C 6 H 5 COO  ).

42. Copyright McGraw-Hill 200942 Benzoate ion is the conjugate base of benzoic acid.

43. Copyright McGraw-Hill 200943 16.8 Diprotic and Polyprotic Acids Diprotic and polyprotic acids undergo successive ionizations, losing one proton at a time The conjugate base in the first ionization is the acid in the second ionization. Each ionization has a K a associated with it. Ionization constants are designated by the step in the ionization involved.

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45. Copyright McGraw-Hill 200945 Calculate the concentrations of H 2 C 2 O 4, HC 2 O 4 , C 2 O 4 2 , and H + ions in a 0.20 M oxalic acid solution at 25°C.

46. Copyright McGraw-Hill 200946 − x− x+x+x +x+x 0.20 M 0.20 M − x x x [H + ]=0.086 M [HC 2 O 4 + ]=0.086 M [H 2 C 2 O 4 ]=0.20 M − 0.086 M = 0.11 M

47. Copyright McGraw-Hill 200947 [H + ] = 0.086 M [HC 2 O 4  ] = 0.086 M [C 2 O 4 2  ] = 6.1 x 10  5 M − y− y+y+y +y+y 0.086 M 0.086 M − y 0.086 M + y y 0.086 M

48. Copyright McGraw-Hill 200948 16.9 Molecular Structure and Acid Strength The strength of an acid is measured by its tendency to ionize. Two factors influence the extent to which the acid undergoes ionization. –the strength of the bond –polarity of the bond

49. Copyright McGraw-Hill 200949 Types of Acids Hydrohalic Acids – binary acids formed between hydrogen and the halogens –the predominant factor in determining the strength of the hydrohalic acids is bond strength HF << HCl < HBr < HI

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51. Copyright McGraw-Hill 200951 Oxoacids - contain hydrogen, oxygen, and a central, nonmetal atom –contain one or more bonds –an electronegative or a high oxidation state central atom, will attract electrons, causing the bond to be more polar –high electronegativity and oxidation result in stronger acids

52. Copyright McGraw-Hill 200952 To compare oxyacid strengths Oxoacids having different central atoms that are from the same group of the periodic table and that have the same oxidation number. –acid strength increases with increasing electronegativity of the central atom Example:

53. Copyright McGraw-Hill 200953 Oxoacids having the same central atom but different numbers of oxygen atoms –strength increases with increasing oxidation number of the central atom Example:

54. Copyright McGraw-Hill 200954 Carboxylic acids – organic acids with the structure –Ionize to produce a carboxylate anion –Increasing stability of the carboxylate anion increases acidity Stability increases with the number of electronegative groups in the R group

55. Copyright McGraw-Hill 200955 Indicate which is the stronger acid: (a) HBrO 3 or HBrO 4 ; (b) H 2 SeO 4 or H 2 SO 4.

56. Copyright McGraw-Hill 200956 b) In a group with different central atoms, we must compare electronegativities. The electronegativities of the central atoms in this group decrease as follows: S>Se. H 2 SO 4 > H 2 SeO 4 a)These two acids have the same central atom but differ in the number of attached oxygen atoms. In a group such as this, the greater the number of attached oxygen atoms, the higher the oxidation number of the central atom and the stronger the acid. HBrO 4 > HBrO 3

57. Copyright McGraw-Hill 200957 16.10 Acid-Base Properties of Salt Solutions Salt solutions are affected by salt hydrolysis, in which ions produced by the dissociation of a salt react with water to produce either hydroxide ions or hydronium ions—thus impacting pH. Basic salt solutions - an anion that is the conjugate base of a weak acid reacts with water to produce hydroxide ion.

58. Copyright McGraw-Hill 200958 Acidic salt solutions –When the cation of a salt is the conjugate acid of a weak base, a solution of the salt will be acidic. For example:

59. Copyright McGraw-Hill 200959 – Small, highly charged metal ions are hydrated by water molecules and polarization of one of the O-H bonds can produce hydrogen ions.

60. Copyright McGraw-Hill 200960 Determine the pH of a 0.25 M solution of pyridinium nitrate (C 5 H 5 NHNO 3 ) at 25°C. [Pyridinium nitrate dissociates in water to give pyridinium ions (C 5 H 5 NH + ), the conjugate acid of pyridine (K b = 1.7 x 10  9 ), and nitrate ions (NO 3  ).]

61. Copyright McGraw-Hill 200961 0.25 M −x−x+x+x +x+x x x 0.25 − x M

62. Copyright McGraw-Hill 200962 0.25 M − x+x+x +x+x x x 0.25 − x M

63. Copyright McGraw-Hill 200963 Neutral salt solutions –A salt composed of the cation of a strong base and the anion of a strong acid produces a neutral solution. –These ions do not hydrolyze in water. For example: NaCl or KNO 3

64. Copyright McGraw-Hill 200964 Summary

65. Copyright McGraw-Hill 200965 Salts in Which Both the Cation and the Anion Hydrolyze –pH depends on the relative strengths of the conjugate acid and base When K b > K a, the solution is basic. When K b < K a, the solution is acidic. When K b = K a, the solution is neutral or nearly neutral. NH 4 NO 2 For example:

66. Copyright McGraw-Hill 200966 Predict whether 0.10 M solutions of the following are acidic, basic or nearly neutral. a) C 5 H 5 CNHCl b) KF

67. Copyright McGraw-Hill 200967 a) C 5 H 5 CNHCl b) KF acidic basic

68. Copyright McGraw-Hill 200968 16.11 Acid-Base Properties of Oxides and Hydroxides

69. Copyright McGraw-Hill 200969 Basic metallic oxides react with water to form metal hydroxides. Acidic nonmetallic oxides react with water to form acids.

70. Copyright McGraw-Hill 200970 Basic and Amphoteric Hydroxides –All the alkali and alkaline earth metal hydroxides, except Be(OH) 2, are basic. –Be(OH) 2, as well as Al(OH) 3, Sn(OH) 2, Pb(OH) 2, Cr(OH) 3, Cu(OH) 2, Zn(OH) 2, and Cd(OH) 2, are amphoteric and insoluble in water. –React with acids –React with bases

71. Copyright McGraw-Hill 200971 16.12 Lewis Acids and Bases Lewis base as a substance that can donate a pair of electrons. Lewis acid is a substance that can accept a pair of electrons. A Lewis acid-base reaction is one that involves the donation of a pair of electrons from one species to another. Most general definition of acids and bases

72. Copyright McGraw-Hill 200972 coordinate covalent bond A Lewis Acid-Base Reaction

73. Copyright McGraw-Hill 200973 Key Points Br Ø nsted acids and bases –Conjugate acid –Conjugate base Acid-base properties of water –Autoionization of water –K w –Relation between hydronium and hydroxide ion concentrations

74. Copyright McGraw-Hill 200974 The pH scale –Defining equation –pOH scale –Relation among pH, pOH and K w Strong acids and bases Weak acids and acid ionization constants –Definition of weak acids –K a, the acid ionization (equilibrium) constant –Method to solve weak acid equilibrium problems

75. Copyright McGraw-Hill 200975 Weak bases and base ionization constants –Definition of weak bases –K b, the base ionization (equilibrium) constant –Method to solve weak base equilibrium problems Conjugate acid-base pairs –Strength of acid-base pairs –Relation between K a and K b for conjugate pairs Diprotic and triprotic Acids –Successive ionization steps –Associated K a values –Solving equilibrium problems

76. Copyright McGraw-Hill 200976 Molecular structure and acid strength –Hydrohalic acids –Oxoacids –Carboxylic acids Acid-base properties of salt solutions –Basic salts –Acidic salts –Neutral salts –Complex salts in which both ions hydrolyze

77. Copyright McGraw-Hill 200977 Acid-base properties of oxides and hydroxides –Oxides Metal Nonmetal –Basic and amphoteric hydroxides Lewis acids and bases