1. Acids and Bases

2. Autoionization of Water and the pH Scale H 2 O( l ) H 3 O + ( aq )OH - ( aq ) + +

3. The nature of the hydrated proton.

4. Brønsted-Lowry Acid-Base Definition An acid is a proton donor, any species which donates a H +. A base is a proton acceptor, any species which accepts a H +.

5. Strong acid: HA( g or l ) + H 2 O( l ) H 2 O + ( aq ) + A - ( aq ) The extent of dissociation for strong and weak acids

6. Weak acid: HA( aq ) + H 2 O( l ) H 2 O + ( aq ) + A - ( aq )

7. The Acid-Dissociation Constant Weak acids dissociate very slightly into ions in water. Strong acids dissociate completely into ions in water. HA( g or l ) + H 2 O( l ) H 3 O + ( aq ) + A - ( aq ) HA( aq ) + H 2 O( l ) H 3 O + ( aq ) + A - ( aq ) K c >> 1 K c << 1 K c = [H 3 O + ][A - ] [H 2 O][HA] K c [H 2 O] = K a = [H 3 O + ][A - ] [HA] stronger acid higher [H 3 O + ] larger K a smaller K a lower [H 3 O + ] weaker acid

8. ACID STRENGTH Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9. K c = [H 3 O + ][OH - ] [H 2 O] 2 K c [H 2 O] 2 =[H 3 O + ][OH - ] The Ion-Product Constant for Water K w = A change in [H 3 O + ] causes an inverse change in [OH - ]. = 1.0 x 10 -14 at 25 0 C H 2 O( l ) + H 2 O( l ) H 3 O + ( aq ) + OH - ( aq ) In an acidic solution, [H 3 O + ] > [OH - ] In a basic solution, [H 3 O + ] < [OH - ] In a neutral solution, [H 3 O + ] = [OH - ]

10. The relationship between [H 3 O + ] and [OH - ] and the relative acidity of solutions. [H 3 O + ][OH - ] Divide into K w ACIDIC SOLUTION BASIC SOLUTION [H 3 O + ] > [OH - ] [H 3 O + ] = [OH - ][H 3 O + ] < [OH - ] NEUTRAL SOLUTION

11. The pH values of some familiar aqueous solutions pH = -log [H 3 O + ]

12. The relations among [H 3 O + ], pH, [OH - ], and pOH

13. Acid/Base ActivityCalculating [H 3 O + ], pH, [OH - ], and pOH PROBLEM:In a restoration project, a conservator prepares copper-plate etching solutions by diluting concentrated HNO 3 to 2.0M, 0.30M, and 0.0063M HNO 3. Calculate [H 3 O + ], pH, [OH - ], and pOH of the three solutions at 25 0 C.

15. Important pKa values to know CompoundStructurepKa Alkanes (sp 3 ) 51 Alkenes 44 Alkynes 25 Amines 33-35 Alcohols 15-19 Water 15.7 Carboxylic acids 3-5 Special Carboxylic acids -0.2 Strong Acids HBr HCl H 2 SO 4 -9 -7 -5.2 (first ionization)

16. Brønsted-Lowry Acid-Base Definition An acid-base reaction can now be viewed from the standpoint of the reactants AND the products. An acid reactant will produce a base product and the two will constitute an acid-base conjugate pair. An acid is a proton donor, any species which donates a H +. A base is a proton acceptor, any species which accepts a H +.

17. Proton transfer as the essential feature of a Brønsted-Lowry acid-base reaction (acid, H + donor)(base, H + acceptor) HClH2OH2O + Cl - H3O+H3O+ + Lone pair binds H + (base, H + acceptor)(acid, H + donor) NH 3 H2OH2O + NH 4 + OH - + Lone pair binds H +

18. The Conjugate Pairs in Some Acid-Base Reactions BaseAcid+ Base+ Conjugate Pair Reaction 4H 2 PO 4 - OH - + Reaction 5H 2 SO 4 N2H5+N2H5+ + Reaction 6HPO 4 2- SO 3 2- + Reaction 1HFH2OH2O+F-F- H3O+H3O+ + Reaction 3NH 4 + CO 3 2- + Reaction 2HCOOHCN - +HCOO - HCN+ NH 3 HCO 3 - + HPO 4 2- H2OH2O+ HSO 4 - N 2 H 6 2+ + PO 4 3- HSO 3 - +

19. Acid/Base ActivityIdentifying Conjugate Acid-Base Pairs PROBLEM:The following reactions are important environmental processes. Identify the conjugate acid-base pairs. (a) H 2 PO 4 - ( aq ) + CO 3 2- ( aq ) HPO 4 2- ( aq ) + HCO 3 - ( aq ) (b) H 2 O( l ) + SO 3 2- ( aq ) OH - ( aq ) + HSO 3 - ( aq )

20. Strengths of conjugate acid- base pairs

21. 3.18 HF

22. Equilibrium favors reaction of the stronger acid and stronger base to give the weaker acid and weaker base pKa 4.76 pKa 9.24

23. acetic acid + sodium bicarbonate (omit Na + ) 6.36 pK a = 4.76 CO 2 H2OH2O +

24. Acid/Base ActivityPredicting the K Acid-Base Reaction “Will this deprotonate that” PROBLEM:Predict the net direction and whether K a is greater or less than 1 for each of the following reactions (assume equal initial concentrations of all species): (b) H 2 O( l ) + HS - ( aq ) OH - ( aq ) + H 2 S( aq ) (a) H 2 PO 4 - ( aq ) + NH 3 ( aq ) HPO 4 2- ( aq ) + NH 4 + ( aq )

25. In Class a) You smell ammonia when NH 3 dissolves in water Use balanced equations showing the net direction of the reaction to describe each of the following observations. b) The odor goes away when you add an excess of HCl to the solution in part a) c) The odor returns when you add an excess of NaOH to the solution in part b)

26. Acid/Base ActivityFinding the K a of a Weak Acid from the pH of Its Solution PROBLEM:Phenylacetic acid (C 6 H 5 CH 2 COOH, simplified here as HPAc) builds up in the blood of persons with phenylketonuria, an inherited disorder that, if untreated, causes mental retardation and death. A study of the acid shows that the pH of 0.12M HPAc is 2.60. What is the K a of phenylacetic acid?

27. Acid/Base ActivityDetermining Concentrations from K a and Initial [HA] PROBLEM:Propanoic acid (CH 3 CH 2 COOH, which we simplify and HPr) is an organic acid whose salts are used to retard mold growth in foods. What is the [H 3 O + ] of 0.10M HPr (K a = 1.3x10 -5 )?

28. Percent HA dissociation = [HA] dissociated [HA] initial x 100 Polyprotic acids acids with more than more ionizable proton H 3 PO 4 ( aq ) + H 2 O( l ) H 2 PO 4 - ( aq ) + H 3 O + ( aq ) H 2 PO 4 - ( aq ) + H 2 O( l ) HPO 4 2- ( aq ) + H 3 O + ( aq ) HPO 4 2- ( aq ) + H 2 O( l ) PO 4 3- ( aq ) + H 3 O + ( aq ) K a1 = [H 3 O + ][H 2 PO 4 - ] [H 3 PO 4 ] K a2 = [H 3 O + ][HPO 4 2- ] [H 2 PO 4 - ] K a3 = [H 3 O + ][PO 4 3- ] [HPO 4 2- ] K a1 > K a2 > K a3 = 7.2x10 -3 = 6.3x10 -8 = 4.2x10 -13

29. ACID STRENGTH Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30. Acid/Base ActivityCalculating Equilibrium Concentrations for a Polyprotic Acid PROBLEM:Ascorbic acid (H 2 C 6 H 6 O 6 ; H 2 Asc for this problem), known as vitamin C, is a diprotic acid (K a1 = 1.0x10 -5 and K a2 = 5x10 -12 ) found in citrus fruit. Calculate [H 2 Asc], [HAsc - ], [Asc 2- ], and the pH of 0.050M H 2 Asc.

31. + CH 3 NH 3 + OH - methylammonium ion Abstraction of a proton from water by methylamine + CH 3 NH 2 H2OH2O methylamine Lone pair binds H +

32. BASE STRENGTH Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33. Acid/Base ActivityDetermining pH from K b and Initial [B] PROBLEM:Dimethylamine, (CH 3 ) 2 NH, a key intermediate in detergent manufacture, has a K b of 5.9x10 -4. What is the pH of 1.5M (CH 3 ) 2 NH?

34. Acid/Base ActivityDetermining the pH of a Solution of A - PROBLEM:Sodium acetate (CH 3 COONa, or NaAc for this problem) has applications in photographic development and textile dyeing. What is the pH of 0.25M NaAc? K a of acetic acid (HAc) is 1.8x10 -5.

35. The effect of atomic and molecular properties on nonmetal hydride acidity. 6A(16) H2OH2O H2SH2S H 2 Se H 2 Te 7A(17) HF HCl HBr HIHI Electronegativity increases, acidity increases Bond strength decreases, acidity increases

36. HO I HOBrHOCl << HO O O O << The relative strengths of oxoacids  HOCl  

37. Free IonHydrated IonKaKa Fe 3+ Sn 2+ Cr 3+ Al 3+ Be 2+ Cu 2+ Pb 2+ Zn 2+ Co 2+ Ni 2+ Fe(H 2 O) 6 3+ ( aq ) Sn(H 2 O) 6 2+ ( aq ) Cr(H 2 O) 6 3+ ( aq ) Al(H 2 O) 6 3+ ( aq ) Be(H 2 O) 4 2+ ( aq ) Cu(H 2 O) 6 2+ ( aq ) Pb(H 2 O) 6 2+ ( aq ) Zn(H 2 O) 6 2+ ( aq ) Co(H 2 O) 6 2+ ( aq ) Ni(H 2 O) 6 2+ ( aq ) 6 x 10 -3 4 x 10 -4 1 x 10 -4 1 x 10 -5 4 x 10 -6 3 x 10 -8 1 x 10 -9 2 x 10 -10 1 x 10 -10 ACID STRENGTH K a Values of Some Hydrated Metal Ions at 25 0 C Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

38. Al(H 2 O) 5 OH 2+ Al(H 2 O) 6 3+ The acidic behavior of the hydrated Al 3+ ion H2OH2O H3O+H3O+ Electron density drawn toward Al 3+ Nearby H 2 O acts as base

40. Acid/Base ActivityPredicting Relative Acidity of Salt Solutions PROBLEM:Predict whether aqueous solutions of the following are acidic, basic, or neutral, and write an equation for the reaction of any ion with water: (a) Potassium perchlorate, KClO 4 (b) Sodium benzoate, C 6 H 5 COONa (c) Chromium trichloride, CrCl 3 (d) Sodium hydrogen sulfate, NaHSO 4

41. Acid/Base ActivityPredicting the Relative Acidity of Salt Solutions from K a and K b of the Ions PROBLEM:Determine whether an aqueous solution of zinc formate, Zn(HCOO) 2, is acidic, basic, or neutral.

42. Molecular Structure and Acidity relative acidities the more A: (-) stable, greater the acidity of H-A Ways to stabilize A: (-) the negative charge ON a more electronegative atom ON larger atom RESONANCE delocalized STABILIZED by inductive effect IN an orbital with more s character

43. within a period - the greater the electronegativity of A: (-) the more A: (-) is stablized  the stronger the acid Conjugate base Acid Molecular Structure and Acidity pK a 38 pK a 16 pK a 51

44. Size of A: (-) Within a column - the larger the atom bearing the (-), the greater its stability Molecular Structure and Acidity

45. Resonance delocalized of charge in A - Compare alcohol and carboxylic acid acidity Molecular Structure and Acidity resonance stabilization

46. curved arrows show the flow of electrons in an acid-base reaction Molecular Structure and Acidity

47. molecules may have 2 or more sites that can accept a H + e.g. carboxylic acids, esters, and amides protonation favored where the charge is more delocalized which oxygen is protonated?

48. Molecular Structure and Acidity resonance octets greater contribution even with plus charge on O

49. Molecular Structure and Acidity H + on the hydroxyl can “write” contributing structures create & separate charge  H + on the carbonyl

50. Molecular Structure and Acidity Does proton transfer to an amide group occur preferentially on the amide oxygen or the amide nitrogen?

51. inductive effect, electron-withdrawing covalent bonds transmit electronegativity (polarizing) effects push or pull shared e (-) s of adjacent atoms Molecular Structure and Acidity decreases w/ distance

52. inductive effect: butanoic and chlorobutanoic acids Molecular Structure and Acidity

53. Hybridization greater the % s character with (-) the more stable the anion Molecular Structure and Acidity

54. Molecules as Lewis Acids acidbaseadduct An acid is an electron-pair acceptor. A base is an electron-pair donor. M 2+ H 2 O( l ) M(H 2 O) 4 2+ ( aq ) adduct