1. Chapter 16

2. Overview: Definitions Arrhenius Bronsted -- Conjugate Pairs Hydronium Ion Relative Strengths Strong/Weak acids and reactions Strong/Weak bases and reactions K a ’s and K b ’s

3. pH and H 2 O Ionization Calculating Equilibrium Concentrations Hydrolysis Acidic and Basic Salts Polyprotic Acids Molecular Structure/Bonding Lewis Acids and Bases

4. Acids sour corrosive reddens blue vegetable colors react with bases Bases bitter soapy restores vegetable colors reddened by acids react with acids

5. Arrhenius Acid: substance that releases or produces H + HCl (aq)  H + (aq) + Cl - (aq) Arrhenius Base: substance that releases or produces OH - NaOH (aq)  Na + (aq) + OH - (aq) Bronsted Acid: substance that donates a H + to another HNO 3(aq) + H 2 O (l)  H 3 O + (aq) + NO 3 - (aq) Bronsted Base: substance that accepts a H + from another CO 3 2- (aq) + H 2 O (l)  HCO 3 - (aq) + OH - (aq)

6. Water Dissociation: 2H 2 O H 3 O + + OH - Hydronium Ion -- because bare protons are unlikely H + transfer HO H HO H HO H HO H + ++  - - +

9. pH and Water Ionization: 2H 2 O ( l ) H 3 O + (aq) + OH - (aq) K w = [H 3 O + ][OH - ] = 1.0 x 10 -14 Reactant Favored ion-product constant for water (at 25  C) K = [H 3 O + ][OH - ] = K [H 2 O] 2 = [H 3 O + ][OH - ] [H 2 O] 2

10. pH = - log [H + ] = - log [H 3 O + ] neutral solution: [H 3 O + ] = [OH - ] 2H 2 O H 3 O + + OH - 1.0 x 10 -14 = [H 3 O + ][OH - ] = [H 3 O + ] 2 [H 3 O + ] = 1.0 x 10 -7 M pH = - log (1.0 x 10 -7 ) = 7.0

11. non-neutral solutions: [H + ] > [OH - ] acidic solutions: pH < 7.0 basic solutions: [H + ] < [OH - ] pH > 7.0

12. pH of Strong Acid and Base Solutions: Calculate the pH of a solution containing 0.00100 M of a strong acid such as HCl. HCl (aq) H + (aq) + OH - (aq) 0.00100 0.00100 0.00100 pH = - log (0.00100) = 3.00 but....

13. What about H 3 O + from water? 2 H 2 O H 3 O + + OH - initial0.00100 0 change +x +x equil. 0.00100 + x x 1 x 10 -14 = (0.00100 + x)(x) x = H 3 O + and OH - from disso. of water

14. [H 3 O + ] (1.0 x 10 -11 ) = 1.0 x 10 -14 [H 3 O + ] = 1.0 x 10 -3 M pH = 3.0 1 x 10 -14 = (0.00100 + x)(x) x = 1.00 x 10 -11 M = [OH - ] K w = [H 3 O + ] [OH - ] 0 x is very small compared to 0.00100 & can be neglected [H + ]  [H 3 O + ] the conc. of H + in a solution of a strong acid is the conc. of the strong acid pOH = 11.0 Note: pH + pOH = 14.0

15. Bottom Line:  [H + ] = [H 3 O + ] = [H 5 O 2 + ] = [H 9 O 4 + ] hydrated hydrogen ions  neutral solution [H 3 O + ] = [OH - ] pH = 7  acidic solution [H 3 O + ] > [OH - ] pH < 7  basic solution [H 3 O + ] 7  the concentration of [H 3 O + ] in a strong acid is the concentration of the acid

16. Calculate the pH of a solution containing 0.010 M KOH. KOH  K + (aq) + OH - (aq) 0.010 M 0.010 M 0.010 M 1.0 x 10 -14 = [H + ] (0.010 M) [H + ] = 1.0 x 10 -12 M pH = 12.0 strong base, complete rxn, stoichiometric contribution of [H + ] from dissociation of H 2 O is negligible

17. Calculate the [H + ] and [OH - ] in a solution that has a pH = 8.60 - log [H + ] = pH - log [H + ] = 8.60 log [H + ] = -8.60 [H + ] = anti log (-8.60) [H + ] = 1.8 x 10 -4 M [OH - ] = 5.6 x 10 -11 M

18. Basic Neutral Acidic pH [H 3 O + ] [OH - ] pOH 7.0 10 -7 10 -7 7.0 14 10 -14 1 0 0 1 10 -14 14 vinegar, cola milk ammonia human blood

19. Measuring pH:  pH meter -- electrodes measure pH –most precise method  acid-base indicators –less precise but good when a pH meter is not available –substances which are differently colored at different pH values –litmus, phenolphthalein, thymol blue

21. Arrhenius Acid: substance that releases or produces H + HCl (aq)  H + (aq) + Cl - (aq) Arrhenius Base: substance that releases or produces OH - NaOH (aq)  Na + (aq) + OH - (aq) Bronsted Acid: substance that donates a H + to another HNO 3(aq) + H 2 O (l)  H 3 O + (aq) + NO 3 - (aq) Bronsted Base: substance that accepts a H + from another CO 3 2- (aq) + H 2 O (l)  HCO 3 - (aq) + OH - (aq)

22. Examples: NH 4 + (aq) + H 2 O ( l )  H 3 O + (aq) + NH 3(aq) acidbase conjugate acid conjugate base PO 4 3- (aq) + H 2 O ( l )  HPO 4 2- (aq) + OH - (aq) H+H+ base acid conjugate acid conjugate base H+H+ conjugate pair

23. HCO 3 - (aq) + H 2 O ( l )  H 3 O + (aq) + CO 3 2- (aq) HCO 3 - (aq) + H 2 O ( l )  H 2 CO 3(aq) + OH - (aq) Some species can act as an acid or base: acidbase conjugate acid conjugate base base acid conjugate acid conjugate base HCO 3 - is an amphiprotic substance H+H+ H+H+

24. You Must Know: Hwhat an acid and a base is and how to identify both know definitions and properties Hthe reaction of an acid and a base with water Hhow to identify acid, base, conjugate acid and conjugate base Hwhat the hydronium ion is and the ionization reaction of water

25. Problems: HX + H 2 O  H 3 O + + X - A B CA CB What is the conjugate base of: H 2 S NH 4 + NH 3 H 2 O OH - HS - NH 3 NH 2 - OH - O 2- What is the conjugate acid of: NO 3 - HPO 4 2- H 2 SO 4 HNO 3 H 2 PO 4 - H 3 SO 4 +

26. Relative Strengths: HCl + H 2 O H 3 O + + Cl - equilibrium is a competition between the bases H 2 O and Cl - -- the equilibrium will lie toward the direction of the weaker acid and base in this case, H 2 O is a stronger base than Cl - as it competes much more effectively for the H + stronger Bweaker Bstronger Aweaker A

27. HCN + H 2 O H 3 O + + CN - H 2 O < CN - weaker Bweaker Astronger Astronger B

28. Which is the weaker acid: H 2 S + CN - HCN + HS - HCO 3 - + SO 4 2- HSO 4 - + CO 3 2- HClO 4 + H 2 O H 3 O + + ClO 4 - NH 4 + + H 2 O H 3 O + + NH 3 HCN HCO 3 - H3O+H3O+ NH 4 +

29. The stronger the acid the weaker its conjugate base: strongest acid weakest acid strongest conjugate base weakest conjugate base

31. Given the following, which is the weaker conjugate: HCl > CH 3 CO 2 H HCN < H 3 PO 4 H 2 SO 4 > H 2 SO 3 NH 3 > H 2 O HSO 4 - < CO 3 2- H - > NH 3 acids bases Cl - CH 3 CO 2 - < CN - H 2 PO 4 - > HSO 4 - HSO 3 - < NH 4 + H3O+H3O+ < H 2 SO 4 HCO 3 - > H2H2 NH 4 + <

32. Predicting Direction of Acid/Base Rxns. CH 3 CO 2 H + CN - HCN + CH 3 CO 2 - stronger Aweaker A weaker B stronger B

33. HSO 4 - + NH 3 NH 4 + + SO 4 2- stronger Aweaker A stronger Bweaker B

34. Strong Acids and Bases Strong Acids HCl HNO 3 HClO 4 HClO 3 H 2 SO 4 HBr HI Strong Bases Grp I hydroxides Grp II hydroxides (except Be) HX + H 2 O H 3 O + + X - MOH M + + OH - essentially complete rxns.

35. Weak Acids and Bases: HX + H 2 O H 3 O + + X - B + H 2 O BH + + OH - K a = [H 3 O + ][X - ] [HX] K b = [BH + ][OH - ] [B] < 1

36. Weak Acids Can Be: cations NH 4 + or [Cu(H 2 O) 6 ] 2+ anions H 2 PO 4 - or HCO 3 - neutral CH 3 CO 2 H or HCO 2 H Weak Bases Can Be: anions CO 3 2- or CN - neutral NH 3 or (CH 3 ) 3 N

37. You Must: HBe able to determine direction of rxn based on acid or base relative strengths HKnow the strong acids and strong bases HBe able to recognize weak acids and bases HKnow water ionization rxn, constant and expression HKnow what pH is and how to calculate it HKnow how to calculate equil. conc., pH, pOH for weak acids and bases

38. Problem 1 : A 0.015 M solution of an unknown base has a pH of 10.09. Is it a strong or weak base? What is the K b, if it is weak? Problem 2 : What are the equil. conc. of H 3 O +, acetate ion, acetic acid in a 0.20 M aqueous solution of acetic acid, CH 3 CO 2 H? Use the approximation whenever possible: When the initial weak acid/base conc. > 100  a/b neglect x when it is added to or subtracted from the initial conc.

39. If this were a strong base then [OH - ] = 0.015 M and pOH = 1.8 and pH = 12.2. pH = 10.09 and pOH = 3. 91  [OH - ] = 1.2 x 10 -4 K b = [HB + ][OH - ] = (1.2 x 10 -4 ) 2 [B] (0.015) B + H 2 O HB + + OH - = 9.6 x 10 -7 Answer 1:

40. CH 3 CO 2 H + H 2 O H 3 O + + CH 3 CO 2 - initial 0.20 0 0 change -x+x +x equil. 0.20 -x x x K a = 1.8 x 10 -5 = [H 3 O + ][CH 3 CO 2 - ] [CH 3 CO 2 H] K a = 1.8 x 10 -5 = (x)(x) x 2 = 3.6 x 10 -6 (0.20 -x) x = 1.9 x 10 -3 [CH 3 CO 2 - ]=[H 3 O + ] = 1.9 x 10 -3 M [CH 3 CO 2 H] = 0.20 M [CH 3 CO 2 - ]=[H 3 O + ] = 1.9 x 10 -3 M [CH 3 CO 2 H] = 0.20 M pH = 2.7 Answer 2:

41. What is the percent ionization? % ion = [H 3 O + ] x 100 [CH 3 CO 2 H] = 0.95 %

42. Polyprotic Acids and Bases: H 3 PO 4 + H 2 O H 3 O + + H 2 PO 4 - K a1 H 2 PO 4 - + H 2 O H 3 O + + HPO 4 2- K a2 HPO 4 2- + H 2 O H 3 O + + PO 4 3- K a3 H 3 PO 4 + 3H 2 O 3H 3 O + + PO 4 3-- (7.5 x 10 -3 )(6.2 x 10 -8 )(3.6 x 10 -13 ) = 1.7 x 10 -22 K a tot = K a1 K a2 K a3

43. Weak Bases:  Can be anions such as: – CN -, HSO 3 -, SO 3 2-, HCO 3 -, CO 3 2-, etc.  Can be N-containing compounds, such as: – NH 3, (CH 3 )NH 2, (CH 3 ) 2 NH, (CH 3 ) 3 N, etc.  React with water –B - + H 2 O HB + OH - or –B + H 2 O HB + + OH -  Have base dissociation constants, K b

44. NH 3 + H 2 O NH 4 + + OH - initial 0.20 M 0 0 change -x+x +x equil. 0.20 -x x x K b = 1.8 x 10 -5 = [NH 4 + ][OH - ] [NH 3 ] K b = 1.8 x 10 -5 = (x)(x) x 2 = 3.6 x 10 -6 (0.20 -x) x = 1.9 x 10 -3 [NH 4 + ]=[OH - ] = 1.9 x 10 -3 M [NH 3 ] = 0.20 M [NH 4 + ]=[OH - ] = 1.9 x 10 -3 M [NH 3 ] = 0.20 M pOH = 2.7 pH = 12.3 pOH = 2.7 pH = 12.3 Example:

45. CO 3 -2 + H 2 O OH - + HCO 3 -- K b1 HCO 3 -- + H 2 O OH - + H 2 CO 3 K b2 CO 3 + 2H 2 O 2OH -- + H 2 CO 3 2-- K b tot = K b1 K b2 (2.1 x 10 -4 )(2.4 x 10 -8 ) = 5.0 x 10 -12

46. Relationship of an acid K a and the K b of its conjugate base: NH 3 + H 2 O NH 4 + + OH - K b = 1.8 x 10 -5 NH 4 + + H 2 O NH 3 + H 3 O + K a = 5.6 x 10 -10 2H 2 O H 3 O + + OH - K w = 1 x 10 -14 For Conjugate Acid/Base Pairs: K b K a = K w or pK b  pK a = pK w conjugate pair rxns with water

47. Find K a for the conjugate acids of the following bases: K a = K w /K b NH 3 1.8 x 10 -5 C 5 H 5 N 1.7 x 10 -9 HS - 1.8 x 10 -7 CO 3 2- 1.8 x 10 -4 BaseK b Conj. AcidK a NH 4 + 5.6 x 10 -10 C 5 H 5 NH + 5.9 x 10 -6 H2SH2S 5.6 x 10 -8 5.6 x 10 -11 HCO 3 -

48. Acid/Base Hydrolysis Many salts produce solutions that are acidic or basic Why? because either (or both) the cation or anion of the salt acted as a weak acid or a weak base HX + H 2 O H 3 O + + X - or B + H 2 O BH + + OH - weak acid weak base

49. Which cations will not hydrolyze? Cations of strong bases -- Grp I and II (except Be) Li + Na + K + Rb + Cs + Mg 2+ Ca 2+ Sr 2+ Ba 2+ Anions of strong acids -- ClO 4 - ClO 3 - SO 4 2- NO 3 - Cl - Br - I - All other cations and anions will hydrolyze

50. Which cations will hydrolyze? Conjugate acids of weak bases: NH 4 + Al 3+ Cu 2+ etc. Conjugate bases of weak acids: CO 3 2 - CH 3 CO 2 - NH 3 F - etc.

51. What is the pH of the following salt solutions? NaCl NaF NH 4 Cl Na 2 CO 3 Cr(NO 3 ) 3 KNO 3 NaC 3 H 2 O 4 NH 4 CH 3 CO 2 Na + -- neutralCl - -- neutral Na + -- neutralF - -- basic NH 4 + -- acidicCl - -- neutral Na + -- neutralCO 3 2- -- basic Cr 3+ -- acidicNO 3 - -- neutral K + -- neutralNO 3 + -- neutral Na + -- neutralC 3 H 2 O 4 - -- basic NH 4 + -- acidicCH 3 CO 2 - -- basic N B A B A N B ?

52. Is NH 4 CH 3 CO 2 acidic or basic? NH 4 + + H 2 O H 3 O + + NH 3 K a = 5.6 x 10 -10 CH 3 CO 2 - + H 2 O CH 3 CO 2 H + OH - K b = 5.6 x 10 -10 weak acid & weak base strength equal -- neutral soln.

53. You Must: H Know what hydrolysis is H Know which cations hydrolyze or produce acidic solutions H Know which anions hydrolyze or produce basic solutions H Be able to estimate and calculate the pH of a salt solution H Know how to determine K a ’s & K b ’s of conjugate pairs

54. Strength of Acids: Can be increased by anything that facilitates the loss of a Proton (H + ) Bond Strength Polarity or  electronegativity Central Atom Charge or Oxidation #

55. Examples: IVA VA VIAVIIA row 2 CH 4 NH 3 H 2 O HF row 3 SiH 4 PH 3 H 2 S HCl Increasing acid strength

56. HClO 4 HClO 3 HClO 2 HClO Increasing acid strength AcidCl ox. # +7 +5 +3 +1 KaKa strong 1.1 x 10 -2 3.0 x 10 -8

57. HClO HBrO HIO Increasing acid strength AcidKaKa 3 x 10 -8 2.5 x 10 -9 2.3 x 10 -11

59. Organic Acids: C C O-O- O H H H C C O O-O- H H H Acetate ion resonance

60. C C OH O H H H Trifluoroacetic Acid K a = 5.0 x 10 -1 C C OH O F F F Acetic Acid K a = 1.8 x 10 -5

61. Lewis Acids and Bases: Lewis Acid -- accepts a pair of electrons Lewis Base -- donates a pair of electrons formation of a coordinate covalent bond N H H H B F F F

62. N H H H H+H+ NH 4 + NH 3 + H + Lewis Base -- donates a pair of electrons Lewis Acid -- accepts a pair of electrons