3. The Chemistry of Acids and Bases

4. Acid and Bases

7. Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Electrolytes (conduct electricity) þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

8. Some Common Acids Hydrochloric Acid Formula Name Common Use HCl aka Muriatic acid, Stomach acid Nitric Acid HNO 3 Strong Oxidizer Acetic Acid HC 2 H 3 O 2 Vinegar Sulfuric Acid H 2 SO 4 refinement of petroleum, fertilizers Citric Acid H3C6H5O7H3C6H5O7 Fruits and Candy Carbonic Acid H 2 CO 3 Pop and seawater

9. Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Electrolytes (conduct electricity)  Feel slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

10. Some Common Bases NaOH KOH Ba(OH) 2 Mg(OH) 2 Al(OH) 3 sodium hydroxidelye potassium hydroxideliquid soap barium hydroxidestabilizer for plastics magnesium hydroxide“MOM” Milk of magnesia aluminum hydroxideMaalox (antacid) Formula Name Common Name

11. SOME DEFINITIONS Amphoteric - A substance that can act as either an acid or a base, e.g., H 2 O, HCO 3 -Amphoteric - A substance that can act as either an acid or a base, e.g., H 2 O, HCO 3 - Polyprotic acid or base - An acid or base that can donate or accept, respectively, more than one proton, e.g., H 3 PO 4, H 2 CO 3, H 4 EDTAPolyprotic acid or base - An acid or base that can donate or accept, respectively, more than one proton, e.g., H 3 PO 4, H 2 CO 3, H 4 EDTA

12. Acid/Base Definitions  Arrhenius Model  Acids produce hydrogen ions in aqueous solutions  Bases produce hydroxide ions in aqueous solutions  Bronsted-Lowry Model  Acids are proton donors  Bases are proton acceptors  Lewis Acid Model  Acids are electron pair acceptors  Bases are electron pair donors

13. Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H + ions (or hydronium ions H 3 O + ) Bases – produce OH - ions (problem: some bases don’t have hydroxide ions!)

14. Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water NaOH + H 2 O  OH - + Na + + H 2 O

15. Definition #2: Brønsted–Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron! Acid & Base Definitions PDA (proton donated acid) BAD (Brønsted–Lowry acid donates)

16. Acid A Brønsted-Lowry Acid is a proton donor Base A Brønsted-Lowry Base is a proton acceptor AcidBase Conjugate Acid The Brønsted definition means NH 3 is a Base in water — and water is itself an Acid Conjugate Base ACID-BASE THEORIES

17. Conjugate Pairs Conjugate Acid – the remaining ion or molecule that can re-accept the proton and act as a base Conjugate Base – the species that is formed when a Brønsted-Lowry base gains a proton.

18. Acids & Base Definitions Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair Definition #3 – Lewis

19. Formation of hydronium ion is an excellent example. Lewis Acids & Bases Electron pair of the new O-H bond originates on the Lewis base.Electron pair of the new O-H bond originates on the Lewis base.

20. Acids & Base Definitions Summary

24. Acid Dissociation HA (aq) + H 2 O (l) +  H 3 O + (aq) + A - (aq) Acid base Conjugate Conjugate acid base Alternately, H + may be written in its hydrated form, H 3 O + (hydronium ion)

25. Acid Dissociation HA (aq) +  H + (aq) + A - (aq) Acid Proton Conjugate base Alternately, H + may be written in its hydrated form, H 3 O + (hydronium ion)

26. Dissociation of Strong Acids Strong acids are assumed to dissociate completely in solution. Large K a or small K a ? Reactant favored or product favored?

27. Dissociation Constants: Strong Acids AcidFormula Conjugate Base KaKa Perchloric HClO 4 ClO 4 - Very large Hydriodic HI I - Very large Hydrobromic HBr Br - Very large Hydrochloric HCl Cl - Very large Nitric HNO 3 NO 3 - Very large Sulfuric H 2 SO 4 HSO 4 - Very large

28. Dissociation of Weak Acids Weak acids are assumed to dissociate only slightly (less than 5%) in solution. Large K a or small K a ? Reactant favored or product favored?

29. Dissociation Constants: Weak Acids AcidFormula Conjugate Base KaKa Iodic HIO 3 IO 3 - 1.7 x 10 -1 Oxalic H 2 C 2 O 4 HC 2 O 4 - 5.9 x 10 -2 Sulfurous H 2 SO 3 HSO 3 - 1.5 x 10 -2 Phosphoric H 3 PO 4 H 2 PO 4 - 7.5 x 10 -3 Citric H 3 C 6 H 5 O 7 H 2 C 6 H 5 O 7 - 7.1 x 10 -4 Nitrous HNO 2 NO 2 - 4.6 x 10 -4 Hydrofluoric HF F - 3.5 x 10 -4 Formic HCOOH HCOO - 1.8 x 10 -4 Benzoic C 6 H 5 COOH C 6 H 5 COO - 6.5 x 10 -5 Acetic CH 3 COOH CH 3 COO - 1.8 x 10 -5 Carbonic H 2 CO 3 HCO 3 - 4.3 x 10 -7 Hypochlorous HClO ClO - 3.0 x 10 -8 Hydrocyanic HCN CN - 4.9 x 10 -10

30. Self-Ionization of Water H 2 O + H 2 O  H 3 O + + OH - At 25 , [H 3 O + ] = [OH - ] = 1 x 10 -7 K w is a constant at 25  C: K w = [H 3 O + ][OH - ] K w = (1 x 10 -7 )(1 x 10 -7 ) = 1 x 10 -14 = [K a ][K b ]

31. Calculating pH, pOH pH = -log 10 (H 3 O + ) pOH = -log 10 (OH - ) Relationship between pH and pOH pH + pOH = 14 Finding [H 3 O + ], [OH - ] from pH, pOH [H 3 O + ] = 10 -pH [OH - ] = 10 -pOH

32. pH and pOH Calculations

33. Do Problems: 29 43a&d

36. A Weak Acid Equilibrium Problem What is the pH of a 0.50 M solution of acetic acid, HC 2 H 3 O 2, K a = 1.8 x 10 -5 ? Step #1: Write the dissociation equation HC 2 H 3 O 2 (aq) + H 2 O (l)  C 2 H 3 O 2 - (aq) + H 3 O + (aq)

37. A Weak Acid Equilibrium Problem What is the pH of a 0.50 M solution of acetic acid, HC 2 H 3 O 2, K a = 1.8 x 10 -5 ? Step #2: ICE it! HC 2 H 3 O 2  C 2 H 3 O 2 - + H + I C E 0.50 0 ~0 - x +x 0.50 - x xx

38. A Weak Acid Equilibrium Problem What is the pH of a 0.50 M solution of acetic acid, HC 2 H 3 O 2, K a = 1.8 x 10 -5 ? Step #3: Set up the law of mass action HC 2 H 3 O 2  C 2 H 3 O 2 - + H + 0.50 - xxx E

39. A Weak Acid Equilibrium Problem What is the pH of a 0.50 M solution of acetic acid, HC 2 H 3 O 2, K a = 1.8 x 10 -5 ? Step #4: Solve for x, which is also [H + ] HC 2 H 3 O 2  C 2 H 3 O 2 - + H + 0.50 - xxx E [H + ] = 3.0 x 10 -3 M

40. A Weak Acid Equilibrium Problem What is the pH of a 0.50 M solution of acetic acid, HC 2 H 3 O 2, K a = 1.8 x 10 -5 ? Step #5: Convert [H + ] to pH HC 2 H 3 O 2  C 2 H 3 O 2 - + H + 0.50 - xxx E pH = - log (3.0 x 10 -3 ) = 2.52

41. Do Problem: 54

42. Do Problem: 55b

43. Do Problem: 55a

50. Dissociation of Strong Bases  Strong bases are metallic hydroxides  Group I hydroxides (most common in lab NaOH, KOH) are very soluble  Group II hydroxides (Ca, Ba, Sr) are less soluble  pH of strong bases is calculated directly from the concentration of the base in solution MOH(s)  M + (aq) + OH - (aq)

51. Reaction of Weak Bases with Water The base reacts with water, producing its conjugate acid and hydroxide ion: CH 3 NH 2 + H 2 O  CH 3 NH 3 + + OH - K b = 4.38 x 10 -4

52. K b for Some Common Weak Bases BaseFormula Conjugate Acid KbKb Ammonia NH 3 NH 4 + 1.8 x 10 -5 Methylamine CH 3 NH 2 CH 3 NH 3 + 4.38 x 10 -4 Ethylamine C 2 H 5 NH 2 C 2 H 5 NH 3 + 5.6 x 10 -4 Diethylamine (C 2 H 5 ) 2 NH (C 2 H 5 ) 2 NH 2 + 1.3 x 10 -3 Triethylamine (C 2 H 5 ) 3 N (C 2 H 5 ) 3 NH + 4.0 x 10 -4 Hydroxylamine HONH 2 HONH 3 + 1.1 x 10 -8 HydrazineH 2 NNH 2 H 2 NNH 3 + 3.0 x 10 -6 Aniline C 6 H 5 NH 2 C 6 H 5 NH 3 + 3.8 x 10 -10 Pyridine C 5 H 5 N C 5 H 5 NH + 1.7 x 10 -9 Many students struggle with identifying weak bases and their conjugate acids.What patterns do you see that may help you?

53. Reaction of Weak Bases with Water The generic reaction for a base reacting with water, producing its conjugate acid and hydroxide ion: B + H 2 O  BH + + OH -

54. A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? Step #1: Write the equation for the reaction NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

55. A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? Step #2: ICE it! I C E 0.50 0 0 - x +x 0.50 - x xx NH 3 + H 2 O  NH 4 + + OH -

56. A Weak Base Equilibrium Problem Step #3: Set up the law of mass action 0.50 - xxx E What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? NH 3 + H 2 O  NH 4 + + OH -

57. A Weak Base Equilibrium Problem Step #4: Solve for x, which is also [OH - ] 0.50 - xxx E [OH - ] = 3.0 x 10 -3 M NH 3 + H 2 O  NH 4 + + OH - What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ?

58. A Weak Base Equilibrium Problem Step #5: Convert [OH - ] to pH 0.50 - xxx E What is the pH of a 0.50 M solution of ammonia, NH 3, K b = 1.8 x 10 -5 ? NH 3 + H 2 O  NH 4 + + OH - pOH = - log (3.0 x 10 -3 ) = 2.52 pH = 14 - pOH = 11.48

59. Do Problem: 86

60. Do Problem: 87

64. Acid-Base Properties of Salts Type of SaltExamplesCommentpH of solution Cation is from a strong base, anion from a strong acid KCl, KNO 3 NaCl NaNO 3 Both ions are neutral Neutral These salts simply dissociate in water: KCl(s)  K + (aq) + Cl - (aq)

65. Acid-Base Properties of Salts Type of SaltExamplesCommentpH of solution Cation is from a strong base, anion from a weak acid NaC 2 H 3 O 2 KCN, NaF Cation is neutral, Anion is basic Basic C 2 H 3 O 2 - + H 2 O  HC 2 H 3 O 2 + OH- base acid acid base The basic anion can accept a proton from water:

66. Acid-Base Properties of Salts Type of SaltExamplesCommentpH of solution Cation is the conjugate acid of a weak base, anion is from a strong acid NH 4 Cl, NH 4 NO 3 Cation is acidic, Anion is neutral Acidic NH 4 + (aq)  NH 3 (aq) + H + (aq) Acid Conjugate Proton base The acidic cation can act as a proton donor:

67. Acid-Base Properties of Salts Type of SaltExamplesCommentpH of solution Cation is the conjugate acid of a weak base, anion is conjugate base of a weak acid NH 4 C 2 H 3 O 2 NH 4 CN Cation is acidic, Anion is basic See below  IF K a for the acidic ion is greater than K b for the basic ion, the solution is acidic  IF K b for the basic ion is greater than K a for the acidic ion, the solution is basic  IF K b for the basic ion is equal to K a for the acidic ion, the solution is neutral

69. Do Problem : 116

70. Strength of oxyacids The more oxygen hooked to the central atom, the more acidic the hydrogen. HClO 4 > HClO 3 > HClO 2 > HClO Remember that the H is attached to an oxygen atom. The oxygens are electronegative Pull electrons away from hydrogen

71. Strength of oxyacids Electron Density ClOH

72. Strength of oxyacids Electron Density ClOHO

73. Strength of oxyacids ClOH O O Electron Density

74. Strength of oxyacids ClOH O O O Electron Density

75. Acid-Base Properties of Salts Type of SaltExamplesCommentpH of solution Cation is a highly charged metal ion; Anion is from strong acid Al(NO 3 ) 2 FeCl 3 Hydrated cation acts as an acid; Anion is neutral Acidic Step #1: AlCl 3 (s) + 6H 2 O  Al(H 2 O) 6 3+ (aq) + Cl - (aq) Salt water Complex ion anion Step #2: Al(H 2 O) 6 3+ (aq)  Al(OH)(H 2 O) 5 2+ (aq) + H + (aq) Acid Conjugate base Proton

76. Effect of Structure on Acid-Base Properties

77. Hydrated metals Highly charged metal ions pull the electrons of surrounding water molecules toward them. Make it easier for H + to come off. Al +3 O H H

78. Acid-Base Properties of Oxides Non-metal oxides dissolved in water can make acids. SO 3 (g) + H 2 O(l) H 2 SO 4 (aq) Ionic oxides dissolve in water to produce bases. CaO(s) + H 2 O(l) Ca(OH) 2 (aq)

80. What is the concentration of H 3 O + in pure water? 1.1.00 x 10 –7 M 2.7.00 M 3.1.00 x 10 -14 4.1.00 x 10 7 M 5.7.00 x 10 -14 Response Counter

81. [H + ] = 8.26 x 10 –5 M, what is the pH of the solution? 1.2.16 2.4.1 3.4.08 4.4.083 5.8.024 Response Counter

82. Which of the following is a conjugate acid/base pair? 1.HCl/OCl - 2.H 2 SO 4 /SO 4 2 - 3.NH 4 + /NH 3 4.H 3 O + /OH - 5.none of these Response Counter

83. Which of the following indicates the most basic solution? 1.[H + ] = 1 × 10 –10 M 2.pOH =6.7 3.[OH – ] = 7 × 10 –5 M 4.pH = 4.2 5.At least two of the solutions are equally basic. Response Counter

84. Dissolving Na 2 SO 4 in water will create a ______ solution. 1.Acidic 2.Basic 3.Neutral 4.Cannot be determined. Response Counter

85. Calculate the pH of a 0.17 M solution of HOCl, K a = 3.5 10 -8. 1.4.11 2.8.23 3.9.89 4.1.00 5.3.77 Response Counter