Chapter 10 Acids and Bases

1. Chapter 10 Acids and Bases 10.1 Acids and Bases 10.2 Conjugate Acid-Base Pairs 10.3 Strengths of Acids and Bases 10.4 Dissociation Constants 10.5 Ionization of Water 10.6 The pH Scale 10.7 Reactions of Acids and Bases (just neutralization reactions) 10.9 Buffers

2. 10.1 Acids • Arrhenius acids • Produce H+ ions in water. H2OHCl H+(aq) + Cl– (aq) • Are electrolytes. • Have a sour taste. • Corrode metals. • React with bases to form salts and water. • Examples: • Vinegar (5% acetic acid) • Citric acid (fruits) • Ascorbic acid (vitamin C) • Lactic acid (in muscles) • Phosphoric acid (Coke)

3. Bases • Arrhenius bases • Produce OH– ions in water. • Taste bitter or chalky. • Are electrolytes. • Feel soapy and slippery. • React with acids to form salts and water. • Examples: • Draino (NaOH) • Baking Soda (NaHCO3) • Bleach (NaOCl) • Ammonia (NH3) • Antacid

4. Comparing Acids and Bases

5. Learning Check Identify each as a characteristic of an A) acid or B) base ____1. Has a sour taste. ____2. Produces OH- in aqueous solutions. ____3. Has a chalky taste. ____4. Is an electrolyte. ____5. Produces H+ in aqueous solutions.

6. Solution Identify each as a characteristic of an A) acid or B) base A 1. Has a sour taste. B 2. Produces OH– in aqueous solutions. B 3. Has a chalky taste. A, B4. Is an electrolyte. A 5. Produces H+ in aqueous solutions.

7. Names of Acids • Acids with H and one nonmetal are named with the prefix hydro- and end with -ic acid.HCl hydrochloric acid • Acids with H and a polyatomic ion are named by changing the end of an –ate ion to -ic acid and an –ite ion to -ous acid. HClO3 chloric acid HClO2 chlorous acid

8. Some Acids and Their Anions

9. Learning Check Name each of the following as acids: A. HBr 1. bromic acid 2. bromous acid 3. hydrobromic acid B. H2CO3 1. carbonic acid 2. hydrocarbonic acid 3. carbonous acid

10. Solution A. HBr 3. hydrobromic acid The name of an acid with H and one nonmetal begins with the prefix hydro- and ends with -ic acid. B.H2CO3 1. carbonic acid An acid with H and a polyatomic ion is named by changing the end of an –ate ion to -ic acid.

11. Some Common Bases • Bases with OH- ions are named as the hydroxide of the metal in the formula. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH)2 barium hydroxide Al(OH)3 aluminum hydroxide Fe(OH)3 iron (III) hydroxide

12. Learning Check Match the formulas with the names: A. ___ HNO2 1) hydrochloric acid B. ___Ca(OH)2 2) sulfuric acid C. ___H2SO4 3) sodium hydroxide D. ___HCl 4) nitrous acid E. ___NaOH 5) calcium hydroxide

13. Solution Match the formulas with the names: A. 4 HNO24) nitrous acid B. 5 Ca(OH)2 5) calcium hydroxide C. 2 H2SO4 2) sulfuric acid D.1 HCl 1)hydrochloric acid E. 3 NaOH 3) sodium hydroxide

14. Johannes BrØnsted and Thomas Lowry (1923) According to the Brønsted-Lowry theory, • Acids are hydrogen ion (H+) donors. • Bases are hydrogen ion (H+) acceptors. donor acceptor hydronium ion HCl + H2O H3O+ + Cl- + - + +

15. NH3, A Bronsted-Lowry Base • When NH3 dissolves in water, a few NH3 molecules react with water to form ammonium ion NH4+ and a hydroxide ion. NH3 + H2O NH4+(aq) + OH- (aq) acceptor donor +- + +

16. 10.2 Conjugate Acids and Bases • An acid that donates H+ forms a conjugate base. • A base that accepts a H+ forms a conjugate acid. • In an acid-base reaction, there are two conjugate acid-base pairs. acid 1 conjugate base 1 + + base 2 conjugate acid 2 HF H3O+ F- H2O

17. Conjugate Acid-Base Pairs • A conjugate acid-base pair is two substances related by a loss or gain of H+. + + acid 1– conjugate base 1 base 2– conjugate acid 2 HF H3O+ F- H2O HF, F- H2O, H3O+

18. Learning Check A. Write the conjugate base of the following: 1. HBr 2. H2S 3. H2CO3 B. Write the conjugate acid of the following: 1. NO2– 2. NH3 3. OH–

19. Solution A. Write the conjugate base of the following: 1. HBr Br- 2. H2S HS– 3. H2CO3 HCO3– B. Write the conjugate acid of the following: 1. NO2– HNO2 2. NH3 NH4+ 3. OH– H2O

20. Learning Check Identify the following that are acid-base conjugate pairs. 1. HNO2, NO2– 2. H2CO3, CO32 – 3. HCl, ClO4 – 4. HS–, H2S 5. NH3, NH4+

21. Solution Identify the following that are acid-base conjugate pairs. 1. HNO2, NO2– 4. HS–, H2S 5. NH3, NH4+

22. Learning Check A. The conjugate base of HCO3– is 1. CO32– 2. HCO3– 3. H2CO3 B. The conjugate acid of HCO3– is 1. CO32– 2. HCO3– 3. H2CO3 C. The conjugate base of H2O is 1. OH– 2. H2O 3. H3O+ D. The conjugate acid of H2O is 1. OH– 2. H2O 3. H3O+

23. Solution A. The conjugate base of HCO3 – is 1. CO32– B. The conjugate acid of HCO3– is 3. H2CO3 C. The conjugate base of H2O is 1. OH– D. The conjugate acid of H2O is 3. H3O+

24. 10.3 Strengths of Acids and Bases • Strong acids completely ionize (100%) in aqueous solutions.HCl + H2O H3O+ (aq) + Cl– (aq) (100 % ions) • Strong bases completely (100%) dissociate into ions in aqueous solutions. H2ONaOH Na+ (aq) + OH–(aq)(100 % ions)

25. Strong and Weak Acids • In an HCl solution, the strong acid HCl dissociates 100%. • A solution of the weak acid CH3COOH contains mostly molecules and a few ions.

26. Strong Acids • Only a few acids are strong acids. • The conjugate bases of strong acids are weak bases.

27. Weak Acids • Most acids are weak acids. The conjugate bases of weak acids are strong bases.

28. Strong Bases • Most bases in Groups 1A and 2A are strong bases. They includeLiOH, NaOH, KOH, and Ca(OH)2 • Most other bases are weak bases.

29. Learning Check Identify each of the following as a strong or weak acid or base. A. HBr B. HNO2 C. NaOH D. H2SO4 E. Cu(OH)2

30. Solution Identify each of the following as a strong or weak acid or base. A. HBr strong acid B. HNO2 weak acid C. NaOH strong base D. H2SO4 strong acid E. Cu(OH)2 weak base

31. Learning Check A. Identify the stronger acid in each pair. 1. HNO2 or H2S 2. HCO3– or HBr 3. H3PO4 or H3O+ B. Identify the strong base in each pair. 1. NO3– or F- 2. CO32– or NO2– 3. OH– or H2O

32. Solution A. Identify the stronger acid in each pair. 1. HNO2 2. HBr 3. H3O+ B. Identify the stronger base in each pair. 1. F- 2. CO32– 3. OH–

33. Equilibrium H2SO4 + H2O H3O+ + HSO4- stronger stronger weaker weaker acid base acid base CO3- + H2O HCO3- + OH- weaker weaker stronger stronger base acid acid base

34. 10.4 Strong Acids • In water, the dissolved molecules of a strong acid are essentially all separated into ions. • The concentrations of H3O+ and the anion (A–) are large.

35. Weak Acids In weak acids, • The equilibrium favors the undissociated (molecular) form of the acid. • The concentrations of the H3O+ and the anion (A–) are small.

36. Dissociation Constants • In a weak acid, the rate of the dissociation of the acid is equal to the rate of the association. HA + H2O H3O+ + A– • The equilibrium expression for a weak acid is Keq = [H3O+][A-] [HA][H2O]

37. Acid Dissociation Constants (Ka) • The [H2O] is large and remains unchanged. It is combined with the Keq to write the acid dissociation constant, Ka. Ka = Keq[H2O] = [H3O+][A-] [HA]

38. Writing Ka for a Weak Acid Write the Ka for H2S. 1. Write the equation for the dissociation of H2S. H2S + H2O H3O+ + HS– 2. Set up the Ka expression Ka = [H3O+][HS-] [H2S]

39. Learning Check Write the Ka for HCN.

40. Solution Write the Ka for HCN. Write the equation for the dissociation of HCN. HCN + H2O H3O+ + CN– Set up the Ka expression Ka = [H3O+][CN–] [HCN] Note: Ka = Keq [H2O]

41. Acid dissociation constants Larger Ka (stronger acid) Larger Kb (stronger base) Smaller Ka (weaker acid) Smaller Kb (weaker base)

42. 10.5 Ionization of Water • In water, H+ is transferred from one H2O molecule to another. • One water molecule acts as an acid, while another acts as a base (amphiprotic).H2O + H2O H3O+ + OH – .. .. .. .. :O: H + :O:H H:O:H + + :O:H– .. .. .. .. HH H water molecules hydronium hydroxide ion (+)ion (–)

43. Pure Water is Neutral • In pure water, the ionization of molecules produces small, but equal quantities of H3O+ and OH- ions.H2O + H2O H3O+ + OH- • Molar concentrations are indicated as [H3O+] and [OH-].[H3O+] = 1.0 x 10-7 M[OH-] =1.0 x 10-7 M

44. Acidic Solutions • Adding an acid to pure water increases the [H3O+]. • In acids, [H3O+] exceeds 1.0 x 10–7 M. • As [H3O+] increases, [OH–] decreases.

45. Basic Solutions • Adding a base to pure water increases the [OH–]. • In bases, [OH–] exceeds 1.0 x 10–7M. • As [OH–] increases, [H3O+] decreases.

46. Comparison of [H3O+] and [OH–]

47. Ion Product of Water, Kw • The ion product constant, Kw, for water is the product of the concentrations of the hydronium and hydroxide ions. Kw = [H3O+][OH–] • We can obtain the value of Kw using the concentrations in pure water. Kw = [1.0 x 10–7][1.0 x 10–7] = 1.0 x 10–14

48. Kw in Acids and Bases • In neutral, acidic, and basic solutions, the Kw is equal to 1.0 x 10–14.

49. Calculating [H3O+] What is the [H3O+] of a solution if [OH–] is 1.0 x 10-8M? Rearrange the Kw expression for [H3O+ ]. Kw = [H3O+][OH–] = 1.0 x 10-14 [H3O+] = 1.0 x 10-14 [OH–] [H3O+] = 1.0 x 10-14 = 1.0 x 10-6 M 1.0 x 10- 8

50. Learning Check The [H3O+] of lemon juice is 1.0 x 10–3 M. What is the [OH–] of the solution? 1) 1.0 x 103 M 2) 1.0 x 10–11 M 3) 1.0 x 1011 M