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Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION by Steven S. Zumdahl University of Illinois.

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Presentation on theme: "Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION by Steven S. Zumdahl University of Illinois."— Presentation transcript:

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2 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION by Steven S. Zumdahl University of Illinois

3 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Chemistry FIFTH EDITION Chapter 14 Acids and Bases

4 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Percent Dissociation (Ionization)

5 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Lets Do Problem 63 Note: For solutions of any weak acid HA, [H + ] decreases as [HA] 0 decreases; BUT The Percent Dissociation increases as [HA] 0 decreases. For a given weak acid, the percent dissociation Increases as the acid becomes more dilute.

6 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Figure The Effect of Dilution on the Percent Dissociation and (H+) of a Weak Acid Solution

7 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Calculating K a from Percent Dissociation of a Weak Acid See Sample Exercise page 643 Lets Do Problem #65

8 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Section 14.6 Bases Arrhenius Base: Substance that produces OH - ions in aqueous solution. Bronsted-Lowry Base: A proton acceptor Basic Solution: pH > 7

9 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Section 14.6 Bases Strong and weak are used in the same sense for bases as for acids. strong = complete dissociation (hydroxide ion supplied to solution) NaOH(s) Na + (aq) + OH (aq)

10 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Strong Bases Group 1A Hydroxides NaOH KOH LiOH RbOH CsOH Group 2A Hydroxides Ca(OH) 2 Ba(OH) 2 Sr(OH) 2

11 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Strong Bases Group 1A Hydroxides NaOH KOH LiOH very expensive RbOH very expensive CsOH very expensive Group 2A Hydroxides Ca(OH) 2 Ba(OH) 2 Sr(OH) 2

12 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Calculating the pH of Strong Base Solutions Assume 100 % Dissociation pH dominated by OH - from the dissociation. Lets do #77, together!!! Important & Interesting Information about Bases READ Section 14.6!

13 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 A base does not have to contain hydroxide ion. Many are proton acceptors & They increase the hydroxide ion concentration because of their reaction with water. NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) base acid

14 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 These bases typically have at least one unshared pair of electrons that is capable of forming a bond with a proton. Examples given on page 646. Bases have a lone pair of electrons located on a nitrogen atom.

15 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Substituted Ammonia Molecules Amines General Formula R x N(H) 3-x Read Chemical Impact on page 648.

16 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Bases (continued) weak = very little dissociation (or reaction with water) H 3 CNH 2 (aq) + H 2 O(l) H 3 CNH 3 + (aq) + OH (aq)

17 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Base Dissociation Constant (K b ) B (aq) + H 2 O(l) BH + (aq) + OH - (aq) K b = [BH + ]_[OH - ] [B] These types of Bases are Weak Bases. K b tend to be small.

18 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Lets do # 83, 85a, 89b & 91 together!!! Calculate the pH of solutions of Weak Bases Table of K b found in Table 14.3 on page 647 and in Appendix.

19 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Section 14.7 Polyprotic Acids... can furnish more than one proton (H + ) to the solution.

20 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 All polyprotic acids dissociate in a stepwise Manner -= i.e., one proton at a time. Each step has its own equilibrium constant. For a typical weak polyprotic acid K a1 > K a2 > K a3 i.e., each step of dissociation is successively weaker.

21 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 As protons are lost from polyprotic acids, a negative charge on the acid increases. It becomes more difficult to remove a positively charged proton from a negatively charged species.

22 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Lets look at Examples on page 650 H 2 CO 3 · H 3 PO 4 See Table 14.4 on page 651 for Stepwise Dissociation Constants for Common Polyprotic Acids.

23 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 For a typical Polyprotic acid in water, ONLY the 1 st dissociation step is Important in determining the pH. Therefore, the pH calculation of a weak polyprotic acid is identical to a weak monoprotic acid. Lets do Problem # 95. Homework: Extra Problem -Do #96

24 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 WHAT ABOUT SULFURIC ACID? Sulfuric acid is unique: (1) It is a strong acid in its 1 st dissociation step. H 2 SO 4 H + (aq) + HSO 4 - (aq) K a1 = (2) It is a weak acid in its second step. HSO 4 - (aq) H + (aq) + SO 4 2- (aq) K a2 = 1.2 x 10 -2

25 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 WHAT ABOUT SULFURIC ACID? For conc. of 1.0 M or higher, only the 1 st step makes an important contribution. For dilute concs. (< 1.0 M),the 2 nd dissociation step makes a contribution. Lets Do # 97 Read Exer & p653

26 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Section 14.8 Acid-Base Properties of Salts Salts = Ionic compounds Salts can behave as ACIDS or BASES.

27 Copyright©2000 by Houghton Mifflin Company. All rights reserved Salts that produce neutral solutions. Composed of cations from strong bases and anions from strong acids. Example: NaCl. NaNO 3, KCl

28 Copyright©2000 by Houghton Mifflin Company. All rights reserved Salts that produce basic solutions. Composed of cations with neutral properties and anions which are the conjugate base of a weak acid. Example: NaCH 3 COO Major species: Na + is neutral CH 3 COO - is conjugate base of weak acid H 2 O is weakly amphoteric

29 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 CH 3 COO 1- + H 2 O CH 3 COOH + OH 1- CH 3 COO 1- in water produces OH 1- ions Basic solution

30 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 CH 3 COO 1- + H 2 O CH 3 COOH + OH 1- K B = [CH 3 COOH] [OH 1- ] [CH 3 COO 1- ] CH 3 COOH + H 2 O CH 3 COO 1- + H 1+ K A = [CH 3 COO 1- ] [ H 1+ ] [CH 3 COOH]

31 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 K A x K B = [CH 3 COO 1- ] [ H 1+ ] x [CH 3 COOH] [OH 1- ] [CH 3 COOH] [CH 3 COO 1- ] = [H 1+ ] [OH 1- ] = K w

32 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31 K a x K b = K w For any weak acid and its conjugate base:

33 Copyright©2000 by Houghton Mifflin Company. All rights reserved Salts that produce acidic solutions. Composed of cations which are the conjugate acid of a weak base and anions with neutral properties. Example: NH 4 Cl Major species: Cl -, H 2 O, & NH 4 + NH 4 1+ (aq) NH 3 (aq) + H 1+ (aq)

34 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 Lets Do Problems # 99, 101, 103, 105a, 107

35 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34 Another type of salt gives acidic solutions those with Hydrated ions of highly charged metal Dissolve AlCl 3 in water. Al(H 2 O) 6 3+ is formed. It is a weak acid. Al(H 2 O) 6 3+ (aq) Al(OH)(H 2 O) 5 2+ (aq) + H + (aq)

36 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35 Figure The Al(H 2 O) 6 3+ Ion

37 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 A high charge on the metal ion (Al 3+ ) polarizes the OH bonds & makes these water molecules more acidic than the OH bonds ordinarily are in water. Lets Do Problem # 109

38 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 Salts with 2 ions that can affect the pH Too complicated to deal with quantitatively. One can predict if Acidic, Basic or Neutral Compare K a & K b 1.If K a > K b, then Acidic 2.If K a < K b, then Basic 3.If K a = K b, then Neutral Lets Do Problem 111

39 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 Acid-Base Properties of Salts See Table 14.6 on page 660

40 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39 Section 14.9 Structure and Acid-Base Properties Two factors for acidity in binary compounds: 4 Bond Polarity (high is good) 4 Bond Strength (low is good) Read pages

41 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 40 Oxyacids HOX Acid Strength Increases with an increase in the number of oxygen atoms.

42 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41 Figure The Effect of the Number of Attached Oxygens on the O-H Bond in a Series of of Chlorine Oxyacids Electronegative oxygen atoms pull electrons away from the Cl atoms & the OH bond. HClO 4 Strongest Acid

43 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42 Hydrated metal ions Example: Al(H 2 O) 6 3+ Greater the charge on a metal ion the greater the acidity of the attached water molecules.

44 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43 Section Acid Base Properties of Oxides A compound containing the HOX group Will produce 1. an acidic soln in water if the OX bond is strong and covalent. Example: H 2 SO 4 ; OS bonds are strong & covalent. Therefore, OH bonds break to produce protons.

45 Copyright©2000 by Houghton Mifflin Company. All rights reserved a basic soln in water if the OX bond is ionic. Example: NaOH ONa bonds are ionic and therefore Break in water to give Na + & OH -

46 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45 Oxides Acidic Oxides (Acid Anhydrides): O X bond is strong and covalent. 4 Dissolve in water & form acidic solns. 4 Non-metal oxides form acid solns in water. SO 2, NO 2, CrO 3 EXAMPLES: SO 3 + H 2 O (l) H 2 SO 4 (aq) SO 2 + H 2 O (l) H 2 SO 3 (aq) CO 2 + H 2 O (l) H 2 CO 3 (aq)

47 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46 Oxides Basic Oxides (Basic Anhydrides): O X bond is ionic. 4 Dissolve in water & form basic solns. 4 Metal oxides form basic solns in water. K 2 O, CaO EXAMPLES CaO (s) + H 2 O (l) Ca(OH) 2 (aq) K 2 O (s) + H 2 O (l) 2 KOH (aq)

48 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47 Section Lewis Acids and Bases Lewis Acid: electron pair acceptor Lewis Base: electron pair donor Acid Base

49 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 48 Figure The Al(H 2 O) 6 3+ Ion

50 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49 Lewis Acid-Base Model – Most general model for acid-base behavior. Lewis Model encompasses the Bronsted- Lowry model, but the reverse is not true. Lewis Acids can be a species without H +.

51 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50 Lets Do Problems # 119, 121, 123, 124. Section Strategy for Solving Acid-Base Problems: A Summary READ!!!!!!!!!!!!!!!!!!! ALSO!! Good Review p


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