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

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

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

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Let’s 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. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Figure 14.10 The Effect of Dilution on the Percent Dissociation and (H+) of a Weak Acid Solution Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Calculating Ka from Percent Dissociation of a Weak Acid See Sample Exercise 14.11 page 643 Let’s Do Problem #65 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 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 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 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. NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq) base acid Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 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. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Bases (continued) weak = very little dissociation (or reaction with water) H3CNH2(aq) + H2O(l)  H3CNH3+(aq) + OH(aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Base Dissociation Constant (Kb) B (aq) + H2O(l)  BH+ (aq) + OH-(aq) Kb = [BH+]_[OH-] [B] These types of Bases are Weak Bases. Kb tend to be small. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 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 Ka1 > Ka2 > Ka3 i.e., each step of dissociation is successively weaker. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 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. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Let’s look at Examples on page 650 H2CO3 · H3PO4 See Table 14.4 on page 651 for Stepwise Dissociation Constants for Common Polyprotic Acids. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

Copyright©2000 by Houghton Mifflin Company. All rights reserved. WHAT ABOUT SULFURIC ACID? Sulfuric acid is unique: (1) It is a strong acid in its 1st dissociation step. H2SO4  H+ (aq) + HSO4- (aq) Ka1 =  It is a weak acid in its second step. HSO4- (aq)  H+ (aq) + SO42- (aq) Ka2 = 1.2 x 10-2 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. WHAT ABOUT SULFURIC ACID? For conc. of 1.0 M or higher, only the 1st step makes an important contribution. For dilute concs. (< 1.0 M) ,the 2nd dissociation step makes a contribution. Let’s Do # 97 Read Exer. 14.16 & 14.17 p653 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

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. NaNO3, KCl Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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: NaCH3COO Major species: Na+ is neutral CH3COO- is conjugate base of weak acid H2O is weakly amphoteric Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. CH3COO1- + H2O  CH3COOH + OH1- CH3COO1- in water produces OH1- ions  Basic solution Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. CH3COO1- + H2O  CH3COOH + OH1- KB = [CH3COOH] [OH1-] [CH3COO1-] CH3COOH + H2O  CH3COO1- + H1+ KA = [CH3COO1-] [ H1+] [CH3COOH] Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. KA x KB = [CH3COO1-] [ H1+] x [CH3COOH] [OH1-] [CH3COOH] [CH3COO1-] = [H1+] [OH1-] = Kw Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. For any weak acid and its conjugate base: Ka x Kb = Kw Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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: NH4Cl Major species: Cl-, H2O, & NH4+ NH41+ (aq)  NH3 (aq) + H1+ (aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Let’s Do Problems # 99, 101, 103, 105a, 107 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Another type of salt gives acidic solutions those with Hydrated ions of highly charged metal Dissolve AlCl3 in water. Al(H2O)63+ is formed. It is a weak acid. Al(H2O)63+ (aq)  Al(OH)(H2O)52+ (aq) + H+ (aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Figure 14.12 The Al(H2O)63+ Ion Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. A high charge on the metal ion (Al3+) polarizes the O—H bonds & makes these water molecules more acidic than the O—H bonds ordinarily are in water. Let’s Do Problem # 109 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Salts with 2 ions that can affect the pH Too complicated to deal with quantitatively. One can predict if Acidic, Basic or Neutral Compare Ka & Kb If Ka > Kb, then Acidic If Ka < Kb, then Basic If Ka = Kb, then Neutral Let’s Do Problem 111 Copyright©2000 by Houghton Mifflin Company. All rights reserved.

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

Section 14.9 Structure and Acid-Base Properties Read pages 661 - 662 Two factors for acidity in binary compounds: Bond Polarity (high is good) Bond Strength (low is good) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Oxyacids H—O—X Acid Strength Increases with an increase in the number of oxygen atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Figure 14.11 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 O—H bond. HClO4 Strongest Acid Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Hydrated metal ions Example: Al(H2O)63+ Greater the charge on a metal ion the greater the acidity of the attached water molecules. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Section 14.10 Acid Base Properties of Oxides A compound containing the H—O—X group Will produce 1. an acidic sol’n in water if the O—X bond is strong and covalent. Example: H2SO4; O—S bonds are strong & covalent. Therefore, O—H bonds break to produce protons. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2. a basic sol’n in water if the O—X bond is ionic. Example: Na—O—H O—Na bonds are ionic and therefore Break in water to give Na+ & OH- Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Oxides Acidic Oxides (Acid Anhydrides): OX bond is strong and covalent. Dissolve in water & form acidic sol’ns. Non-metal oxides form acid sol’ns in water. SO2, NO2, CrO3 EXAMPLES: SO3 + H2O (l)  H2SO4 (aq) SO2 + H2O (l)  H2SO3 (aq) CO2 + H2O (l)  H2CO3 (aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Oxides Basic Oxides (Basic Anhydrides): OX bond is ionic. Dissolve in water & form basic sol’ns. Metal oxides form basic sol’ns in water. K2O, CaO EXAMPLES CaO (s) + H2O (l)  Ca(OH)2 (aq) K2O (s) + H2O (l)  2 KOH (aq) Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Section 14.11 Lewis Acids and Bases Lewis Acid: electron pair acceptor Lewis Base: electron pair donor Acid Base Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Figure 14.12 The Al(H2O)63+ Ion Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 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+. Copyright©2000 by Houghton Mifflin Company. All rights reserved.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. Let’s Do Problems # 119, 121, 123, 124. Section 14.12 Strategy for Solving Acid-Base Problems: A Summary READ!!!!!!!!!!!!!!!!!!! ALSO!! Good “Review” p. 668-672 Copyright©2000 by Houghton Mifflin Company. All rights reserved.